Method and device for relay UE to add source UE for inter-UE relay communication

Abstract

The invention discloses a method and equipment for relay UE to add source UE for relay communication between UEs. In one embodiment, a target-end user equipment establishes a PC5 connection with a relay user equipment to support inter-user equipment relay communication between a first source-end user equipment and the target-end user equipment via the relay user equipment. The target user equipment also receives a request message from the relay user equipment requesting establishment of another PC5 connection with the relay user equipment to support inter-user equipment relay communication with the second source user equipment via the relay user equipment. Further, in response to receiving the request message, the target-end user equipment sends a rejection message to the relay user equipment if the PC5 connection exists.

Description

Technical Field

[0001] The present disclosure relates generally to wireless communication networks, and more particularly to a method and apparatus for adding a source UE to a relay user equipment (UE) for inter-UE relay communication in a wireless communication system. Background Art

[0002] With the rapidly growing demand for transferring large amounts of data to and from mobile communication devices, traditional mobile voice communication networks have evolved into networks that use Internet Protocol (IP) packet communications. This IP packet communication can provide IP-based voice, multimedia, multicast, and on-demand communication services to users of mobile communication devices.

[0003] An exemplary network architecture is the Evolved Universal Terrestrial Radio Access Network (E-UTRAN). The E-UTRAN system can provide high data throughput to enable the aforementioned IP-based voice and multimedia services. Currently, the 3GPP standards organization is discussing new next-generation (e.g., 5G) radio technologies. Consequently, changes to the current body of 3GPP standards are currently being submitted and considered to evolve and complete the 3GPP standards. Summary of the Invention

[0004] Disclosed are a method and apparatus for a target UE. In one embodiment, the target UE establishes a PC5 connection with a relay UE to support inter-UE relay communication between a first source UE and the target UE via the relay UE. The target UE also receives a request message from the relay UE requesting to establish another PC5 connection with the relay UE to support inter-UE relay communication with a second source UE via the relay UE. Furthermore, in response to receiving the request message, if a PC5 connection exists, the target UE sends a rejection message to the relay UE. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1 The drawing shows a wireless communication system according to an exemplary embodiment.

[0006] Figure 2 is a block diagram of a transmitter system (also referred to as an access network) and a receiver system (also referred to as a user equipment or UE) according to an exemplary embodiment.

[0007] Figure 3 is a functional block diagram of a communication system according to an exemplary embodiment.

[0008] Figure 4 According to an exemplary embodiment Figure 3 Functional block diagram of the program code.

[0009] Figure 5 It is 3GPP TS23.304V18.2.0 Figure 4 .Reproduction of 2.8-1.

[0010] Figure 6 It is 3GPP TS23.304V18.2.0 Figure 6 .Reproduction of 3.2.4.2-1.

[0011] Figure 7 It is 3GPP TS23.304V18.2.0 Figure 6 .Reproduction of 3.2.4.3-1.

[0012] Figure 8 It is 3GPP TS23.304V18.2.0 Figure 6 .Reproduction of 4.3.1-1.

[0013] Figure 9 It is 3GPP TS23.304V18.2.0 Figure 6 .Reproduction of 4.3.2-1.

[0014] Figure 10 It is 3GPP TS23.304V18.2.0 Figure 6 .Reproduction of 4.3.4-1.

[0015] Figure 11 It is 3GPP TS23.304V18.2.0 Figure 6 .7.1.1-1 reappearance.

[0016] Figure 12 It is 3GPP TS23.304V18.2.0 Figure 6 .7.1.4-1 reappearance.

[0017] Figure 13 It is 3GPP TS23.304V18.2.0 Figure 6 .7.2-1 reappearance.

[0018] Figure 14 It is 3GPP TS23.304V18.2.0 Figure 6 .7.3.2-1 reappearance.

[0019] Figure 15 It is 3GPP TS23.304V18.2.0 Figure 6 .7.3.3-1 reappearance.

[0020] Figure 16 It is 3GPP TS24.554V18.1.0 Figure 7 .2.2.2.1 reappearance.

[0021] Figure 17 It is 3GPP TS24.554V18.1.0 Figure 7 .2.2.2.2 reappearance.

[0022] Figure 18 It is 3GPP TS24.554V18.1.0 Figure 7 .Reproduction of 2.3.2.1.

[0023] Figure 19 It is 3GPP TS24.554V18.1.0 Figure 7 .Reproduction of 2.3.2.2.

[0024] Figure 20 It is 3GPP TS24.554V18.1.0 Figure 7 .Reproduction of 2.10.2.1.

[0025] Figure 21 is a flow chart according to an exemplary embodiment.

[0026] Figure 22 is a flow chart according to an exemplary embodiment.

[0027] Figure 23 is a flow chart according to an exemplary embodiment.

[0028] Figure 24 is a flow chart according to an exemplary embodiment.

[0029] Figure 25 is a flow chart according to an exemplary embodiment. DETAILED DESCRIPTION

[0030] The exemplary wireless communication systems and devices described below employ wireless communication systems that support broadcast services. Wireless communication systems are widely deployed to provide various types of communications, such as voice, data, etc. These systems can be based on code division multiple access (CDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), 3GPP Long Term Evolution (LTE) radio access, 3GPP LTE-A or LTE Advanced (Long Term Evolution Advanced), 3GPP2 Ultra Mobile Broadband (UMB), WiMax, 3GPP New Radio (NR), or some other modulation technology.

[0031] Specifically, the exemplary wireless communication system apparatus described below may be designed to support one or more standards, such as those provided by an association named “3rd Generation Partnership Project” (referred to herein as 3GPP), including: TS 23.304 V18.2.0, “Proximity-based Services (ProSe) in 5G System (5GS) (Release 18)”; and TS 24.554 V18.1.0, “Proximity Services (ProSe) Protocol Aspects in 5G System (5GS); Stage 3 (Release 18)”. The standards and documents listed above are expressly incorporated herein by reference in their entirety.

[0032] Figure 1 1. A multiple access wireless communication system according to an embodiment of the present invention is shown. An access network 100 (AN) includes multiple antenna groups, one of which includes antennas 104 and 106, another includes antennas 108 and 110, and another includes antennas 112 and 114. Figure 1, only two antennas are shown for each antenna group, but each antenna group may utilize more or fewer antennas. Access terminal 116 (AT) communicates with antennas 112 and 114, where antennas 112 and 114 transmit information to access terminal 116 via forward link 120 and receive information from access terminal 116 via reverse link 118. Access terminal 122 communicates with antennas 106 and 108, where antennas 106 and 108 transmit information to access terminal 122 via forward link 126 and receive information from access terminal 122 via reverse link 124. In an FDD system, communication links 118, 120, 124, and 126 may use different frequencies for communication. For example, forward link 120 may use a different frequency than that used by reverse link 118.

[0033] Each antenna group and / or the area in which they are designed to communicate is often referred to as a sector of the access network. In an embodiment, the antenna groups are each designed to communicate with access terminals in a sector of the area covered by the access network 100.

[0034] In communicating via forward links 120 and 126, the transmit antennas of access network 100 may utilize beamforming to improve the signal-to-noise ratio of the forward links for the different access terminals 116 and 122. Furthermore, an access network that uses beamforming to transmit to access terminals randomly dispersed throughout the coverage area of ​​the access network may cause less interference to access terminals in neighboring cells than an access network that transmits to all of its access terminals via a single antenna.

[0035] An access network (AN) may be a fixed station or base station for communicating with a terminal and may also be referred to as an access point, Node B, base station, enhanced base station, evolved Node B (eNodeB), network node, network, or some other terminology. An access terminal (AT) may also be referred to as user equipment (UE), a wireless communication device, terminal, access terminal, or some other terminology.

[0036] Figure 2 is a simplified block diagram of an embodiment of a transmitter system 210 (also referred to as an access network) and a receiver system 250 (also referred to as an access terminal (AT) or user equipment (UE)) in a MIMO system 200. At the transmitter system 210, traffic data for several data streams is provided from a data source 212 to a transmit (TX) data processor 214.

[0037] In one embodiment, each data stream is transmitted through a respective transmit antenna. TX data processor 214 formats, codes, and interleaves the traffic data for each data stream based on a particular coding scheme selected for that data stream to provide coded data.

[0038] The coded data for each data stream may be multiplexed with pilot data using OFDM techniques. The pilot data is typically a known data pattern that is processed in a known manner and may be used at the receiver system to estimate the channel response. The multiplexed pilot and coded data for each data stream is then modulated (i.e., symbol mapped) based on a particular modulation scheme selected for that data stream (e.g., BPSK, QPSK, M-PSK, or M-QAM) to provide modulation symbols. The data rate, coding, and modulation for each data stream may be determined by instructions executed by processor 230.

[0039] The modulation symbols for all data streams are then provided to a TX MIMO processor 220, which may further process the modulation symbols (e.g., for OFDM). The TX MIMO processor 220 then converts the N T The modulation symbol stream is provided to N T transmitters (TMTR) 222a through 222t. In certain embodiments, TX MIMO processor 220 applies beamforming weights to the symbols of the data streams and to the antenna from which the symbol is being transmitted.

[0040] Each transmitter 222 receives and processes a respective symbol stream to provide one or more analog signals, and further conditions (eg, amplifies, filters, and upconverts) the analog signals to provide a modulated signal suitable for transmission via the MIMO channel. T The antennas 224a to 224t transmit N signals from transmitters 222a to 222t. T a modulated signal.

[0041] At the receiver system 250, N R The transmitted modulated signals are received by each antenna 252a through 252r and the received signal from each antenna 252 is provided to a respective receiver (RCVR) 254a through 254r. Each receiver 254 conditions (e.g., filters, amplifies, and downconverts) a respective received signal, digitizes the conditioned signal to provide samples, and further processes the samples to provide a corresponding "received" symbol stream.

[0042] RX data processor 260 then extracts the N R The receiver 254 receives and processes N R receive symbol streams to provide N TThe RX data processor 260 then demodulates, deinterleaves, and decodes each detected symbol stream to recover the traffic data for the data stream. The processing by the RX processor 260 is complementary to that performed by the TX MIMO processor 220 and the TX data processor 214 at the transmitter system 210.

[0043] Processor 270 periodically determines which pre-coding matrix to use (discussed below). Processor 270 formulates a reverse link message comprising a matrix index portion and a rank value portion.

[0044] The reverse link message may include various types of information related to the communication link and / or the received data stream. The reverse link message is then processed by the TX data processor 238 (which also receives traffic data for a number of data streams from the data source 236), modulated by the modulator 280, conditioned by the transmitters 254a through 254r, and transmitted back to the transmitter system 210.

[0045] At transmitter system 210, the modulated signal from receiver system 250 is received by antenna 224, conditioned by receiver 222, demodulated by demodulator 240, and processed by RX data processor 242 to extract the reverse link message transmitted by receiver system 250. Processor 230 then determines which precoding matrix to use to determine the beamforming weights and then processes the extracted message.

[0046] Steering Figure 3 , this figure shows an alternative simplified functional block diagram of a communication device according to one embodiment of the present invention. Figure 3 As shown in FIG, the communication device 300 in the wireless communication system can be used to implement Figure 1 UE (or AT) 116 and 122 in or Figure 1 The base station (or AN) 100 in the wireless communication system is preferably an NR system. The communication device 300 may include an input device 302, an output device 304, a control circuit 306, a central processing unit (CPU) 308, a memory 310, a program code 312, and a transceiver 314. The control circuit 306 executes the program code 312 in the memory 310 through the CPU 308, thereby controlling the operation of the communication device 300. The communication device 300 can receive signals input by the user through the input device 302 (for example, a keyboard or a keypad), and can output images and sounds through the output device 304 (for example, a display or a speaker). The transceiver 314 is used to receive and transmit wireless signals to pass the received signal to the control circuit 306 and wirelessly output the signal generated by the control circuit 306. The communication device 300 in the wireless communication system can also be used to implement Figure 1 AN 100 in.

[0047] Figure 4 According to one embodiment of the present invention Figure 3 . In this embodiment, program code 312 includes an application layer 400, a layer 3 portion 402, and a layer 2 portion 404, and is coupled to a layer 1 portion 406. Layer 3 portion 402 generally performs radio resource control. Layer 2 portion 404 generally performs link control. Layer 1 portion 406 generally performs physical connectivity.

[0048] 3GPP TS23.304 introduces the following:

[0049] 4.2.8 5G ProSe Inter-UE Relay Reference Architecture

[0050] Figure 4 .2.8-1 shows the Layer 2 and Layer 3 5G ProSe inter-UE relay reference architecture. 5G ProSe UEs communicate with each other via the 5G ProSe inter-UE relay.

[0051] [3GPP TS 23.304 V18.2.0 titled "Reference architecture for 5G ProSe inter-UE relay" Figure 4 .2.8-1 reproduced as Figure 5 ]

[0052] Each 5G ProSe end UE and 5G ProSe inter-UE relay may have a subscription from the same PLMN or different PLMNs.

[0053] […]

[0054] 5.8.4 Identifiers for 5G ProSe Inter-UE Relay Discovery

[0055] 5.8.4.1 Overview

[0056] The 5G ProSe inter-UE relay discovery message contains two groups of identifiers, namely the direct discovery group and the inter-UE relay discovery group.

[0057] - The Direct Discovery Identifier Group is part of the content of the 5G ProSe Direct Discovery message, as defined in section 5.8.1.

[0058] - The Inter-UE Relay Discovery Identifier Group contains information to support the discovery of 5G ProSe Inter-UE Relay and extended direct discovery. The 5G ProSe Inter-UE Relay shall modify the Inter-UE Relay Discovery Identifier Group and forward the direct discovery group and the Inter-UE Relay Discovery Identifier Group during the discovery procedure.

[0059] 5.8.4.2 Common Identifiers for 5G ProSe Inter-UE Relay Discovery

[0060] The following parameters are used for the 5G ProSe Inter-UE Relay Discovery Notification message (Model A), where the source layer 2 ID and destination layer 2 ID are used to send and receive the message, and the user information ID and relay service code are included in the message:

[0061] - Source Layer 2 ID: The 5G ProSe Inter-UE Relay selects the source Layer 2 ID for the 5G ProSe Inter-UE Relay Discovery Notification message.

[0062] - Destination Layer 2 ID: The destination Layer 2 ID for the 5G ProSe Inter-UE Relay Discovery Notification message is selected based on the configuration described in Section 5.1.5.1.

[0063] -User Information ID of 5G ProSe Inter-UE Relay: Provides information about 5G ProSe Inter-UE Relay.

[0064] -5G ProSe UE user information ID list: provides information about 5G ProSe UE.

[0065] -Relay Service Code: Information used to indicate the connectivity service provided by the 5G ProSe inter-UE relay for the 5G ProSe end UE.

[0066] The following parameters are used for the 5G ProSe Inter-UE Relay Discovery Solicitation message (Model B) between the discoverer 5G ProSe end UE and the 5G ProSe Inter-UE Relay, where the source Layer 2 ID and the destination Layer 2 ID are used to send and receive the message, and the user information ID and relay service code are included in the message:

[0067] - Source Layer 2 ID: The discoverer 5G ProSe UE selects the source Layer 2 ID for relaying the discovery request message between 5G ProSe UEs.

[0068] - Destination Layer 2 ID: The destination Layer 2 ID for the 5G ProSe Inter-UE Relay Discovery Solicitation message is selected based on the configuration described in Section 5.1.5.1.

[0069] -User information ID of the discoverer 5G ProSe UE: provides information about the discoverer 5G ProSe UE.

[0070] -User information ID of the discovered 5G ProSe UE: provides information about the discovered 5G ProSe UE.

[0071] -Relay Service Code: Information about the connectivity services that the discoverer 5G ProSe-side UE is interested in.

[0072] The following parameters are used for the 5G ProSe Inter-UE Relay Discovery Response message (Model B) between the discoverer 5G ProSe-side UE and the 5G ProSe Inter-UE Relay, where the source Layer 2 ID and the destination Layer 2 ID are used to send and receive messages, and the user information ID and relay service code are included in the message:

[0073] - Source Layer 2 ID: The 5G ProSe Inter-UE Relay selects the source Layer 2 ID for the 5G ProSe Inter-UE Relay Discovery Response message.

[0074] - Destination Layer 2 ID: set to the source Layer 2 ID of the received 5G ProSe Inter-UE Relay Discovery Request message.

[0075] -User information ID of the discovered 5G ProSe UE: provides information about the discovered 5G ProSe UE.

[0076] -User Information ID of 5G ProSe Inter-UE Relay: Provides information about 5G ProSe Inter-UE Relay.

[0077] -Relay Service Code: Identifies the connectivity service provided by the 5G ProSe inter-UE relay to the 5G ProSe end UE, matching the relay service code from the corresponding discovery request message.

[0078] The following parameters are used for the 5G ProSe Inter-UE Relay Discovery Solicitation message (Model B) between the 5G ProSe Inter-UE Relay and the discoverer 5G ProSe end UE, where the source layer 2 ID and the destination layer 2 ID are used to send and receive the message, and the user information ID and relay service code are included in the message:

[0079] - Source Layer 2 ID: The 5G ProSe Inter-UE Relay selects the source Layer 2 ID for the 5G ProSe Inter-UE Relay Discovery Request message.

[0080] - Destination Layer 2 ID: The destination Layer 2 ID for the 5G ProSe Inter-UE Relay Discovery Solicitation message is selected based on the configuration described in Section 5.1.5.1.

[0081] -User information ID of the discoverer 5G ProSe UE: provides information about the discoverer 5G ProSe UE.

[0082] -User information ID of the discovered 5G ProSe UE: provides information about the discovered 5G ProSe UE.

[0083] -User Information ID of 5G ProSe Inter-UE Relay: Provides information about 5G ProSe Inter-UE Relay.

[0084] -Relay Service Code: Identifies the connectivity service provided by the 5G ProSe inter-UE relay to the 5G ProSe end UE.

[0085] The following parameters are used for the 5G ProSe Inter-UE Relay Discovery Response message (Model B) between the 5G ProSe Inter-UE Relay and the discoverer 5G ProSe end UE, where the source layer 2 ID and the destination layer 2 ID are used to send and receive the message, and the user information ID and relay service code are included in the message:

[0086] - Source Layer 2 ID: The discoverer 5G ProSe UE selects the source Layer 2 ID for relaying the discovery response message between 5G ProSe UEs.

[0087] - Destination Layer 2 ID: set to the source Layer 2 ID of the received 5G ProSe Inter-UE Relay Discovery Request message.

[0088] -User information ID of the discovered 5G ProSe UE: provides information about the discovered 5G ProSe UE.

[0089] -User information ID of the discoverer 5G ProSe UE: provides information about the discoverer 5G ProSe UE.

[0090] -Relay Service Code: Identifies the connectivity service provided by the 5G ProSe inter-UE relay to the 5G ProSe end UE, matching the relay service code from the corresponding discovery request message.

[0091] NOTE: UE implementations need to ensure that when the UE self-selects a source Layer-2 ID, the self-selected source Layer-2 ID is different between 5G ProSe direct discovery (including 5G ProSe UE to network relay discovery and 5G ProSe inter-UE relay discovery) in section 6.3.2 and 5G ProSe direct communication (including 5G ProSe UE to network relay communication and 5G ProSe inter-UE relay communication) in sections 6.4, 6.5 and 6.7, and is different from any other provisioned destination Layer-2 ID described in section 5.1 and any other self-selected source Layer-2 ID used for simultaneous 5G ProSe direct discovery (including 5G ProSe UE to network relay discovery and 5G ProSe inter-UE relay discovery) with different discovery models.

[0092] 5.8.5 Identifier for 5G ProSe Inter-UE Relay Communication with Integrated Discovery

[0093] For the broadcast direct communication request message on the first-hop PC5 reference point, the source Layer 2 ID is selected by the source 5G ProSe end UE itself, and the destination Layer 2 ID is selected based on the configuration described in Section 5.1.

[0094] For the Broadcast Direct Communication Request message over the second-hop PC5 reference point, the source Layer 2 ID is selected by the 5G ProSe Inter-UE Relay itself, and the destination Layer 2 ID is selected based on the configuration described in Section 5.1.

[0095] The 5G ProSe inter-UE relay may send a unicast direct communication request message to the target 5G ProSe end UE by setting the destination layer 2 ID with the received unicast destination layer 2 ID of the target 5G ProSe end UE specified in Section 6.4.3.7. The source layer 2 ID is selected by the 5G ProSe inter-UE relay itself.

[0096] For unicast direct communication acceptance messages, the source layer 2 ID is selected by the target 5G ProSe UE or the 5G ProSe inter-UE relay.

[0097] […]

[0098] 6.3.2.4 5G ProSe Inter-UE Relay Discovery

[0099] 6.3.2.4.1 Overview

[0100] 5G ProSe inter-UE relay discovery is suitable for both 5G ProSe layer 3 and layer 2 inter-UE relay discovery for public safety purposes and commercial services. To perform 5G ProSe inter-UE relay discovery, the 5G ProSe-side UE and the 5G ProSe inter-UE relay are pre-configured or provisioned with the relevant information described in Section 5.1.

[0101] The Relay Service Code (RSC) is used for 5G ProSe inter-UE relay discovery to indicate the connectivity service provided by the 5G ProSe inter-UE relay to the 5G ProSe end UE. The RSC is pre-configured or provisioned on the 5G ProSe inter-UE relay and the 5G ProSe end UE, as defined in Section 5.1. The 5G ProSe inter-UE relay and the 5G ProSe end UE are aware of whether the RSC is providing 5G ProSe Layer 2 or Layer 3 inter-UE relay service based on the policy specified in Section 5.1. A 5G ProSe inter-UE relay that supports multiple RSCs advertises the RSCs using multiple discovery messages, with one RSC per discovery message.

[0102] 6.3.2.4.2 Procedure for 5G ProSe Inter-UE Relay Discovery with Model A

[0103] Figure 6 The procedure for 5G ProSe inter-UE discovery with Model A is described in .3.2.4.2-1.

[0104] [3GPP TS 23.304 V18.2.0 titled "5G ProSe Inter-UE Relay Discovery with Model A" Figure 6 .3.2.4.2-1 Reproduced as Figure 6 ]

[0105] 1. The 5G ProSe Inter-UE Relay has discovered other UEs in the vicinity (eg, via a previous 5G ProSe Inter-UE Relay discovery or 5G ProSe Inter-UE Relay communication procedure). The 5G ProSe Inter-UE Relay obtains the user information IDs of other UEs in the vicinity for each RSC.

[0106] 2.5G ProSe Inter-UE Relay sends an Inter-UE Relay Discovery Notification message. The Inter-UE Relay Discovery Notification message contains the discovery message type, the user information ID of the 5G ProSe Inter-UE Relay, the RSC, and a list of user information IDs of the 5G ProSe UEs. It is sent using the source layer 2 ID and the destination layer 2 ID, as described in Section 5.8.4.

[0107] 5G ProSe inter-UE relay will only notify the user information IDs of other UEs in the vicinity that provided relay_indication when previously discovered.

[0108] The 5G ProSe UE monitors the notification message from the 5G ProSe inter-UE relay. The 5G ProSe UE determines the destination Layer 2 ID for signaling reception as specified in Section 5.1.

[0109] 6.3.2.4.3 Procedure for 5G ProSe Inter-UE Relay Discovery with Model B

[0110] Figure 6 The procedure for 5G ProSe inter-UE relay discovery with Model B is described in .3.2.4.3-1.

[0111] [3GPP TS 23.304 V18.2.0 titled "5G ProSe Inter-UE Relay Discovery with Model B" Figure 6 .3.2.4.3-1 Reproduced as Figure 7 ]

[0112] 1. The discoverer 5G ProSe UE (UE-1) sends a 5G ProSe Inter-UE Relay Discovery Request message. The 5G ProSe Inter-UE Relay Discovery Request message contains the discovery message type, its own user information ID, RSC, and the user information ID of the discoverer 5G ProSe UE (UE-2), and is sent using the source layer 2 ID and the destination layer 2 ID, as described in Section 5.8.4.

[0113] The 5G ProSe inter-UE relay determines the destination Layer 2 ID for signaling reception as specified in section 5.1.

[0114] 2. The 5G ProSe Inter-UE Relay matching the RSC sends a 5G ProSe Inter-UE Relay Discovery Solicitation message. The 5G ProSe Inter-UE Relay Discovery Solicitation message contains the discovery message type, the user information ID of the discoverer 5G ProSe UE (UE-1), the user information ID of the Inter-UE Relay, the RSC, and the user information ID of the discoverer 5G ProSe UE (UE-2), and is sent using the source Layer 2 ID and the destination Layer 2 ID, as described in Section 5.8.4.

[0115] The 5G ProSe-side UE determines the destination Layer 2 ID for signaling reception as specified in Section 5.1.

[0116] 3. The discoverer 5G ProSe side UE (UE-2) that matches the value of RSC and the user information ID of the discoverer 5G ProSe side UE (UE-2) responds to the 5G ProSe inter-UE relay with a 5G ProSe inter-UE relay discovery response message. The 5G ProSe inter-UE relay discovery response message contains the type of discovery message, RSC, the user information ID of the discoverer 5G ProSe side UE (UE-1) and its own user information ID, and is sent using the source layer 2 ID and the destination layer 2 ID, as described in Section 5.8.4. If the discoverer 5G ProSe side UE (UE-2) receives multiple inter-UE relay discovery solicitation messages from different 5G ProSe inter-UE relays, it can choose whether to respond to the 5G ProSe inter-UE relay (e.g., based on the PC5 signal strength of each message received).

[0117] 4.5G ProSe Inter-UE Relay sends a 5G ProSe Inter-UE Relay Discovery Response message. The 5G ProSe Inter-UE Relay Discovery Response message contains the discovery message type, the user information ID of the inter-UE relay, the RSC, and the user information ID of the discovered 5G ProSe end UE (UE-2), and is sent using the source layer 2 ID and the destination layer 2 ID, as described in Section 5.8.4.

[0118] 6.3.2.4.4 Candidate 5G ProSe Inter-UE Relay Discovery

[0119] This procedure for candidate 5G ProSe inter-UE relay discovery supports negotiated relay reselection when the discoverer-side UE discovers a candidate 5G ProSe inter-UE relay, as described in Section 6.7.4.

[0120] The procedure for 5G ProSe inter-UE relay discovery with Model B is used (see section 6.3.2.4.3), with the following differences:

[0121] -Step 1: In the 5G ProSe Inter-UE Relay Discovery Solicitation message, no RSC is included, and the User Information ID of the discoverer 5G ProSe UE is replaced with the User Information ID of the candidate 5G ProSe Inter-UE Relay. If the 5G ProSe UE receives the Layer 2 ID of the candidate 5G ProSe Inter-UE Relay in the Link Modification Request message, it may set the Layer 2 ID of the candidate 5G ProSe Inter-UE Relay as the destination Layer 2 ID.

[0122] - Steps 2 and 3 are skipped because RSC does not exist in the received 5G ProSe Inter-UE Relay Discovery Request message.

[0123] - Step 4: If the 5G ProSe Inter-UE Relay matches the User Information ID of the candidate 5G ProSe Inter-UE Relay received in the 5G ProSe Inter-UE Relay Discovery Request, it sends a 5G ProSe Inter-UE Relay Discovery Response without including the User Information ID of the discovered 5G ProSe UE.

[0124] […]

[0125] 6.4.3 5G ProSe Direct Communication in Unicast Mode

[0126] 6.4.3.1 Layer 2 link establishment over PC5 reference point

[0127] To perform unicast mode ProSe direct communication over the PC5 reference point, the UE is configured with relevant information as described in Section 5.1.3.

[0128] Figure 6 .4.3.1-1 shows the Layer 2 link establishment procedure for unicast mode ProSe direct communication over the PC5 reference point.

[0129] [3GPP TS 23.304 V18.2.0 entitled "Layer 2 Link Establishment Procedure" Figure 6 .4.3.1-1 Reproduced as Figure 8 ]

[0130] 1. The UE determines the destination Layer 2 ID for signaling reception for PC5 unicast link establishment as specified in section 5.8.2.4.

[0131] 2. The ProSe application layer in UE-1 provides application information for PC5 unicast communication. The application information includes ProSe service information and the UE's application layer ID. The target UE's application layer ID may be included in the application information.

[0132] The ProSe application layer in UE-1 may provide the ProSe application requirements for this unicast communication. UE-1 determines the PC5 QoS parameters and PFI as specified in Section 5.6.1.

[0133] If UE-1 decides to reuse the existing PC5 unicast link as specified in section 5.3.4, the UE triggers the Layer 2 Link Modification procedure as specified in section 6.4.3.4.

[0134] 3. UE1 sends a direct communication request message to initiate the unicast layer 2 link establishment procedure. The direct communication request message contains:

[0135] - Source user information: the application layer ID of the originating UE (ie, the application layer ID of UE-1).

[0136] If the ProSe application layer provides the target UE's application layer ID in step 2, the following information is included:

[0137] - Target user information: the application layer ID of the target UE (ie, the application layer ID of UE-2).

[0138] -ProSe service information: information about the ProSe identifier requesting Layer 2 link establishment.

[0139] - Security information: information used to establish security.

[0140] NOTE 1: Security information and the required protection of source user information and destination user information are defined in TS 33.503

[29] .

[0141] The source layer 2 ID and destination layer 2 ID used to send the direct communication request message are determined as specified in sections 5.8.2.1 and 5.8.2.4. The destination layer 2 ID can be a broadcast or unicast layer 2 ID. When using a unicast layer 2 ID, the target user information will be included in the direct communication request message.

[0142] UE- 1 transmits a direct communication request message via PC 5 by broadcast or unicast using the source layer 2 ID and the destination layer 2 ID.

[0143] The default PC5 DRX configuration may be used to transmit and receive this message (see TS 38.300

[12] ).

[0144] 4. Establish security for UE-1 as follows:

[0145] 4a. If the target user information is included in the direct communication request message, the target UE, ie, UE-2, responds by establishing security with UE-1.

[0146] 4b. If the target user information is not included in the direct communication request message, the UE interested in using the announced ProSe service over the PC5 unicast link with UE-1 responds by establishing security with UE-1.

[0147] NOTE 2: Signalling for security procedures is defined in TS 33.503

[29] .

[0148] When security protection is enabled, UE-1 sends the following information to the target UE:

[0149] - If using IP communication:

[0150] -IP Address Configuration: For IP communication, this link requires IP address configuration, and it indicates one of the following values:

[0151] - "DHCPv4 server", provided that only IPv4 address allocation mechanisms are supported by the initiating UE, i.e. it acts as a DHCPv4 server; or

[0152] - "IPv6 router", provided that only IPv6 address allocation mechanisms are supported by the originating UE, i.e. it acts as an IPv6 router; or

[0153] - "DHCPv4 server and IPv6 router", provided that both IPv4 and IPv6 address allocation mechanisms are supported by the initiating UE; or

[0154] - "Address allocation not supported", if both IPv4 and IPv6 address allocation mechanisms are not supported by the originating UE.

[0155] - Link-local IPv6 address: If UE-1 does not support the IPv6 IP address allocation mechanism, i.e. the IP address configuration indicates "address allocation not supported", then a link-local IPv6 address is formed locally based on RFC 4862

[17] .

[0156] - QoS information: Information about PC5 QoS flows. For each PC5 QoS flow, PFI and corresponding PC5 QoS parameters (ie, PQI and conditionally other parameters such as MFBR / GFBR, etc.) and optionally an associated ProSe identifier.

[0157] -Optional PC5 QoS rules.

[0158] The source layer 2 ID used for the security establishment procedure is determined as specified in sections 5.8.2.1 and 5.8.2.4. The destination layer 2 ID is set to the source layer 2 ID of the received direct communication request message.

[0159] After receiving the Security Setup Procedure message, UE-1 obtains the Layer 2 ID of the peer UE for future communications for signaling and data traffic for this unicast link.

[0160] 5. The target UE, which has successfully established security with UE-1, sends a direct communication acceptance message to UE-1:

[0161] 5a. (Layer 2 Link Establishment towards UE) If the direct communication request message contains target user information, then if the application layer ID for UE-2 matches, the target UE, i.e. UE-2, responds with a direct communication accept message.

[0162] 5b. (Layer 2 Link Establishment for ProSe Services) If the Direct Communication Request message does not contain target user information, the UE interested in using the notified ProSe service (in Figure 6 .UE-2 and UE-4 in 4.3.1-1) respond to the request by sending a direct communication accept message.

[0163] The direct communication acceptance message includes:

[0164] -Source user information: the application layer ID of the UE that sends the direct communication accept message.

[0165] - QoS information: Information about PC5 QoS flows. For each PC5 QoS flow, PFI and corresponding PC5 QoS parameters requested by UE-1 (ie, PQI and conditionally other parameters such as MFBR / GFBR, etc.) and optionally an associated ProSe identifier.

[0166] -Optional PC5 QoS rules.

[0167] - If using IP communication:

[0168] -IP Address Configuration: For IP communication, this link requires IP address configuration, and it indicates one of the following values:

[0169] - "DHCPv4 server", provided that only IPv4 address allocation mechanisms are supported by the target UE, i.e. acting as a DHCPv4 server; or

[0170] - "IPv6 Router", provided that only IPv6 address allocation mechanisms are supported by the target UE, i.e. it acts as an IPv6 router; or

[0171] - "DHCPv4 server and IPv6 router", provided that both IPv4 and IPv6 address allocation mechanisms are supported by the target UE; or

[0172] - "Address allocation not supported", if both IPv4 and IPv6 address allocation mechanisms are not supported by the target UE.

[0173] - Link-local IPv6 address: If the target UE does not support the IPv6 IP address allocation mechanism, i.e., the IP address configuration indicates "address allocation not supported" and UE-1 includes a link-local IPv6 address in the Direct Communication Request message, a link-local IPv6 address is formed locally based on RFC4862

[17] . The target UE shall include a non-conflicting link-local IPv6 address.

[0174] If two UEs (ie, the initiating UE and the target UE) are selected to use link-local IPv6 addresses, then the two UEs shall disable dual address detection as defined in RFC 4862

[17] .

[0175] NOTE 3: When the initiating UE or target UE indicates support for IPv6 routers, the corresponding address configuration procedure shall be implemented after the Layer 2 link is established and the link-local IPv6 address shall be ignored.

[0176] The ProSe layer of the UE that has established a PC5 unicast link passes the PC5 link identifier and PC5 unicast link-related information assigned to the unicast link down to the AS layer. The PC5 unicast link-related information includes Layer 2 ID information (i.e., source Layer 2 ID and destination Layer 2 ID). This enables the AS layer to maintain the PC5 link identifier and PC5 unicast link-related information.

[0177] Two UEs may negotiate the PC5 DRX configuration in the AS layer, and PC5 DRX parameter values ​​may be configured for each pair of source / destination Layer 2 IDs in the AS layer.

[0178] 6. ProSe data is transmitted via the established unicast link as follows:

[0179] The PC5 link identifier and PFI are provided to the AS layer together with the ProSe data.

[0180] Additionally, layer 2 ID information (ie, source layer 2 ID and destination layer 2 ID) is optionally provided to the AS layer.

[0181] NOTE 4: Providing the Layer 2 ID information to the AS layer is UE implementation dependent.

[0182] UE-1 sends ProSe data using a source Layer 2 ID (ie, the Layer 2 ID of UE-1 for this unicast link) and a destination Layer 2 ID (ie, the Layer 2 ID of the peer UE for this unicast link).

[0183] NOTE 5: The PC5 unicast link is bidirectional, so UE-1's peer UE can send ProSe data to UE-1 through the unicast link with UE-1.

[0184] […]

[0185] 6.4.3.2 Link Identifier Update for Unicast Links

[0186] Figure 64.3.2-1 shows the link identifier update procedure for unicast links. When privacy requirements are configured for ProSe identifiers associated with unicast links, the identifiers (e.g., application layer ID, source layer 2 ID, and IP address / prefix) used for unicast mode of 5G ProSe communication over the PC5 reference point will change over time, as specified in sections 5.8.2.1 and 5.8.2.4. The UE may decide to change the identifier for other reasons, such as application layer requirements. This procedure is used to update and exchange new identifiers between the source UE and the peer UE for the unicast link before using the new identifier to prevent service interruption. This procedure is performed on security-protected unicast links when there are privacy requirements as indicated above.

[0187] If a UE has multiple unicast links using the same application layer ID or layer 2 ID, the UE needs to perform a link identifier update procedure over each of the unicast links.

[0188] [3GPP TS 23.304 V18.2.0 entitled "Link Identifier Update Procedure" Figure 6 .4.3.2-1 Reproduced as Figure 9 ]

[0189] 0. UE-1 and UE-2 have a unicast link established as described in Section 6.4.3.1.

[0190] 1. UE-1 decides to change its identifier, for example due to a change in the application layer ID or a timer expiration. UE-1 generates its new layer 2 ID and sends a Link Identifier Update Request message to UE-2 using the old identifier.

[0191] The Link Identifier Update Request message contains the new identifier to be used (including the new Layer 2 ID, security information, an optional new application layer ID, and an optional new IP address / prefix (if IP communication is used)). If security is configured for the unicast link, the new identifier is encrypted to protect privacy. After sending the Link Identifier Update Request message, if UE-1 has data to send, UE-1 continues to send data traffic to UE-2 using the old identifier until UE-1 sends a Link Identifier Update Confirm message to UE-2.

[0192] NOTE 1: The timer runs for each source layer 2 ID.

[0193] NOTE 2: When one of the two UEs acts as an IPv6 router (as described in Section 5.5.1.1) and the IP address / prefix also needs to be changed, the corresponding address configuration procedure shall be carried out after the link identifier update procedure.

[0194] 2. After receiving the Link Identifier Update Request message, UE-2 changes its identifier. UE-2 responds with a Link Identifier Update Response message containing the new identifier to be used (including the new Layer 2 ID, security information, an optional new application layer ID, and an optional new IP address / prefix (if IP communication is used)). If security is configured for a unicast link, the new identifier will be encrypted to protect privacy. The Link Identifier Update Response message is sent using the old identifier. UE-2 continues to receive traffic with the old Layer 2 ID from UE-1 until UE-2 receives traffic with the new Layer 2 ID from UE-1. After sending the Link Identifier Update Response message, if UE-2 has data to send, UE-2 keeps sending data traffic to UE-1 using the old identifier until UE-2 receives a Link Identifier Update Confirm message from UE-1.

[0195] 3. After receiving the Link Identifier Update Response message, UE-1 responds with a Link Identifier Update Confirm message. The Link Identifier Update Confirm message contains the new identifier from UE-2, as received in the Link Identifier Update Response message. The Link Identifier Update Confirm message is sent using the old identifier. UE-1 continues to receive traffic with the old Layer 2 ID from UE-2 until UE-1 receives traffic with the new Layer 2 ID from UE-2.

[0196] 4. The ProSe layer of UE-1 passes the PC5 link identifier of the unicast link and the updated Layer 2 ID (i.e., the new Layer 2 ID for the source UE-1 and the new Layer 2 ID for the destination UE-2) down to the AS layer. This enables the AS layer to update the provided Layer 2 ID for the unicast link.

[0197] For this unicast link, UE-1 starts using its new identifier and UE-2's new identifier.

[0198] 5. After receiving the Link Identifier Update Confirm message, the ProSe layer of UE-2 passes the PC5 link identifier and the updated Layer 2 ID for the unicast link (i.e., the new Layer 2 ID for the source UE-2 and the new Layer 2 ID for the destination UE-1) down to the AS layer. This enables the AS layer to update the provided Layer 2 ID for the unicast link.

[0199] UE-2 starts using its new identifier and UE-1's new identifier for this unicast link.

[0200] NOTE 3: The security information in the above message also needs to be updated simultaneously with the Layer 2 ID. This is defined in TS 33.503

[29] .

[0201] […]

[0202] 6.4.3.4 Layer 2 Link Modification for Unicast Links

[0203] Figure 6 4.3.4-1 shows the Layer 2 link modification procedure for unicast links. This procedure is used to:

[0204] -Add a new PC5 QoS flow to an existing PC5 unicast link.

[0205] - This covers the case for adding a new PC5 QoS flow to an existing ProSe service as well as the case for adding a new PC5 QoS flow to a new ProSe service.

[0206] - Modify an existing PC5 QoS flow in an existing PC5 unicast link.

[0207] - This covers the case of modifying PC5 QoS parameters for an existing PC5 QoS flow.

[0208] - This also covers the case where an associated ProSe service is removed from an existing PC5 QoS flow and the case where a new ProSe service is associated with an existing PC5 QoS flow.

[0209] - Remove existing PC5 QoS flows in existing PC5 unicast links.

[0210] [3GPP TS 23.304 V18.2.0 entitled "Layer 2 Link Modification Procedure" Figure 6 .4.3.4-1 Reproduced as Figure 10 ]

[0211] 0. UE-1 and UE-2 have a unicast link established as described in Section 6.4.3.1.

[0212] 1. The ProSe application layer in UE-1 provides application information for PC5 unicast communication. The application information contains ProSe service information and the application layer ID of the initiating UE. The application layer ID of the target UE may be included in the application information. If UE-1 decides to reuse the existing PC5 unicast link, as specified in Section 5.3.4, and therefore decides to modify the unicast link established with UE-2, UE-1 sends a link modification request to UE-2.

[0213] The link modification request message contains:

[0214] a) Add a new PC5 QoS flow to an existing PC5 unicast link:

[0215] -QoS information: Information about the PC5 QoS flow to be added. For each PC5 QoS flow, there is the PFI, the corresponding PC5 QoS parameters (ie, PQI and conditionally other parameters such as MFBR / GFBR, etc.), and optionally an associated ProSe identifier.

[0216] -Optional PC5 QoS rules.

[0217] b) Modify the PC5 QoS flow in an existing PC5 unicast link:

[0218] -QoS information: Information about the PC5 QoS flow to be modified. For each PC5 QoS flow, it includes the PFI, the corresponding PC5 QoS parameters (ie, PQI and conditionally other parameters such as MFBR / GFBR, etc.), and optionally an associated ProSe identifier.

[0219] -Optional PC5 QoS rules.

[0220] c) Remove the PC5 QoS flow from the existing PC5 unicast link:

[0221] -PFI.

[0222] 2. UE-2 responds with a Link Modification Accept message.

[0223] The link modification acceptance message contains:

[0224] - For case a) and case b) described in step 1:

[0225] -QoS information: Information about the PC5 QoS flows requested by UE-1. For each PC5 QoS flow, it includes the PFI, corresponding PC5 QoS parameters (i.e., PQI and conditionally other parameters such as MFBR / GFBR, etc.), and optionally an associated ProSe identifier.

[0226] -Optional PC5 QoS rules.

[0227] The ProSe layer of each UE provides information about the unicast link modification to the AS layer, which enables the AS layer to update the context related to the modified unicast link.

[0228] […]

[0229] 6.4.3.7 Layer 2 Link Management over the PC5 Reference Point for 5G ProSe Inter-UE Relay

[0230] 6.4.3.7.1 Common part of Layer 2 link management over the PC5 reference point for 5G ProSe inter-UE relay

[0231] For 5G ProSe communication via 5G ProSe inter-UE relay as described in Section 6.7.1 and Section 6.7.2:

[0232] -The direct communication request message on the first hop PC5 reference point contains:

[0233] - User information ID of the source 5G ProSe UE: the identity of the source 5G ProSe UE requesting the relay operation (i.e., user information ID).

[0234] - User Information ID of 5G ProSe Inter-UE Relay: The identity of the Inter-UE Relay (i.e., User Information ID) provided to the source 5G ProSe end UE during the 5G ProSe Inter-UE Relay discovery procedure.

[0235] - User information ID of target 5G ProSe UE: the identity of the target 5G ProSe UE (i.e., user information ID) provided to the source 5G ProSe UE during the inter-UE relay discovery procedure.

[0236] - (Optional) Destination Layer 2 ID of the target 5G ProSe end UE: The unicast destination Layer 2 ID of the target 5G ProSe end UE determined by the source 5G ProSe end UE, as specified in Section 5.8.2.4.

[0237] -ProSe service information: information about the ProSe identifier requesting Layer 2 link establishment.

[0238] -RSC: Connectivity service requested by the source 5G ProSe UE and provided by the 5G ProSe inter-UE relay.

[0239] - Security information: information used to establish security for first-hop PC5 link establishment.

[0240] NOTE 1 Security information is defined by SA WG3.

[0241] The direct communication request message on the second hop PC5 reference point contains:

[0242] -User information ID of the source 5G ProSe UE.

[0243] -User information ID of the target 5G ProSe UE.

[0244] -User information ID relayed between 5G ProSe UEs.

[0245] -ProSe service information: information about the ProSe identifier.

[0246] -RSC: Connectivity service requested by the source 5G ProSe UE and provided by the 5G ProSe inter-UE relay.

[0247] - Security information: information used to establish security for establishing a second-hop PC5 link.

[0248] NOTE 2 Security information is defined by SA WG3.

[0249] The direct communication acceptance message on the second hop PC5 reference point contains:

[0250] -User information ID of the target 5G ProSe UE.

[0251] The direct communication acceptance message on the first hop PC5 reference point contains:

[0252] -User information ID of the target 5G ProSe UE.

[0253] -User information ID relayed between 5G ProSe UEs.

[0254] The link modification request message on the first-hop PC5 reference point contains:

[0255] - User information ID of target 5G ProSe UE: the identity of the target 5G ProSe UE provided to the source 5G ProSe UE during the inter-UE relay discovery procedure.

[0256] - (Optional) Destination Layer 2 ID of the target 5G ProSe end UE: The unicast destination Layer 2 ID of the target 5G ProSe end UE determined by the source 5G ProSe end UE, as specified in Section 5.8.2.4.

[0257] The link modification request message on the second-hop PC5 reference point contains:

[0258] -User information ID of the source 5G ProSe UE.

[0259] -User information ID of the target 5G ProSe UE.

[0260] The link modification accept message on the second-hop PC5 reference point contains:

[0261] -User information ID of the target 5G ProSe UE.

[0262] The Link Modification Accept message on the first-hop PC5 reference point contains:

[0263] -User information ID of the target 5G ProSe UE.

[0264] 6.4.3.7.2 Layer 2 Link Management over PC5 Reference Point for 5G ProSe Layer 2 Inter-UE Relay

[0265] For 5G ProSe communication via 5G ProSe layer 2 inter-UE relay as described in Section 6.7.2, the description in Section 6.4.3.7.1 applies.

[0266] The message contents over the PC5 reference point for unicast mode 5G ProSe direct communication described in Sections 6.4.3.1 to 6.4.3.5 are the same for end-to-end connections between peer 5G ProSe end UEs.

[0267] Editor's note: Whether LIU between peer-to-peer UEs has the same message content as direct PC5 LIU messages is for further study.

[0268] 6.4.3.7.3 Layer 2 Link Management over PC5 Reference Point for 5G ProSe Layer 3 Inter-UE Relay

[0269] For 5G ProSe communication via 5G ProSe layer 3 inter-UE relay as described in Section 6.7.1, the description in Section 6.4.3.7.1 applies with the following differences and clarifications:

[0270] -In the security procedure of the first-hop PC5 reference point, the source 5G ProSe Layer 3 UE provides the 5G ProSe Layer 3 inter-UE relay with the IP address configuration or the link-local IPv6 address and QoS information of end-to-end QoS. If the PC5 link is used to convey Ethernet traffic, the source 5G ProSe Layer 3 UE provides its Ethernet MAC address instead of IP-related information.

[0271] -In the security procedure of the second-hop PC5 reference point, the 5G ProSe layer 3 inter-UE relay provides the target 5G ProSe end UE with IP address configuration or link-local IPv6 address and QoS information of the second-hop QoS. If the PC5 link is used to deliver Ethernet services, the 5G ProSe layer 3 inter-UE relay provides the Ethernet MAC address of the source 5G ProSe layer 3 end UE instead of IP-related information.

[0272] -The Direct Communication Accept message over the second-hop PC5 reference point additionally contains the IP address configuration or link-local IPv6 address and QoS information for the second-hop QoS. If the PC5 link is used to deliver Ethernet services, the target 5G ProSe Layer 3 UE provides its Ethernet MAC address instead of IP related information.

[0273] - Taking into account the received second-hop QoS, the 5G ProSe layer 3 inter-UE relay determines the QoS information of the first-hop QoS, and the direct communication accept message over the first-hop PC5 reference point additionally includes the IP address configuration or link-local IPv6 address, the QoS information of the first-hop QoS, and may include the IP address of the target 5G ProSe end UE. If the PC5 link is used to deliver Ethernet traffic, the 5G ProSe layer 3 inter-UE relay provides the Ethernet MAC address of the target 5G ProSe layer 3 end UE instead of IP-related information.

[0274] - In the Link Modification Request message over the first-hop PC5 reference point, the source 5G ProSe UE additionally includes QoS information for end-to-end QoS. If the PC5 link is used to deliver Ethernet services, the source 5G ProSe Layer 3 UE may provide its Ethernet MAC address.

[0275] - In the Link Modification Request message over the second-hop PC5 reference point, the 5G ProSe Layer 3 Inter-UE Relay additionally includes the second-hop QoS information to the target 5G ProSe end UE. If the PC5 link is used to deliver Ethernet traffic, the 5G ProSe Layer 3 Inter-UE Relay provides the Ethernet MAC address of the source 5G ProSe Layer 3 end UE.

[0276] -The Link Modification Accept message on the second-hop PC5 reference point additionally contains the QoS information of the second-hop QoS. If the PC5 link is used to deliver Ethernet services, the target 5G ProSe Layer 3 UE may provide its Ethernet MAC address.

[0277] - Taking into account the received second-hop QoS, the 5G ProSe Layer 3 Inter-UE Relay determines the QoS information for the first-hop QoS. The Link Modification Accept message over the first-hop PC5 reference point additionally contains the QoS information for the first-hop QoS and may include the IP address of the target 5G ProSe-side UE. If the PC5 link is used to deliver Ethernet traffic, the 5G ProSe Layer 3 Inter-UE Relay provides the Ethernet MAC address of the target 5G ProSe Layer 3-side UE instead of IP-related information.

[0278] When the PC5 link between the 5G ProSe layer 3 end UE and the 5G ProSe layer 3 inter-UE relay is released, the 5G ProSe layer 3 inter-UE relay can initiate the release of the PC5 link to the peer 5G ProSe layer 3 end UE, or notify the peer 5G ProSe layer 3 end UE that the peer PC5 link is released.

[0279] 6.4.3.7.4 Layer 2 Link Management over PC5 Reference Point for 5G ProSe Inter-UE Relay Communication with Integrated Discovery

[0280] This section is for 5G ProSe inter-UE relay communication integrated with the discovery procedure, as described in Section 6.7.3.

[0281] The direct communication request message on the first hop PC5 reference point contains:

[0282] -User information ID of the source 5G ProSe UE.

[0283] - (Optional) User Information ID of the target 5G ProSe UE: the identity of the target 5G ProSe UE (if provided by the ProSe application layer).

[0284] - (Optional) Destination Layer 2 ID of the target 5G ProSe end UE: The unicast destination Layer 2 ID of the target 5G ProSe end UE determined by the source 5G ProSe end UE, as specified in Section 5.8.2.4.

[0285] -ProSe service information: information about the ProSe identifier requesting Layer 2 link establishment.

[0286] -RSC: Connectivity service requested by the source 5G ProSe UE and provided by the 5G ProSe inter-UE relay.

[0287] -Relay_indication: indicates whether the direct communication request message can be forwarded by the 5G ProSe inter-UE relay.

[0288] - Security information: information used to establish security for first-hop PC5 link establishment.

[0289] NOTE 1 Security information is defined by SA WG3.

[0290] The direct communication request message on the second hop PC5 reference point contains:

[0291] -User information ID of the source 5G ProSe UE.

[0292] -User information ID relayed between 5G ProSe UEs.

[0293] -(Optional) User information ID of the target 5G ProSe UE.

[0294] -ProSe service information: information about the ProSe identifier.

[0295] -RSC: Connectivity service requested by the source 5G ProSe UE and provided by the 5G ProSe inter-UE relay.

[0296] - Security information: information used to establish security for establishing a second-hop PC5 link.

[0297] NOTE 2 Security information is defined by SA WG3.

[0298] The direct communication acceptance message on the second hop PC5 reference point contains:

[0299] -User information ID of the target 5G ProSe UE.

[0300] The direct communication acceptance message on the first hop PC5 reference point contains:

[0301] -User information ID of the target 5G ProSe UE.

[0302] -User information ID relayed between 5G ProSe UEs.

[0303] For 5G ProSe communication via 5G ProSe layer 3 inter-UE relay, additional explanations are as follows:

[0304] -In the security procedure of the second-hop PC5 reference point, the 5G ProSe layer 3 inter-UE relay provides the IP address configuration or link-local IPv6 address to the target 5G ProSe end UE.

[0305] - The Direct Communication Accept message over the second-hop PC5 reference point additionally includes the IP address configuration or link-local IPv6 address (if IP communication is used) and the Ethernet MAC address of the target 5G ProSe UE (if Ethernet communication is used). QoS information is not included in the security procedures or Direct Communication Accept message over the second-hop PC5 reference point.

[0306] -In the security procedure of the first-hop PC5 reference point, the source 5G ProSe end UE provides the IP address configuration, link-local IPv6 address and QoS information of end-to-end QoS to the 5G ProSe layer 3 inter-UE relay.

[0307] -5G ProSe Layer 3 Inter-UE Relay uses Layer 2 Link Modification to provide QoS information of the second-hop QoS to the target 5G ProSe end UE, as described in Section 6.4.3.4.

[0308] - Considering the second-hop QoS received from the target 5G ProSe side UE, the 5G ProSe layer 3 inter-UE relay determines the QoS information of the first-hop QoS. The direct communication accept message on the first-hop PC5 reference point additionally includes the IP address configuration or link-local IPv6 address, the QoS information of the first-hop QoS, and may include the IP address of the target 5G ProSe side UE (if IP communication is used) or the Ethernet MAC address of the target 5G ProSe side UE (if Ethernet communication is used).

[0309] For 5G ProSe communication via 5G ProSe layer 2 inter-UE relay, the message contents over the PC5 reference point for unicast mode 5G ProSe direct communication described in Sections 6.4.3.1 to 6.4.3.5 are the same for end-to-end connections between peer 5G ProSe end UEs.

[0310] […]

[0311] 6.7 5G ProSe Inter-UE Relay Communication

[0312] 6.7.1 5G ProSe Communication via 5G ProSe Layer 3 Inter-UE Relay

[0313] 6.7.1.1 Layer 2 Link Establishment for PC5 Communication via 5G ProSe Layer 3 Inter-UE Relay

[0314] Figure 6 .7.1.1-1 shows the procedure for Layer 2 link establishment via 5G ProSe Layer 3 Inter-UE Relay.

[0315] [3GPP TS 23.304 V18.2.0 titled "Layer 2 link establishment via 5G ProSe Layer 3 inter-UE relay" Figure 6 .7.1.1-1 Reproduced as Figure 11 ]

[0316] 1. Perform service authorization and provisioning for the source 5G ProSe Layer 3 UE, the target 5G ProSe Layer 3 UE, and the 5G ProSe Layer 3 Inter-UE Relay as described in Section 6.2.

[0317] 2. The source 5G ProSe layer 3 UE performs discovery of 5G ProSe layer 3 inter-UE relays as described in Section 6.3.2.4.

[0318] 3. The source 5G ProSe Layer 3 UE sends a Direct Communication Request message to initiate a unicast Layer 2 link establishment procedure with the 5G ProSe Layer 3 Inter-UE Relay. The parameters included in the Direct Communication Request message are described in Section 6.4.3.7.

[0319] The source layer 2 ID of the direct communication request message is self-assigned by the source 5G ProSe layer 3 end UE, and the destination layer 2 ID is set to the source layer 2 ID of the discovery message relayed between 5G ProSe layer 3 UEs.

[0320] 4. If the User Information ID of the 5G ProSe Layer 3 Inter-UE Relay in the Direct Communication Request message matches the User Information ID of the 5G ProSe Inter-UE Relay, and the RSC in the Direct Communication Request message matches one of the RSCs supported by the relay, the 5G ProSe Layer 3 Inter-UE Relay responds by establishing security with the source 5G ProSe Layer 3 UE. When security protection is enabled, the source 5G ProSe Layer 3 UE sends the parameters described in Section 6.4.3.7 to the 5G ProSe Layer 3 Inter-UE Relay.

[0321] If the Ethernet MAC address of the source 5G ProSe layer 3 UE is already used by another 5G ProSe layer 3 UE, the 5G ProSe layer 3 inter-UE relay may send a message to the source 5G ProSe layer 3 UE indicating that there is an Ethernet MAC address conflict.

[0322] The source Layer 2 ID used for the security establishment procedure is self-assigned by the 5G ProSe Layer 3 Inter-UE Relay, and the destination Layer 2 ID is set to the source Layer 2 ID of the received direct communication request message.

[0323] 5G ProSe layer 3 inter-UE relay will select different source layer 2 IDs for PC5 links for different types of services, i.e., IP services, Ethernet services, and unstructured services.

[0324] If the PC5 link is used to deliver unstructured traffic, the 5G ProSe layer 3 inter-UE relay will select different source layer 2 IDs for different pairs of source and target 5G ProSe layer 3 end UEs.

[0325] After receiving the security establishment procedure message, the source 5G ProSe layer 3 end UE obtains the layer 2 ID of the 5G ProSe layer 3 inter-UE relay for future communications, thereby being used for signaling and data services of this unicast link.

[0326] 5. After the security establishment procedure in step 4 is completed, the 5G ProSe Layer 3 Inter-UE Relay sends a Direct Communication Request message to initiate the unicast Layer 2 link establishment procedure with the target 5G ProSe Layer 3 UE. The parameters included in the Direct Communication Request message are described in Section 6.4.3.7.

[0327] The source layer 2 ID of the direct communication request message is self-assigned by the 5G ProSe layer 3 inter-UE relay, and the destination layer 2 ID is the unicast layer 2 ID of the target 5G ProSe layer 3 end UE associated with the user information ID of the target 5G ProSe layer 3 end UE.

[0328] 5G ProSe layer 3 inter-UE relay will select different source layer 2 IDs for PC5 links for different types of services, i.e., IP services, Ethernet services, and unstructured services.

[0329] If the PC5 link is used to deliver unstructured traffic, the 5G ProSe layer 3 inter-UE relay will select different source layer 2 IDs for different pairs of source and target 5G ProSe layer 3 end UEs.

[0330] 6. If the user information ID of the target 5G ProSe Layer 3 UE and the RSC included in the direct communication request match the user information ID of the target UE and the RSC supported by the target UE, the target 5G ProSe Layer 3 UE responds by establishing security with the 5G ProSe Layer 3 Inter-UE Relay. When security protection is enabled, the 5G ProSe Layer 3 Inter-UE Relay sends the parameters described in Section 6.4.3.7 to the target 5G ProSe Layer 3 UE.

[0331] The source layer 2 ID used for the security establishment procedure is self-assigned by the target 5G ProSe layer 3 end UE, and the destination layer 2 ID is set to the source layer 2 ID of the received direct communication request message.

[0332] After receiving the security establishment procedure message, the 5G ProSe layer 3 inter-UE relay obtains the layer 2 ID of the target 5G ProSe layer 3 end UE for future communications, thereby being used for signaling and data services of this unicast link.

[0333] 7. The target 5G ProSe Layer 3 UE sends a Direct Communication Accept message to the 5G ProSe Layer 3 Inter-UE Relay for which security has been successfully established. The parameters included in the Direct Communication Accept message are described in Section 6.4.3.7.

[0334] 8. For IP services, allocate an IPv6 prefix or IPv4 address to the target 5G ProSe Layer 3 UE, as defined in Section 5.5.1.4.

[0335] 9. After receiving the Direct Communication Accept message from the target 5G ProSe Layer 3 UE, the 5G ProSe Layer 3 Inter-UE Relay sends a Direct Communication Accept message to the source 5G ProSe Layer 3 UE for which security has been successfully established. The parameters included in the Direct Communication Accept message are described in Section 6.4.3.7.

[0336] 10. For IP services, an IPv6 prefix or IPv4 address is allocated to the source 5G ProSe layer 3 UE, as defined in Section 5.5.1.4.

[0337] 11. For IP communication, the 5G ProSe layer 3 inter-UE relay may store the association between the user information ID and the IP address of the target 5G ProSe layer 3 end UE in its DNS entry, and the 5G ProSe layer 3 inter-UE relay may act as a DNS server for other UEs. If the IP address of the target 5G ProSe layer 3 end UE is not received in step 9, then after step 10, the source 5G ProSe layer 3 end UE may send a DNS query to the 5G ProSe layer 3 inter-UE relay to request the IP address of the target 5G ProSe layer 3 end UE, and the 5G ProSe layer 3 inter-UE relay returns the IP address of the target 5G ProSe layer 3 end UE to the source 5G ProSe layer 3 end UE.

[0338] For Ethernet communication, the 5G ProSe layer 3 inter-UE relay maintains the association between the PC5 link and the Ethernet MAC address received from the 5G ProSe layer 3 end UE.

[0339] For unstructured traffic communications, for each pair of source and target 5G ProSe layer 3 end UEs, the 5G ProSe layer 3 inter-UE relay maintains a 1:1 mapping between the PC5 link with the source 5G ProSe layer 3 end UE and the PC5 link with the target 5G ProSe layer 3 end UE.

[0340] 12. The source 5G ProSe layer 3 end UE communicates with the target 5G ProSe layer 3 end UE via the 5G ProSe layer 3 inter-UE relay.

[0341] In the case where a source 5G ProSe layer 3 UE communicates with multiple target 5G ProSe layer 3 UEs, the PC5 link between the source 5G ProSe layer 3 UE and the 5G ProSe layer 3 inter-UE relay can be shared by multiple target 5G ProSe layer 3 UEs for each RSC, while a separate PC5 link can be established between the 5G ProSe layer 3 inter-UE relay and the target 5G ProSe layer 3 UE for each RSC. For the shared PC5 link, the Layer 2 link modification procedure will be used.

[0342] In the case where multiple source 5G ProSe layer 3 UEs communicate with one target 5G ProSe layer 3 UE, the PC5 link between the 5G ProSe layer 3 inter-UE relay and the target 5G ProSe layer 3 UE can be shared for each RSC, while a separate PC5 link can be established between the source 5G ProSe layer 3 UE and the 5G ProSe layer 3 inter-UE relay for each RSC. For the shared PC5 link, the layer 2 link modification procedure will be used.

[0343] […]

[0344] 6.7.1.4 Layer 2 Link Modification for PC5 Communication via 5G ProSe Layer 3 Inter-UE Relay

[0345] Figure 6 7.1.4-1 shows the Layer 2 Link Modification procedure via Layer 3 Inter-UE Relay. This procedure is used to add / modify / remove PC5 QoS flows in an existing PC5 unicast link, as described in Section 6.4.3.7.3.

[0346] [3GPP TS 23.304 V18.2.0 entitled "Layer 2 Link Modification Procedure via Layer 3 Inter-UE Relay" Figure 6 .7.1.4-1 Reproduced as Figure 12 ]

[0347] 0. Unicast links are established between UE-1 and the inter-UE relay, and between the inter-UE relay and UE-2, as described in Section 6.7.1.1.

[0348] 1. UE-1 sends a Link Modification Request to the Inter-UE Relay as described in Section 6.4.3.7.3.

[0349] 2. After receiving the Link Modification Request message from UE-1, the Inter-UE Relay sends a Link Modification Request to UE-2, as described in Section 6.4.3.7.3.

[0350] 3. UE-2 responds to the Inter-UE Relay with a Link Modification Accept message as described in section 6.4.3.7.3.

[0351] 4. After receiving the Link Modification Accept message from UE-2, the Inter-UE Relay responds with a Link Modification Accept message to UE-1 as described in Section 6.4.3.7.3.

[0352] […]

[0353] 6.7.2 5G ProSe Communication via 5G ProSe Layer 2 Inter-UE Relay

[0354] This app is applicable to 5G ProSe layer 2 inter-UE relay.

[0355] [3GPP TS 23.304 V18.2.0 titled "5G ProSe communication via 5G ProSe layer 2 inter-UE relay" Figure 6 .7.2 -1 reproduced as Figure 13 ]

[0356] This procedure has been preceded by service authorization and provisioning for the 5G ProSe layer 2 inter-UE relay and the 5G ProSe end UE, as described in Section 6.2.

[0357] 1. Model A or Model B 5G ProSe inter-UE relay discovery as described in Section 6.3.2.4 is performed, and the source 5G ProSe UE selects an appropriate 5G ProSe layer 2 inter-UE relay for communicating with the target 5G ProSe UE.

[0358] 2. The source 5G ProSe UE decides whether to use the existing PC5 link with the 5G ProSe Inter-UE Relay to obtain the required service. If the existing PC5 link is used, the Layer 2 Link Modification procedure as specified in Section 6.4.3.7 is used towards the 5G ProSe Inter-UE Relay. Otherwise, the Layer 2 Link Establishment procedure is used towards the 5G ProSe Inter-UE Relay.

[0359] This procedure is towards the selected 5G ProSe Inter-UE Relay and for Layer 2 link establishment, security establishment is performed before initiating step 3.

[0360] 3.5G ProSe Layer 2 Inter-UE Relay decides whether to use the existing PC5 link between the 5G ProSe Inter-UE Relay and the target 5G ProSe end UE to obtain the required service, and initiates the Layer 2 link establishment procedure or Layer 2 link modification procedure as specified in Section 6.4.3.7 with the target 5G ProSe end UE.

[0361] This procedure is performed using a unicast Layer 2 ID towards the target 5G ProSe UE.

[0362] After step 3 is completed, the 5G ProSe layer 2 inter-UE relay sends a direct communication accept message or a link modification accept message to the source 5G ProSe end UE.

[0363] 4. The source 5G ProSe UE establishes an end-to-end connection for unicast mode communication with the target 5G ProSe UE, as described in Section 6.4.3.7.

[0364] Data is transferred between the source 5G ProSe UE and the target 5G ProSe UE via the 5G ProSe layer 2 inter-UE relay. The 5G ProSe layer 2 inter-UE relay forwards all data messages between the source 5G ProSe UE and the target 5G ProSe UE as specified in TS 38.300

[12] .

[0365] 6.7.3 5G ProSe Inter-UE Relay Communication with Integrated Discovery

[0366] 6.7.3.1 Overview

[0367] Supports 5G ProSe communication via 5G ProSe inter-UE relay with integrated discovery.

[0368] For 5G ProSe inter-UE relay communication integrated with discovery, when a UE allows direct communication requests to other UEs involving inter-UE relay, the UE indicates this by including relay_indication in the broadcast direct communication request message.

[0369] When the inter-UE relay receives a direct communication request containing relay_indication, it decides whether to forward the message based on, for example, the relay service code (if present), application ID, operator policy for each relay service code, signal strength, and local policy.

[0370] 6.7.3.2 Procedures for Communication via Layer 3 Inter-UE Relay

[0371] [3GPP TS 23.304 V18.2.0 entitled "5G ProSe Inter-UE Relay Communication with Integrated Discovery via Layer 3 Inter-UE Relay" Figure 6 .7.3.2-1 Reproduced as Figure 14 ]

[0372] 0.5G ProSe end UEs are authorized and provisioned with parameters to use services provided by 5G ProSe inter-UE relays. 5G ProSe inter-UE relays are authorized and provisioned with parameters to provide services of relaying traffic among 5G ProSe end UEs.

[0373] 1. The source 5G ProSe UE (i.e., UE-1) wants to establish unicast communication with the target 5G ProSe UE (i.e., UE-2) and broadcasts a direct communication request. The parameters included in the direct communication request message are described in Section 6.4.3.7.

[0374] The relay_indication in the direct communication request is used to indicate whether the 5G ProSe inter-UE relay can forward the direct communication request message. It is also used to limit the number of hops of the 5G ProSe inter-UE relay by removing the relay_indication in the direct communication request message from the 5G ProSe inter-UE relay.

[0375] The source layer 2 ID and destination layer 2 ID for the direct communication request message are defined in section 5.8.5.

[0376] NOTE 1: The data type of relay_indication can be determined in phase 3.

[0377] 2. Upon receiving a direct communication request with relay_indication from UE-1, the 5G ProSe inter-UE relays (i.e., Relay-1 and Relay-2) may decide to participate in the procedure and broadcast a direct communication request message without relay_indication in their vicinity. The parameters included in the direct communication request message are described in Section 6.4.3.7.

[0378] The source layer 2 ID and destination layer 2 ID for the direct communication request message are defined in section 5.8.5.

[0379] 3. When UE-2 receives a direct communication request from one or more 5G ProSe inter-UE relays, UE-2 selects a 5G ProSe inter-UE relay to which UE-2 will respond. UE-2 may select a 5G ProSe inter-UE relay based on, for example, signal strength, local policy, and operator policy (if any) for each relay service code.

[0380] 4. If required, security establishment occurs between UE-2 and the selected 5G ProSe Inter-UE Relay (here Relay-1).

[0381] If an existing PC5 link can be reused, then Link Modify Request and Link Modify Accept messages are used.

[0382] NOTE 2: Conflicts between link modification requests and direct communication requests may be determined in Phase 3.

[0383] 5. UE-2 replies with a direct communication accept message to relay-1. The parameters included in the direct communication accept message are described in Section 6.4.3.7.

[0384] 6. For IP services, allocate an IPv6 prefix or IPv4 address to the target 5G ProSe Layer 3 UE, as defined in Section 5.5.1.4.

[0385] 7. If required, security establishment occurs between UE-1 and Relay-1.

[0386] 8. For 5G ProSe inter-UE relay communication integrated with discovery, after receiving the QoS information of end-to-end QoS from UE-1, Relay-1 provides QoS information of second-hop QoS to UE-2 using a Link Modification Request message.

[0387] 9. For 5G ProSe inter-UE relay communication with integrated discovery, UE-2 responds with a Link Modification Accept message.

[0388] 10. Relay-1 responds to UE-1 with a Direct Communication Accept message. The parameters included in the Direct Communication Accept message are described in Section 6.4.3.7.

[0389] 11. For IP services, an IPv6 prefix or IPv4 address is allocated to the source 5G ProSe layer 3 UE, as defined in Section 5.5.1.4.

[0390] 12. For IP communication, the 5G ProSe layer 3 inter-UE relay may store the association between the user information ID and the IP address of the target 5G ProSe layer 3 end UE in its DNS entry, and the 5G ProSe layer 3 inter-UE relay may act as a DNS server for other UEs. If the IP address of the target 5G ProSe layer 3 end UE is not received in step 10, then after step 11, the source 5G ProSe layer 3 end UE may send a DNS query to the 5G ProSe layer 3 inter-UE relay to request the IP address of the target 5G ProSe layer 3 end UE, and the 5G ProSe layer 3 inter-UE relay returns the IP address of the target 5G ProSe layer 3 end UE to the source 5G ProSe layer 3 end UE.

[0391] For Ethernet communication, the 5G ProSe Layer 3 inter-UE relay acts as an Ethernet switch by maintaining the association between the PC5 link and the Ethernet MAC address received from the 5G ProSe Layer 3 end UE.

[0392] For unstructured traffic communications, for each pair of source and target 5G ProSe layer 3 end UEs, the 5G ProSe layer 3 inter-UE relay maintains a 1:1 mapping between the PC5 link with the source 5G ProSe layer 3 end UE and the PC5 link with the target 5G ProSe layer 3 end UE.

[0393] The source 5G ProSe layer 3 end UE communicates with the target 5G ProSe layer 3 end UE via a 5G ProSe layer 3 inter-UE relay.

[0394] 6.7.3.3 Procedures for Communication via Layer 2 Inter-UE Relay

[0395] [3GPP TS 23.304 V18.2.0 entitled “5G ProSe inter-UE relay communication with integrated discovery via Layer 2 inter-UE relay” Figure 6 .7.3.3 -1 Reproduced as Figure 15 ]

[0396] Step 0-Step 5 and Figure 6 .7.3.2-1 steps 0 to 5 are the same. Step 6 is the same as Figure 6 Same as step 7 of .7.3.2-1.

[0397] Step 7 and Figure 6 The parameters contained in the message are described in Section 6.4.3.7.

[0398] 8. For 5G ProSe inter-UE relay communication via Layer 2 inter-UE relay, UE-1 establishes an end-to-end connection for unicast mode communication with UE-2 as described in Section 6.4.3.7.

[0399] Editor's Note: Any additional updates on procedures via Layer 2 Inter-UE Relay, such as those based on RAN decisions, will be included here.

[0400] 3GPP TS24.554 introduces the following:

[0401] 7.2.2 5G ProSe Direct Link Establishment Procedure

[0402] 7.2.2.1 Overview

[0403] Depending on the type of 5G ProSe direct link establishment procedure (i.e., UE-oriented Layer 2 link establishment or ProSe service-oriented Layer 2 link establishment in 3GPP TS 23.304 [2]), the 5G ProSe direct link establishment procedure is used to establish a 5G ProSe direct link between two UEs, or to establish multiple 5G ProSe direct links between a UE and multiple target UEs. The UE that sends the request message is called the "initiating UE" and the other UEs are called "target UEs". If the request message does not indicate a specific target UE (i.e., target user information is not included in the request message) and multiple target UEs are interested in the ProSe application indicated in the request message, the initiating UE shall process the corresponding response messages received from those target UEs. The maximum number of 5G ProSe direct links established in a UE at any one time shall not exceed the implementation-specific maximum number of established 5G ProSe direct links.

[0404] NOTE 1: The recommended maximum number of established 5G ProSe direct links is 8.

[0405] When the 5G ProSe direct link establishment procedure for the 5G ProSe Layer 3 remote UE is successfully completed, and if there is a PDU session established for relaying the traffic of the 5G ProSe remote UE, the 5G ProSe Layer 3 UE to network relay UE shall perform the remote UE reporting procedure as specified in 3GPP TS 24.501

[11] .

[0406] NOTE 2: A single PC5 unicast link is established between the 5G ProSe Layer 2 UE to network relay UE and the 5G ProSe Layer 2 remote UE to support the PDU session of the 5G ProSe Layer 2 remote UE, as specified in 3GPP TS 38.300

[21] .

[0407] 7.2.2.2 5G ProSe Direct Link Establishment Procedure Initiated by the Initiating UE

[0408] The initiating UE shall meet the following prerequisites before initiating this procedure:

[0409] a) A request from an upper layer to transmit a data packet for a ProSe application via PC5, or a request from a lower layer to trigger the establishment of a ProSe direct link;

[0410] b) the communication mode is unicast mode (e.g., pre-configured as specified in Section 5.2.4 or indicated by upper layers);

[0411] c) the link layer identifier for the initiating UE (i.e., Layer 2 ID for unicast communication) is available (e.g., pre-configured or self-assigned) and is not used by other existing 5G ProSe direct links within the initiating UE;

[0412] d) the link layer identifier for the destination UE (i.e., the unicast Layer 2 ID or broadcast Layer 2 ID of the target UE) is available to the initiating UE (e.g., pre-configured, obtained as specified in section 5.2, known via previous ProSe direct communication, or indicated by lower layers);

[0413] NOTE 1: In the case where different ProSe applications are mapped to different preset destination Layer 2 IDs, when the originating UE wishes to establish a single unicast link that can be used for more than one ProSe identifier, the UE may select any of the preset destination Layer 2 IDs for unicast initial signaling.

[0414] e) The initiating UE is authorized for 5G ProSe direct communication on PC5 of NR-PC5 in the serving PLMN, has a valid authorization for 5G ProSe direct communication on PC5 in NR-PC5 when not served by NG-RAN, is authorized to use a 5G ProSe UE to network relay UE, is authorized to use a 5G ProSe inter-UE relay UE or is authorized to act as a 5G ProSe inter-UE relay UE. The UE considers that it is not served by NG-RAN if the following conditions are met:

[0415] 1) Not served by NG-RAN for ProSe direct communication on PC5;

[0416] 2) in the limited service state as specified in 3GPP TS 23.122

[14] , provided that the reason why the UE is in the limited service state is one of the following;

[0417] i) The UE cannot find a suitable cell in the selected PLMN, as specified in 3GPP TS 38.304

[15] ;

[0418] ii) the UE receives a REGISTRATION REJECT message or SERVICE REJECT message with 5GMM cause #11 “PLMN not allowed” as specified in 3GPP TS 24.501

[11] ; or

[0419] iii) the UE receives a REGISTRATION REJECT message or SERVICE REJECT message with 5GMM cause #7 “5GS service not allowed” as specified in 3GPP TS 24.501

[11] ; or

[0420] 3) is in a limited service state as specified in 3GPP TS 23.122

[14] for reasons other than i), ii) or iii) above and is located in a geographical area where the UE has “non-operator managed” radio parameters as specified in section 5.2;

[0421] Editor's note: The 5G ProSe direct link establishment procedure is used for direct communication between a 5G ProSe UE and a 5G ProSe inter-UE relay UE. The characteristics of the UE in the limited service state need to be re-discussed, which will be determined by SA2.

[0422] f) There is no existing 5G ProSe direct link for a pair of peer application layer IDs, or there is an existing 5G ProSe direct link for a pair of peer application layer IDs, and:

[0423] 1) The network layer protocol of the existing 5G ProSe direct link is different from the network layer protocol required by the upper layer for this ProSe application in the initiating UE;

[0424] 2) The security policy (signaling security policy or user plane security policy) corresponding to the ProSe identifier is not compatible with the security policy of the existing 5G ProSe direct link; or

[0425] 3) In case the 5G ProSe direct link establishment procedure is used for direct communication between a 5G ProSe Layer 3 remote UE and a 5G ProSe Layer 3 UE to a network relay UE, an existing 5G ProSe direct link for peer UEs is established with a different RSC, or is established but not used for direct communication between a 5G ProSe Layer 3 remote UE and a 5G ProSe Layer 3 UE to a network relay UE;

[0426] 4) in case the 5G ProSe direct link establishment procedure is used for direct communication between a 5G ProSe Layer 2 remote UE and a 5G ProSe Layer 2 UE to a relay UE of the network, an existing 5G ProSe direct link for peer UEs is established but not used for direct communication between the 5G ProSe Layer 2 remote UE and the 5G ProSe Layer 2 UE to a relay UE of the network; or;

[0427] 5) In case the 5G ProSe direct link establishment procedure is used for direct communication between a 5G ProSe layer 3 end UE and a 5G ProSe layer 3 inter-UE relay UE, the existing 5G ProSe direct link for peer UEs is established with a different RSC, or is established but not used for direct communication between the 5G ProSe layer 3 end UE and the 5G ProSe layer 3 inter-UE relay UE;

[0428] g) the number of established 5G ProSe direct links is less than the implementation-specific maximum number of established 5G ProSe direct links allowed in the UE at any one time;

[0429] h) Timer T5088 is not associated with the link layer identifier of the destination UE or timer T5088 associated with the link layer identifier of the destination UE has expired or stopped.

[0430] i) in the case that: the UE acts as a 5G ProSe layer 3 inter-UE relay UE, a 5G ProSe direct link modification procedure is initiated on an existing 5G ProSe direct link for direct communication between the 5G ProSe layer 3 end UE and the 5G ProSe layer 3 inter-UE relay UE, and there is no existing 5G ProSe direct link between the 5G ProSe layer 3 inter-UE relay UE and an additional target 5G ProSe layer 3 end UE, a ProSe direct link modification request message is received from the 5G ProSe layer 3 end UE to establish 5G ProSe inter-UE relay communication with the additional 5G ProSe layer 3 end UE, as specified in section 7.2.3.2; and

[0431] j) The initiating UE has received a ProSe direct link establishment request message including a relay indication, and the initiating UE acts as a 5G ProSe inter-UE relay UE. The 5G ProSe direct link establishment procedure is used for direct communication between the 5G ProSe inter-UE relay UE and the 5G ProSe end UE.

[0432] After receiving service data or request from upper layers, the initiating UE shall derive PC5 QoS parameters and assign a PQFI for the established PC5 QoS flow as specified in section 7.2.7.

[0433] If the 5G ProSe direct link establishment procedure is used for direct communication between a 5G ProSe remote UE and a 5G ProSe UE-to-network relay UE, the UE shall apply DUCK or DUSK with the associated encrypted bitmask for UE-to-network relay discovery and a UTC-based counter for encryption:

[0434] a) Relay service code; and

[0435] b) UP-PRUK ID or CP-PRUK ID (if applicable),

[0436] As specified in section 6.3.5.2 of 3GPP TS 33.503

[34] , the UE shall use the security-protected relay service code and the security-protected UP-PRUK ID or the security-protected CP-PRUK ID to create the ProSe Direct Link Setup Request message.

[0437] NOTE 2: If the UE is configured to use neither DUCK nor DUSK, the relay service code and UP-PRUK ID or CP-PRUK ID are not encrypted.

[0438] If the 5G ProSe direct link establishment procedure is used for direct communication between a 5G ProSe inter-UE relay UE and a target 5G ProSe end UE, if the initiating UE cannot identify an existing 5G ProSe direct link established between the initiating UE and the target UE after receiving the ProSe direct link establishment request message using integrated discovery (i.e., where the destination L2ID is set to the broadcast value as specified in section 5.2.4 and the relay indication is included), then the initiating UE acting as a 5G ProSe inter-UE relay UE initiates the 5G ProSe direct link establishment procedure to the target 5G ProSe end UE.

[0439] If the 5G ProSe direct link establishment procedure is used for direct communication between a 5G ProSe inter-UE relay UE and a target 5G ProSe end UE, then without integrated discovery, after successfully completing the 5G ProSe direct link security mode control procedure with the source 5G ProSe end UE, the initiating UE acting as the 5G ProSe inter-UE relay UE initiates the 5G ProSe direct link establishment procedure to the target 5G ProSe end UE.

[0440] Editor's note: When the direct link modification procedure can be used between a 5G ProSe inter-UE relay UE and a target 5G ProSe end UE is for further study.

[0441] To initiate the 5G ProSe direct link establishment procedure, the initiating UE will create a ProSe direct link establishment request message. The initiating UE:

[0442] a) contains source user information, which is set to the application layer ID of the originating UE received from upper layers, or to the user information ID of the source 5G ProSe UE when the 5G ProSe direct link establishment procedure is used for 5G ProSe direct communication between a 5G ProSe UE and a 5G ProSe inter-UE relay UE;

[0443] b) shall contain the ProSe identifier received from upper layers if the 5G ProSe direct link establishment procedure is not used for 5G ProSe direct communication between a 5G ProSe remote UE and a 5G ProSe UE to a network relay UE;

[0444] c) The target user information shall be included, which shall be set to the target UE's application layer ID if received from upper layers or known based on the target UE's unicast layer 2 ID (i.e., destination layer 2 ID) as described in section 5.8.2.4 of 3GPP TS 23.304 [3], to the 5G ProSe UE to network relay UE's user information ID obtained during the 5G ProSe UE to network relay discovery procedure, or to the target 5G ProSe end UE's user information ID:

[0445] 1) If the initiating UE acts as the source 5G ProSe UE and the user information ID of the target 5G ProSe UE is obtained during the 5G ProSe inter-UE relay discovery procedure; or

[0446] 2) If the initiating UE acts as a 5G ProSe inter-UE relay UE, and the user information ID of the target 5G ProSe UE is obtained in the ProSe direct link establishment request message or the ProSe direct link modification request message from the source 5G ProSe UE;

[0447] ca) The inter-UE relay UE user information including the user information ID set as the 5G ProSe inter-UE relay UE:

[0448] 1) If obtained during the 5G ProSe Inter-UE Relay Discovery procedure, and the 5G ProSe Direct Link Establishment procedure is used for 5G ProSe direct communication between the source 5G ProSe end UE and the 5G ProSe Inter-UE Relay UE; or

[0449] 2) If the originating UE acts as a 5G ProSe inter-UE relay UE and the user information ID is configured under the configuration parameters for 5G ProSe inter-UE relay, as specified in Section 5.2.7;

[0450] cb) if the originating UE acts as the source 5G ProSe UE and the layer 2 ID of the target 5G ProSe UE is available in the source 5G ProSe UE via previous direct communication, then the target UE layer 2 ID set to the layer 2 ID of the target 5G ProSe UE shall be included;

[0451] d) If the 5G ProSe direct link is not used for direct communication between the 5G ProSe remote UE and the 5G ProSe UE to network relay UE:

[0452] 1) If the UE PC5 unicast signaling integrity protection policy is set to "signaling integrity protection required" or "signaling integrity protection preferred", then the key establishment information container shall be included, and if the UE PC5 unicast signaling integrity protection policy is set to "signaling integrity protection not required", then the key establishment information container may be included;

[0453] NOTE 3: The key establishment information container is provided by the upper layer.

[0454] e) will include:

[0455] 1) Nonce_1, provided that direct communication is not between a 5G ProSe Remote UE and a 5G ProSe UE-to-network Relay UE, or provided that direct communication is between a 5G ProSe Remote UE and a 5G ProSe UE-to-network Relay UE and security procedures on the control plane are used as specified in 3GPP TS 33.503

[34] ;

[0456] 2)K NRP Freshness parameter 1, provided that direct communication is between a 5G ProSe Remote UE and a 5G ProSe UE to Network Relay UE and security procedures on the user plane are used as specified in 3GPP TS 33.503

[34] ;

[0457] If the UE PC5 unicast signaling integrity protection policy is set to "Signaling integrity protection required" or "Signaling integrity protection preferred", then set to a 128-bit nonce generated by the initiating UE for the purpose of session key establishment over this 5G ProSe direct link;

[0458] NOTE 4: The Nonce_1 IE in the ProSe Direct Link Setup Request message is used to store the value of Nonce_1 or K NRP Freshness parameter 1.

[0459] f) shall include its UE security capabilities, indicating the list of algorithms supported by the initiating UE for security establishment of this 5G ProSe direct link;

[0460] g) will contain the K selected by the initiating UE NRP-sess The MSB of the ID, as specified in 3GPP TS 33.503

[34] , provided that the UE PC5 unicast signaling integrity protection policy is set to "Signaling integrity protection required" or "Signaling integrity protection preferred";

[0461] NOTE 5: If the direct communication is not between a 5G ProSe remote UE and a 5G ProSe UE to a relay UE in the network, then K NRP-sessID remains corresponding to K NRP-sess If the direct communication is between a 5G ProSe remote UE and a 5G ProSe UE to a network relay UE, then K NRP-sess ID remains corresponding to K NRP-sess (if security procedures on the user plane are used) or K relay-sess The ID of the control plane security program (if using).

[0462] h) may contain K NRP ID, provided that the initiating UE has an existing K NRP , and direct communication is not between the 5G ProSe remote UE and the 5G ProSe UE to the network relay UE;

[0463] i) will include its UE PC5 unicast signaling security policy. In the case where different ProSe applications are mapped to different PC5 unicast signaling security policies, when the initiating UE wants to establish a single unicast link that can be used for more than one ProSe application, each signaling security policy of these ProSe applications should be compatible, for example, "signaling integrity protection not required" and "signaling integrity protection required" are incompatible. In the case where the 5G ProSe direct link establishment procedure is used for direct communication between a 5G ProSe remote UE and a 5G ProSe UE to a network relay UE, the signaling integrity protection policy will be set to "signaling integrity protection required";

[0464] j) containing the Relay Service Code IE, which is set to the Relay Service Code of the target relay UE when the 5G ProSe Direct Link Establishment Procedure is used for direct communication between a 5G ProSe remote UE and a 5G ProSe UE-to-network relay UE, or is set to the Relay Service Code indicating the connectivity service requested by the source 5G ProSe end UE when the 5G ProSe Direct Link Establishment Procedure is used for direct communication between a (source or target) 5G ProSe end UE and a 5G ProSe inter-UE relay UE;

[0465] k) containing a UTC-based counter LSB, which is set to the four least significant bits of the UTC-based counter in case the 5G ProSe direct link establishment procedure is used for direct communication between a 5G ProSe remote UE and a 5G ProSe UE to a network relay UE;

[0466] l) shall contain the UE Identity IE, which is set to the SUCI of the originating UE in the following cases:

[0467] 1) 5G ProSe direct link establishment procedure is used for direct communication between a 5G ProSe remote UE and a 5G ProSe UE to a relay UE of the network; and

[0468] 2) Security for relaying from a 5G ProSe UE to the network uses security procedures on the control plane and the originating UE does not have a valid CP-PRUK as specified in 3GPP TS 33.503

[34] , or security for relaying from a 5G ProSe UE to the network uses security procedures on the user plane and the originating UE does not have a valid UP-PRUK as specified in 3GPP TS 33.503

[34] ;

[0469] m) shall contain the User Security Key ID IE, which shall be set to:

[0470] 1) The UP-PRUK ID of the initiating UE, provided that:

[0471] i) The 5G ProSe direct link establishment procedure is used for direct communication between a 5G ProSe remote UE and a 5G ProSe UE to a relay UE in the network;

[0472] ii) the originating UE has a valid UP-PRUK; and

[0473] iii) security for 5G ProSe UE to network relay using security procedures on the user plane as specified in 3GPP TS 33.503

[34] ; or

[0474] 2) The CP-PRUK ID of the originating UE associated with the relay service code of the target UE, provided that:

[0475] i) The 5G ProSe direct link establishment procedure is used for direct communication between a 5G ProSe remote UE and a 5G ProSe UE to a relay UE in the network;

[0476] ii) the originating UE has a valid CP-PRUK associated with the target UE's relay service code; and

[0477] iii) Security for 5G ProSe UE to network relay uses security procedures on the control plane as specified in 3GPP TS 33.503

[34] ;

[0478] n) shall contain the HPLMN ID of the originating UE, provided that the UP-PRUK ID of the originating UE is included and is not in NAI format (see 3GPP TS 33.503

[34] );

[0479] o) shall include the MIC IE, which is set to the calculated MIC value in the case where the 5G ProSe Direct Link Establishment procedure is used for direct communication between a 5G ProSe Remote UE and a 5G ProSe UE-to-network Relay UE and the UE has a DUIK, as specified in section 6.3.5.3 of 3GPP TS 33.503

[34] ; and

[0480] p) shall include a relay indication indicating that the ProSe direct link establishment request message may be forwarded by a 5G ProSe inter-UE relay UE, provided that the 5G ProSe direct link establishment procedure is used for direct communication between the source 5G ProSe end UE and the 5G ProSe inter-UE relay UE;

[0481] Editor's note: Security parameters for 5G ProSe inter-UE relaying and parameters for 5G ProSe layer 2 inter-UE relaying are for further study.

[0482] After the ProSe Direct Link Setup Request message is generated, the initiating UE passes this message along with the source Layer 2 ID and the destination Layer 2 ID to the lower layers for transmission, as follows:

[0483] a) If the 5G ProSe direct communication is due to 5G ProSe direct discovery as defined in sections 6.2.14, 6.2.15, 8.2.1 and 8a.2.1:

[0484] self-assigned source layer 2 ID, and

[0485] 1) Destination Layer 2 ID, which is set to the target UE Layer 2 ID received in the ProSe Direct Link Setup Request message or the ProSe Direct Link Modify Request message from the source 5G ProSe UE, provided that the initiating UE acts as a 5G ProSe Inter-UE Relay UE;

[0486] 2) otherwise, set to the destination Layer 2 ID of the source Layer 2 ID in the received ProSe PC5 discovery message for the discovery procedure;

[0487] b) If the initiating UE acts as a source 5G ProSe end UE, and the 5G ProSe direct link establishment procedure is used for direct communication with integrated discovery between the source 5G ProSe end UE and a 5G ProSe interUE relay UE:

[0488] self-assigns a Source Layer 2 ID and sets the Destination Layer 2 ID to the configured Broadcast Destination Layer 2 ID as specified in Section 5.2.4; or

[0489] c) If the initiating UE acts as a 5G ProSe inter-UE relay UE, and the 5G ProSe direct link establishment procedure is used for direct communication with integrated discovery between the 5G ProSe inter-UE relay UE and the target 5G ProSe end UE:

[0490] Assign the source layer 2 ID yourself and set the destination layer 2 ID to:

[0491] 1) Target UE Layer 2 ID, if received in the ProSe Direct Link Setup Request message from the source 5G ProSe UE; otherwise

[0492] 2) a broadcast destination layer 2 ID configured as specified in section 5.2.4; or

[0493] d) Otherwise:

[0494] self-assigned Source Layer 2 ID and Destination Layer 2 ID set to the Destination Layer 2 ID used for unicast initial signaling as specified in Section 5.2.4,

[0495] NOTE 6: The UE implementation ensures that any value of the self-assigned source Layer-2 ID in a) and b) is different from any other self-assigned source Layer-2 ID used for 5G ProSe direct discovery as specified in sections 6.2.14, 6.2.15 and 8.2.1, and different from any other provided destination Layer-2 ID as specified in section 5.2.

[0496] NOTE 6A: The UE implementation ensures that any value of the self-assigned Source Layer 2 ID in a) and b) is different from any self-assigned Source Layer 2 ID when used for 5G ProSe direct communication with a data unit type different from the data unit type of the established 5G ProSe direct link, if the 5G ProSe direct link establishment procedure is used for 5G ProSe direct communication between a 5G ProSe Layer 3 Inter-UE Relay UE and a target 5G ProSe Layer 3 end UE.

[0497] NOTE 6B: The UE implementation ensures that any value of the self-assigned Source Layer 2 ID in a) and b) is different from any other self-assigned Source Layer 2 ID and different pairs of User Information ID of the source 5G ProSe-side UE and User Information ID of the target 5G ProSe-side UE in 5G ProSe direct communication for unstructured traffic, if the 5G ProSe direct link establishment procedure is used for 5G ProSe direct communication between a 5G ProSe Layer 3 Inter-UE Relay UE and a target 5G ProSe Layer 3-side UE and for unstructured traffic.

[0498] NOTE 7: The initiating UE may reuse the Layer 2 ID of the initiating UE used in the previous 5G ProSe direct link with the same peer UE, except that the 5G ProSe direct link establishment procedure is used for 5G ProSe direct communication between a 5G ProSe Layer 3 inter-UE relay UE and a target 5G ProSe Layer 3 end UE for unstructured traffic and different pairs of User Information ID of the source 5G ProSe end UE and User Information ID of the target 5G ProSe end UE, and the 5G ProSe direct link establishment procedure is used for 5G ProSe direct communication between a 5G ProSe Layer 3 inter-UE relay UE and a target 5G ProSe Layer 3 end UE with a data unit type different from that of the previous 5G ProSe direct link.

[0499] And start timer T5080.

[0500] NOTE 8: The preset PC5 DRX configuration is used to transmit the ProSe Direct Link Setup Request message, as specified in 3GPP TS 38.300

[21] .

[0501] While timer T5080 is running, the UE shall not send a new ProSe Direct Link Setup Request message to the same target UE identified by the same application layer ID. If the Target User Information IE is not included in the ProSe Direct Link Setup Request message (i.e., 5G ProSe Direct Link Setup procedure for ProSe applications), the initiating UE shall process multiple ProSe Direct Link Setup Accept messages (if any) received from different target UEs for establishing multiple 5G ProSe direct links before the expiration of timer T5080.

[0502] NOTE 9: To ensure a successful 5G ProSe direct link establishment, T5080 should be set to a value greater than the sum of T5089 and T5092.

[0503] [3GPP TS 24.554 V18.1.0 titled "5G ProSe direct link establishment procedure towards UE" Figure 7 .2.2.2.1 Reproduced as Figure 16 ]

[0504] [3GPP TS 24.554 V18.1.0 titled "5G ProSe direct link establishment procedure for ProSe services" Figure 7 .2.2.2.2 Reproduced as Figure 17 ]

[0505] 7.2.2.3 5G ProSe Direct Link Establishment Procedure Accepted by Target UE

[0506] After receiving the ProSe direct link establishment request message, if the target UE accepts the request, the target UE will uniquely assign a PC5 link identifier and create a 5G ProSe direct link context.

[0507] NOTE 1: The PC5 DRX configuration is preset for receiving the ProSe Direct Link Setup Request message as specified in 3GPP TS 38.300

[21] .

[0508] If the ProSe Direct Link Setup Request message is for 5G ProSe direct communication between a 5G ProSe remote UE and a 5G ProSe UE to a network relay UE, the target UE shall verify the MIC field in the received ProSe Direct Link Setup Request with the DUIK (if present) and decrypt the encrypted MIC using DUCK or DUSK:

[0509] a) Relay service code; and

[0510] b) UP-PRUK ID or CP-PRUK ID (if received),

[0511] The associated encrypted bit mask is used for 5G ProSe UE to network relay discovery (see section 6.3.5.2 of 3GPP TS 33.503

[34] ) and verifies whether the relay service code matches the code sent by the target UE during the 5G ProSe UE to network relay discovery procedure.

[0512] NOTE 2: If the UE is configured to use neither DUCK nor DUSK, the relay service code and UP-PRUK ID or CP-PRUK ID are not encrypted.

[0513] If the target UE acts as a target 5G ProSe end UE and the 5G ProSe direct link establishment procedure is used for direct communication with integrated discovery between a 5G ProSe inter-UE relay UE and a target 5G ProSe end UE, then upon receiving a ProSe direct link establishment request message containing the same source user information, ProSe identifier and relay service code as received from multiple 5G ProSe inter-UE relay UEs, the target UE selects one of the 5G ProSe inter-UE relay UEs to communicate with the source 5G ProSe end UE, as specified in section 6.7.3.2 of TS 23.304.

[0514] If the 5G ProSe direct link establishment procedure is not used for direct communication between a 5G ProSe remote UE and a 5G ProSe UE to a network relay UE, the target UE may initiate the 5G ProSe direct link authentication procedure specified in section 7.2.12 and shall initiate the 5G ProSe direct link security mode control procedure specified in section 7.2.10.

[0515] If the 5G ProSe direct link establishment procedure is used for direct communication between a 5G ProSe remote UE and a 5G ProSe UE to network relay UE, the target UE shall proceed with:

[0516] a) authentication and key agreement procedures as specified in section 5.5.4 of 3GPP TS 24.501

[11] , provided that the security procedures on the control plane as specified in 3GPP TS 33.503

[34] are used; or

[0517] b) the key request procedure as specified in section 8.2.10.2.4, provided that the security procedures on the user plane as specified in 3GPP TS 33.503

[34] are used;

[0518] And the 5G ProSe direct link security mode control procedure will be initiated as specified in Section 7.2.10.

[0519] In the 5G ProSe direct link context, the target UE shall set the source Layer 2 ID and destination Layer 2 ID as specified in Section 7.2.12 and Section 7.2.10, and store the corresponding source Layer 2 ID for unicast communication and store the destination Layer 2 ID for unicast communication.

[0520] if:

[0521] a) The Target User Information IE is included in the ProSe Direct Link Setup Request message, and this IE contains the application layer ID of the target UE; or

[0522] b) the target user information IE is not included in the ProSe direct link setup request message, and the target UE is interested in the ProSe application identified by the ProSe identifier IE in the ProSe direct link setup request message;

[0523] The target UE will then:

[0524] a) If the direct communication is not between a 5G ProSe remote UE and a 5G ProSe UE to a network relay UE:

[0525] 1) Based on K contained in the ProSe direct link establishment request message NRP ID, identifies the existing K NRP ;or

[0526] 2) If K NRP If the ID is not included in the ProSe direct link establishment request message, the target UE will use the K NRP ID does not have an existing K NRP , or the target UE wishes to derive a new K NRP This may require execution of one or more 5G ProSe direct link authentication procedures, as specified in Section 7.2.12;

[0527] b) If the direct communication is between a 5G ProSe Remote UE and a 5G ProSe UE to a network relay UE and the security procedures on the control plane specified in 3GPP TS 33.503

[34] are used, then a new K is requested according to the security procedures on the user plane specified in 3GPP TS 33.503

[34] . NR_ProSe ;or

[0528] c) If the direct communication is between a 5G ProSe remote UE and a 5G ProSe UE to network relay UE and the security procedures on the user plane specified in 3GPP TS 33.503

[34] are used, then a new K is requested according to the security procedures on the user plane. NRP .

[0529] Note 3: How many times do you need to perform the 5G ProSe direct link authentication procedure to derive a new K NRP Depends on the authentication method used.

[0530] In the identification of existing K NRP Or export new K NRP Afterwards, or upon receiving a new K NRP or K NR_ProSe Afterwards, the target UE shall initiate the 5G ProSe direct link security mode control procedure as specified in Section 7.2.10.

[0531] After the 5G ProSe direct link security mode control procedure is successfully completed, in order to determine whether the ProSe direct link establishment request message is acceptable, in the case of IP communication, the target UE verifies whether there is at least one common IP address configuration option supported by both the initiating UE and the target UE.

[0532] Before sending the ProSe Direct Link Setup Accept message to the 5G ProSe Remote UE, the target UE acting as a relay UE for the 5G ProSe Layer 3 UE to the network initiates the UE-Requested PDU Session Establishment procedure as specified in 3GPP TS 24.501

[11] , provided that:

[0533] 1) The PDU session for relaying the service associated with the RSC has not been established; or

[0534] 2) A PDU session for relaying services associated with the RSC has been established, but the PDU session type is unstructured.

[0535] If the target UE accepts the 5G ProSe direct link establishment procedure, the target UE will create a ProSe direct link establishment accept message.

[0536] a) contains source user information, which is set to the application layer ID of the target UE received from upper layers, or is set to the user information ID of the target 5G ProSe UE when the 5G ProSe direct link establishment procedure is used for 5G ProSe direct communication between a 5G ProSe UE and a 5G ProSe inter-UE relay UE;

[0537] aa) including the inter-UE relay UE user information, which is set to the user information ID of the 5G ProSe inter-UE relay UE when the 5G ProSe direct link establishment procedure is used for 5G ProSe direct communication between the source 5G ProSe end UE and the 5G ProSe inter-UE relay UE;

[0538] b) shall contain the PQFI, the corresponding PC5 QoS parameters and, optionally, the ProSe identifier accepted by the target UE, if the target UE does not act as a 5G ProSe Layer 2 UE-to-network relay UE and the 5G ProSe direct link establishment procedure is not integrated with discovery and is not used for 5G ProSe direct communication between the target 5G ProSe end UE and a 5G ProSe inter-UE relay UE;

[0539] c) PC5 QoS rules may be included, provided that the target UE does not act as a relay UE for a 5G ProSe Layer 2 UE to the network, and the 5G ProSe direct link establishment procedure is not integrated with discovery and is not used for 5G ProSe direct communication between the target 5G ProSe end UE and a 5G ProSe inter-UE relay UE;

[0540] Editor's Note: How to forward PC5 QoS parameters and PQFI of PC5 QoS flows between 5G ProSe Layer 3 inter-UE relay UE and 5G ProSe Layer 3 end UE is for further study.

[0541] d) If IP communication is used and the target UE does not act as a relay UE for a 5G ProSe Layer 2 UE to the network, then the IP Address Configuration IE shall be included and set to one of the following values:

[0542] 1) "DHCPv4 server", provided that only IPv4 address allocation mechanism is supported by the target UE, i.e., acting as a DHCPv4 server;

[0543] 2) “IPv6 router”, provided that only IPv6 address allocation mechanisms are supported by the target UE, i.e., acting as an IPv6 router;

[0544] 3) "DHCPv4 server and IPv6 router", provided that both IPv4 and IPv6 address allocation mechanisms are supported by the target UE; or

[0545] 4 “) Address allocation is not supported”, provided that both IPv4 and IPv6 address allocation mechanisms are not supported by the target UE and the target UE does not act as a relay UE for 5G ProSe Layer 3 UE to the network;

[0546] NOTE 4: If the communication uses Ethernet or Unstructured Data Unit Type, the UE does not include the IP Address Configuration IE nor the Link-Local IPv6 Address IE.

[0547] e) If the IP Address Configuration IE is set to "Address Allocation Not Supported", the received ProSe Direct Link Security Mode Complete message contains a Link-Local IPv6 Address IE and the target UE acts neither as a 5G ProSe Layer 2 UE to the network relay UE nor as a 5G ProSe Layer 3 relay UE, then a Link-Local IPv6 Address IE formed locally based on IETF RFC 4862

[25] shall be included;

[0548] f) shall contain the configuration of UE PC5 unicast user plane security protection based on the agreed user plane security policy, as specified in 3GPP TS 33.503

[34] ;

[0549] Editor's note: Security parameters for 5G ProSe inter-UE relaying and parameters for 5G ProSe layer 2 inter-UE relaying are for further study.

[0550] g) if the 5G ProSe Direct Link Establishment procedure is used for 5G ProSe direct communication between a source or target 5G ProSe Layer 3 UE and a 5G ProSe Layer 3 Inter-UE Relay UE and is used for Ethernet traffic, then the MAC address of the target 5G ProSe Layer 3 UE shall be included; and

[0551] h) may include the target 5G ProSe layer 3 UE IP address IE, which is set to the IP address of the target 5G ProSe layer 3 UE if the 5G ProSe direct link establishment procedure is used for 5G ProSe direct communication between the source 5G ProSe layer 3 UE and the 5G ProSe layer 3 inter-UE relay UE and the data unit type of the communication is IP.

[0552] Editor's note: Security parameters for 5G ProSe inter-UE relaying and parameters for 5G ProSe layer 2 inter-UE relaying are for further study.

[0553] After the ProSe Direct Link Setup Accept message is generated, the target UE passes this message together with the Layer 2 ID of the initiating UE for unicast communication and the Layer 2 ID of the target UE for unicast communication to the lower layer for transmission, and starts the timer T5090, if:

[0554] a) at least one ProSe identifier used for the 5G ProSe direct link meets the privacy requirements specified in Section 5.2.4; or

[0555] b) T5090 is configured as specified in Section 5.2.5.

[0556] NOTE 5: Two UEs negotiate the PC5 DRX configuration in the AS layer, and the PC5 DRX parameter value is configured according to a pair of source / destination Layer 2 IDs in the AS layer, as specified in 3GPP TS 38.300

[21] .

[0557] After sending the ProSe Direct Link Setup Accept message, the target UE provides the following information together with the Layer 2 ID to the lower layers, which enables the lower layers to process the incoming PC5 signaling or traffic data:

[0558] a) A self-assigned PC5 link identifier for this 5G ProSe direct link;

[0559] b) PQFI and its corresponding PC5 QoS parameters (if applicable); and

[0560] c) Indication to activate PC5 unicast user plane security protection for 5G ProSe direct link (if applicable).

[0561] If the target UE accepts the 5G ProSe direct link establishment request and the 5G ProSe direct link is established but is not used for 5G ProSe direct communication between a 5G ProSe remote UE and a 5G ProSe UE-to-network relay UE and is not used for 5G ProSe direct communication between a 5G ProSe end UE and a 5G ProSe inter-UE relay UE, then the target UE may perform PC5 QoS flow establishment on the 5G ProSe direct link as specified in section 7.2.7. If the 5G ProSe direct link is established for 5G ProSe layer 3 remote UE and a 5G ProSe layer 3 UE-to-network relay UE, then the target UE may perform PC5 QoS flow establishment on the 5G ProSe direct link as specified in section 8.2.6. If the 5G ProSe direct link is established for 5G ProSe direct communication between a 5G ProSe layer 3 end UE and a 5G ProSe layer 3 inter-UE relay UE, then the target UE may perform PC5 QoS flow establishment on the 5G ProSe direct link as specified in section 8a.2.7.

[0562] 7.2.2.4 5G ProSe Direct Link Establishment Procedure Completed by Initiating UE

[0563] If the Target User Information IE is included in the ProSe Direct Link Setup Request message, the initiating UE will stop timer T5080 after receiving the ProSe Direct Link Setup Accept message. If the Target User Information IE is not included in the ProSe Direct Link Setup Request message, the initiating UE may keep timer T5080 running and continue to process multiple response messages (i.e., ProSe Direct Link Setup Accept messages) from multiple target UEs.

[0564] For each ProSe Direct Link Setup Accept message received, the initiating UE will uniquely assign a PC5 link identifier and create a 5G ProSe direct link context for each 5G ProSe direct link. The initiating UE will then store the source Layer 2 ID and destination Layer 2 ID used to transmit this message provided by the lower layer in the 5G ProSe direct link context to complete the establishment of the 5G ProSe direct link with the target UE. From then on, the initiating UE will use the established link for ProSe direct communication over PC5 and additional PC5 signaling messages to the target UE.

[0565] If the initiating UE acts as a 5G ProSe inter-UE relay and the 5G ProSe direct link establishment procedure is used for direct communication with integrated discovery between the 5G ProSe inter-UE relay UE and the target 5G ProSe side UE, then after receiving the ProSe direct link setup accept message from the target 5G ProSe side UE, the initiating UE shall initiate the 5G ProSe direct link security mode control procedure with the source 5G ProSe side UE, and after successfully completing the 5G ProSe direct link security mode control procedure with the source 5G ProSe side UE, the initiating UE shall create a ProSe direct link setup accept message as specified in Section 7.2.2.3 to send to the source 5G ProSe side UE.

[0566] After receiving the ProSe Direct Link Setup Accept message, the initiating UE provides the following information together with the Layer 2 ID to the lower layers so that the lower layers can process the incoming PC5 signaling or traffic data:

[0567] a) A self-assigned PC5 link identifier for this 5G ProSe direct link;

[0568] b) PQFI and its corresponding PC5 QoS parameters (if applicable); and

[0569] c) Indication to activate PC5 unicast user plane security protection for 5G ProSe direct link (if applicable).

[0570] The initiating UE shall start timer T5090 if:

[0571] a) at least one ProSe identifier used for the 5G ProSe direct link meets the privacy requirements specified in Section 5.2.4; or

[0572] b) T5090 is configured as specified in Section 5.2.5.

[0573] Additionally, the initiating UE may perform PC5 QoS flow establishment on the 5G ProSe direct link as specified in section 7.2.7.

[0574] After timer T5080 expires, if the ProSe Direct Link Setup Request message does not include the Target User Information IE and the initiating UE receives at least one ProSe Direct Link Setup Accept message, it is up to the UE implementation whether to consider the 5G ProSe Direct Link Setup procedure as completed or restart timer T5080.

[0575] If the 5G ProSe direct link establishment procedure is triggered by a ProSe Direct Link Modify Request message from a source 5G ProSe Layer 3 end UE, as specified in section 7.2.3.2, then in the case where the initiating UE acts as a 5G ProSe Layer 3 inter-UE relay UE, upon receiving the ProSe Direct Link Setup Accept message, the initiating UE shall send a ProSe Direct Link Modify Accept message to the source 5G ProSe Layer 3 end UE, as specified in section 7.2.3.3.

[0576] 7.2.2.5 5G ProSe Direct Link Establishment Procedure Not Accepted by Target UE

[0577] If the ProSe Direct Link Setup Request message cannot be accepted, the target UE shall send a ProSe Direct Link Setup Reject message. The ProSe Direct Link Setup Reject message contains the PC5 signaling protocol cause IE, which is set to one of the following cause values:

[0578] #1 Direct communication with the target UE is not allowed;

[0579] #3 A conflict of layer 2 IDs for unicast communication is detected;

[0580] #5 Lack of resources for 5G ProSe direct links;

[0581] #13 Congestion situation;

[0582] #15 5G ProSe UE to network relay security procedure failure;

[0583] #20 Failure from 5G ProSe UE; or

[0584] #111 Unspecified protocol error.

[0585] If the target UE is not allowed to accept the ProSe Direct Link Setup Request message, e.g., based on operator policy or configuration parameters for ProSe direct communication over PC5, as specified in section 5.2, or the target UE acts as a relay UE for a 5G ProSe Layer 3 UE to the network, in a disallowed area of ​​its serving PLMN and the corresponding relay service code is not associated with high priority access, as defined in section 5.3.5 of 3GPP TS 24.501

[11] , then the target UE shall send a ProSe Direct Link Setup Reject message with PC5 signaling protocol cause value #1 "Direct communication with target UE not allowed".

[0586] NOTE 1: When a target UE acting as a relay UE of a 5G ProSe Layer 3 UE to the network is involved in its own emergency services as specified in 3GPP TS 24.501

[11] or handling emergency services of another 5G ProSe Layer 3 remote UE, and receives a ProSe Direct Link Setup Request message with an RSC specific to emergency services, the target UE is allowed to ignore the ProSe Direct Link Setup Request message if it decides to prioritize its own ongoing emergency services or handling emergency services of other 5G ProSe Layer 3 remote UE due to local regulations or implementation-specific requirements.

[0587] For a ProSe Direct Link Setup Request message received from a Layer 2 ID (for unicast communication), if the target UE already has an existing link to the UE using this Layer 2 ID or is currently processing a ProSe Direct Link Setup Request message from the same Layer 2 ID and one of the following parameters is different from the existing link or the link for which link setup is in progress:

[0588] a) Source user information;

[0589] b) the type of data (e.g. IP, Ethernet, or unstructured); or

[0590] c) Security policy,

[0591] The target UE shall send a ProSe Direct Link Setup Reject message containing the PC5 signaling protocol cause value #3 “Detection of conflict of Layer 2 ID for unicast communication”.

[0592] NOTE 2: If the UE is processing a ProSe Direct Discovery message for the same source Layer 2 ID from a received ProSe Direct Link Setup Request message, avoiding the conflict of the destination Layer 2 ID is up to the UE implementation (e.g., sending a ProSe Direct Link Setup Reject message with PC5 signaling protocol cause value #3 "Conflict of Layer 2 IDs detected for unicast communication" or ignoring the ProSe Direct Discovery message).

[0593] NOTE 3: The type of data (e.g., IP, Ethernet, or unstructured) is indicated by the optional IP Address Configuration IE included in the corresponding Direct Link Security Mode Complete message, i.e., if this IE is included, the type of data for the requested link is IP type, and if this IE is not included, the type of data for the requested link is Ethernet or unstructured.

[0594] If the 5G ProSe direct link establishment fails due to reaching the implementation-specific maximum number of established 5G ProSe direct links or other temporary lower layer issues causing resource constraints, the target UE shall send a ProSe Direct Link Setup Reject message with PC5 signaling protocol cause value #5 "Lack of resources for 5G ProSe direct link".

[0595] If the 5G ProSe direct link establishment request is for 5G ProSe UE to network relay and:

[0596] a) activating NAS-level mobility management congestion control as specified in section 5.3.9 of TS 24.501

[11] at the target UE acting as a relay UE for the 5G ProSe UE to the network; or

[0597] b) The target UE acting as a relay UE from the 5G ProSe UE to the network is under congestion;

[0598] The target UE shall send a ProSe Direct Link Setup Reject message with PC5 signaling protocol cause value #13 "Congestion Situation". The target UE may provide the back-off timer value to the initiating UE in the ProSe Direct Link Setup Reject message. If the back-off timer for NAS-level mobility management congestion control is running, the target UE shall not accept any 5G ProSe direct link setup request for relay.

[0599] If the 5G ProSe direct link setup request is for 5G ProSe UE to network relay, NAS level session management congestion as specified in sections 6.2.7 and 6.2.8 of TS 24.501

[11] is activated at the target UE acting as a 5G ProSe Layer 3 UE to network relay UE, the relay service code for the 5G ProSe direct link setup corresponds to the DNN and / or S-NSSAI in which NAS level session management congestion is activated, and the target UE needs to perform the PDU Session Establishment procedure for DNN and / or S-NSSAI or the PDU Session Modification procedure for DNN and / or S-NSSAI, then the target UE shall send a ProSe Direct Link Setup Reject message with PC5 signaling protocol cause value #13 "Congestion situation". The target UE may provide the back-off timer value to the initiating UE in the ProSe Direct Link Setup Reject message.

[0600] NOTE 4: How the target UE determines that it is under congestion is implementation specific (e.g. any relay related operation overhead, etc.).

[0601] NOTE 5: In case the target UE is under NAS level mobility management congestion control, setting the back-off timer value provided to the initiating UE to the remaining time of the mobility management back-off timer T3346 or with an additional offset value is an implementation option.

[0602] If the 5G ProSe direct link establishment request is for 5G ProSe Layer 3 UE to network relay, the request requires establishment of a PDU session for the 5G ProSe Layer 3 UE to network relay UE acting as the target UE, and the PDU session establishment is unsuccessful due to receiving 5GSM cause #8 "maximum number of PDU sessions reached", #27 "DNN missing or unknown", #28 "PDU session type unknown", #29 "User authentication or authorization failed", #31 "Unspecified reject request", #32 "Service option not supported", #33 "Requested service option not subscribed" or #65 "maximum number of PDU sessions reached", as specified in 3GPP TS 24.501

[11] , then the target UE shall send a ProSe direct link establishment reject message with PC5 signalling protocol cause value #111 "Unspecified protocol error".

[0603] If the 5G ProSe direct link establishment request is for 5G ProSe inter-UE relay, and:

[0604] a) The target UE acting as the target 5G ProSe end UE is in congestion;

[0605] The target UE shall send a ProSe direct link setup reject message with PC5 signaling protocol cause value #13 "Congestion situation". The target UE may provide the back-off timer value to the initiating UE in the ProSe direct link setup reject message.

[0606] After receiving the ProSe direct link establishment reject message from the target 5G ProSe side UE, the initiating UE acts as a 5G ProSe inter-UE relay UE, and the 5G ProSe direct link establishment procedure is used for direct communication between the source 5G ProSe side UE and the 5G ProSe inter-UE relay UE. The target 5G ProSe side UE has rejected the 5G ProSe direct link establishment procedure or the 5G ProSe direct link modification procedure. The rejection message contains a backoff value. The initiating UE has not reached the maximum number of allowed retransmissions. The initiating UE will notify (message TBD) the source 5G ProSe side UE that the target 5G ProSe side UE has rejected the link establishment or link modification request, and will provide the cause value from the target 5G ProSe side UE.

[0607] Editor's note: How the target 5G ProSe UE notifies the 5G ProSe inter-UE relay UE of its rejection of the link establishment or link modification request is for further study.

[0608] After receiving a ProSe Direct Link Setup Reject message from a target 5G ProSe side UE, the initiating UE acts as a 5G ProSe inter-UE relay UE, the 5G ProSe Direct Link Setup procedure is used for direct communication between the source 5G ProSe side UE and the 5G ProSe inter-UE relay UE, the target 5G ProSe side UE has rejected the 5G ProSe Direct Link Setup procedure or the 5G ProSe Direct Link Modification procedure, the Reject message contains a Backoff value, and the initiating UE has reached the maximum number of allowed retransmissions, the initiating UE may send a ProSe Direct Link Setup Reject message with an appropriate PC5 signaling protocol cause value to the source 5G ProSe side UE. The initiating UE shall include the PC5 protocol cause value #xx "Failure from 5G ProSe side UE" in the ProSe Direct Link Setup Reject message, and the PC5 UE Failure Cause IE set to #13 "Congestion Condition" received from the target 5G ProSe side UE that rejected the 5G ProSe Direct Link Setup or 5G ProSe Direct Link Modification procedure. The initiating UE may include the target UE information IE set to the user information ID of the target 5G ProSe UE in the ProSe direct link establishment rejection message.

[0609] If the 5G ProSe direct link establishment request is for 5G ProSe inter-UE relay, and:

[0610] a) The target UE acting as a 5G ProSe inter-UE relay UE is in congestion;

[0611] The target UE shall send a ProSe direct link setup reject message with PC5 signaling protocol cause value #13 "Congestion situation". The target UE may provide the back-off timer value to the initiating UE in the ProSe direct link setup reject message.

[0612] If the 5G ProSe direct link establishment procedure is used for direct communication between a 5G ProSe remote UE and a 5G ProSe UE to network relay UE and fails due to a failure of the security procedure on the control plane or the security procedure on the user plane as specified in 3GPP TS 33.503

[34] , the target UE shall send a ProSe direct link establishment reject message with the PC5 signaling protocol cause value #15 "5G ProSe UE to network relay security procedure failure". The target UE shall provide an EAP message (if received from the network) according to the security procedure on the control plane as specified in 3GPP TS 33.503

[34] .

[0613] If the target UE acts as a target 5G ProSe end UE and the 5G ProSe direct link establishment procedure is between a 5G ProSe inter-UE relay UE and the target 5G ProSe end UE, the target 5G ProSe end UE may include the following in the ProSe direct link establishment reject message:

[0614] a) Source UE Information IE set to the user information ID of the source 5G ProSe UE;

[0615] b) Target UE Information IE set to the user information ID of the target 5G ProSe UE; and

[0616] c) Inter-UE relay UE information IE set to the user information ID of the 5G ProSe inter-UE relay UE.

[0617] If the target UE acts as a 5G ProSe inter-UE relay UE, the 5G ProSe direct link establishment procedure is between the source 5G ProSe side UE and the 5G ProSe inter-UE relay UE, and the target 5G ProSe side UE has rejected the 5G ProSe direct link establishment procedure or the 5G ProSe direct link modification procedure, then the 5G ProSe inter-UE relay UE shall send a ProSe direct link establishment reject message with a PC5 signaling protocol cause value #20 "Failure from 5G ProSe side UE" to the source 5G ProSe side UE. The 5G ProSe inter-UE relay UE may include the PC5 side UE failure cause IE in the ProSe direct link establishment reject message, which is set to the PC5 signaling protocol cause received from the target 5G ProSe side UE that rejected the 5G ProSe direct link establishment procedure. The 5G ProSe inter-UE relay UE may include the following in the ProSe direct link establishment reject message:

[0618] a) Source UE Information IE set to the user information ID of the source 5G ProSe UE;

[0619] b) Target UE Information IE set to the user information ID of the target 5G ProSe UE; and

[0620] c) Inter-UE relay UE information IE set to the user information ID of the 5G ProSe inter-UE relay UE.

[0621] NOTE 6: Cause value #15 “5G ProSe UE to Network Relay Security Procedure Failure” is also used when no CP-PRUK or UP-PRUK is found in the network.

[0622] If the 5G ProSe direct link establishment fails for other reasons, the target UE shall send a ProSe direct link establishment reject message containing the PC5 signaling protocol cause value #111 “Unspecified protocol error”.

[0623] After sending the ProSe Direct Link Setup Reject message, the target UE shall provide the following information to the lower layer along with the Layer 2 ID of the initiating UE for unicast communication and the Layer 2 ID of the target UE for unicast communication:

[0624] a) Indication of deactivation of PC5 unicast security protection and deletion of security context for 5G ProSe direct link (if applicable).

[0625] Upon receiving the ProSe Direct Link Setup Reject message, the initiating UE will stop timer T5080 and abort the 5G ProSe direct link establishment procedure. If the PC5 signaling protocol cause value in the ProSe Direct Link Setup Reject message is #1 "Direct communication with target UE not allowed" or #5 "Lack of resources for 5G ProSe direct link", the initiating UE will not attempt to initiate a 5G ProSe direct link establishment procedure with the same target UE for at least a time period T. If the PC5 signaling protocol cause value in the ProSe Direct Link Setup Reject message is #13 "Congestion situation" and a back-off timer value is provided in the ProSe Direct Link Setup Reject message, the initiating UE will start timer T5088 associated with the Layer 2 ID of the target UE and set its value to the provided timer value. If the PC5 signaling protocol cause value in the ProSe Direct Link Setup Reject message is #15 "5G ProSe UE to Network Relay Security Procedure Failure" and the initiating UE has included the UE Identity IE set to SUCI in the ProSe Direct Link Setup Request message, then the initiating UE shall initiate the UE to Network Relay reselection procedure as specified in section 8.2.3. If the PC5 signaling protocol cause value in the ProSe Direct Link Setup Reject message is #15 "5G ProSe UE to Network Relay Security Procedure Failure" and the initiating UE has included the User Security Key ID IE set to UP-PRUK ID or CP-PRUK ID in the ProSe Direct Link Setup Request message, then the initiating UE may initiate the UE to Network Relay reselection procedure as specified in section 8.2.3 and the UE shall further:

[0626] a) if the same 5G ProSe UE is selected as a relay UE to the network, then discard the previously used CP-PRUK and associated CP-PRUK ID, or UP-PRUK and associated UP-PRUK ID (if present), and include the UE Identity IE set to SUCI in the ProSe Direct Link Establishment Request when initiating a subsequent 5G ProSe Direct Link Establishment procedure, as specified in section 7.2.2.2; or

[0627] b) If a different 5G ProSe UE is selected as a relay UE to the network, the User Security Key ID IE set to the previously used UP-PRUK ID or CP-PRUK ID is included in the ProSe Direct Link Setup Request message.

[0628] NOTE 7: The length of the time period T is UE implementation specific and may be different in the case when the UE receives PC5 signaling protocol cause value #1 "Direct communication with target UE not allowed" or in the case when the UE receives PC5 signaling protocol cause value #5 "Lack of resources for 5G ProSe direct link".

[0629] Editor's note: Security related content is for further study and depends on SA3 requirements.

[0630] After receiving the ProSe Direct Link Setup Reject message, the initiating UE shall provide the following information to the lower layer along with the Layer 2 ID of the initiating UE for unicast communication and the Layer 2 ID of the target UE for unicast communication:

[0631] a) Indication of deactivation of PC5 unicast security protection and deletion of security context for 5G ProSe direct link (if applicable).

[0632] 7.2.2.6 Abnormal situations

[0633] 7.2.2.6.1 Abnormal situation at the initiating UE

[0634] If timer T5080 expires and the Target User Information IE is included in the ProSe Direct Link Setup Request message, the initiating UE shall retransmit the ProSe Direct Link Setup Request message and restart timer T5080. After the maximum number of allowed retransmissions is reached, the initiating UE shall abort the 5G ProSe Direct Link Setup procedure and may notify upper layers that the target UE is unreachable.

[0635] After timer T5080 expires, if the ProSe direct link setup request message does not include the target user information IE and the initiating UE does not receive any ProSe direct link setup accept message, the initiating UE may retransmit the ProSe direct link setup request message and restart timer T5080. If the ProSe direct link setup request message does not include the target user information IE and the initiating UE does not receive any ProSe direct link setup accept message, the initiating UE shall abort the 5G ProSe direct link setup procedure after the maximum number of allowed retransmissions is reached and may notify upper layers that the target UE is unavailable.

[0636] NOTE: The maximum number of allowed retransmissions is UE implementation specific.

[0637] If the link establishment is no longer required before the procedure is completed, the initiating UE shall abort the procedure.

[0638] When the initiating UE aborts the 5G ProSe direct link establishment procedure, the initiating UE shall provide the following information to the lower layers along with the Layer 2 ID of the initiating UE for unicast communication and the Layer 2 ID of the target UE for unicast communication:

[0639] a) Indication of deactivation of PC5 unicast security protection and deletion of security context for 5G ProSe direct link (if applicable).

[0640] 7.2.2.6.2 Abnormal Situation at Target UE

[0641] For a ProSe Direct Link Setup Request message (for unicast communication) received from a Source Layer 2 ID, if the target UE already has an existing link established to a known UE using the same Source Layer 2 ID, the same source user information, the same data type (IP, Ethernet, or Unstructured), and the same security policy, then the UE shall process the new request. However, the target UE shall only delete the existing 5G ProSe Direct Link context after the new link establishment procedure is successful.

[0642] NOTE: The type of data (e.g., IP, Ethernet, or unstructured) is indicated by the optional IP address configuration included in the corresponding ProSe Direct Link Security Mode Complete message, i.e., if this IE is included, the type of data for the requested link is IP type, and if this IE is not included, the type of data for the requested link is Ethernet or unstructured.

[0643] If the ProSe Direct Link Setup Request message is used for 5G ProSe direct communication between a 5G ProSe remote UE and a 5G ProSe UE-to-network relay UE, then after the target UE decrypts the encrypted relay service code using DUIK, DUSK, or DUCK (where the associated encrypted bit mask is used for 5G ProSe UE-to-network relay discovery), if the relay service code does not match the relay service code sent by the target UE during the 5G ProSe UE-to-network relay discovery procedure, then the target UE shall abort the 5G ProSe direct link establishment procedure.

[0644] If the ProSe Direct Link Setup Request message is used for 5G ProSe direct communication between a 5G ProSe remote UE and a 5G ProSe UE to a network relay UE, the message integrity is protected, and the integrity verification of the message fails at the target UE, then the target UE shall abort the 5G ProSe direct link establishment procedure.

[0645] 7.2.3 5G ProSe Direct Link Modification Procedure

[0646] 7.2.3.1 Overview

[0647] The purpose of the 5G ProSe Direct Link Modification procedure is to modify the existing ProSe Direct Link to:

[0648] a) Adding new PC5 QoS flows to existing 5G ProSe direct links;

[0649] b) modifying an existing PC5 QoS flow to update the PC5 QoS parameters of the existing PC5 QoS flow;

[0650] c) Modify the existing PC5 QoS flow to associate the new ProSe application with the existing PC5 QoS flow;

[0651] d) modifying an existing PC5 QoS flow to remove the associated ProSe application from the existing PC5 QoS flow;

[0652] e) Remove existing PC5 QoS flows from existing 5G ProSe direct links;

[0653] f) Negotiate a new 5G ProSe inter-UE relay UE on the existing 5G ProSe direct link;

[0654] g) establishing 5G ProSe inter-UE relay communication with an additional 5G ProSe layer 3 end UE using an existing 5G ProSe direct link between the 5G ProSe layer 3 end UE and the 5G ProSe layer 3 inter-UE relay UE; or

[0655] h) releasing the 5G ProSe inter-UE relay communication with one of the peer 5G ProSe layer 3 end UEs using a shared 5G ProSe direct link between the 5G ProSe layer 3 end UE and the 5G ProSe layer 3 inter-UE relay UE.

[0656] In this procedure, the UE that sends the ProSe direct link modification request message is called the "initiating UE", and the other UE is called the "target UE".

[0657] Note: The 5G ProSe direct link modification procedure is not applicable to the 5G ProSe layer 2 UE to network relay case.

[0658] 7.2.3.2 5G ProSe Direct Link Modification Procedure Initiated by the Initiating UE

[0659] Before initiating this procedure to add a new ProSe application to an existing 5G ProSe direct link, the initiating UE shall meet the following prerequisites:

[0660] a) There is a 5G ProSe direct link between the initiating UE and the target UE;

[0661] b) the pair of application layer ID and network layer protocol of this 5G ProSe direct link are the same as those required by the application layer in the initiating UE of this ProSe application;

[0662] c) The security policy corresponding to the ProSe identifier is consistent with the security policy of the existing 5G ProSe direct link;

[0663] d) Timer T5091 is not running; and

[0664] e) The initiating UE does not perform the 5G ProSe direct link key update procedure initiated by the target UE.

[0665] The initiating UE shall meet the following prerequisites before initiating this procedure for negotiating a new 5G ProSe inter-UE relay UE on an existing 5G ProSe direct link:

[0666] a) The initiating UE is a source 5G ProSe UE that communicates with a target 5G ProSe UE via a 5G ProSe inter-UE relay UE;

[0667] b) The initiating UE determines to perform inter-UE relay reselection, for example based on PC5 signal strength; and

[0668] c) The initiating UE obtains a list of candidate inter-UE relays via the inter-UE discovery procedure.

[0669] After receiving service data or request from upper layers, the initiating UE shall perform PC5 QoS flow matching as specified in Section 7.2.8. If no matching PC5 QoS flow exists, the initiating UE shall derive PC5 QoS parameters and assign a PQFI for the PC5 QoS flow to be established as specified in Section 7.2.7.

[0670] If the 5G ProSe direct link modification procedure is to add a new PC5 QoS flow to an existing 5G ProSe direct link, the initiating UE shall create a ProSe Direct Link Modification Request message. In this message, the initiating UE:

[0671] a) shall contain PQFI, corresponding PC5 QoS parameters and optional ProSe identifier;

[0672] b) shall contain a link modification operation code set to “add a new PC5 QoS flow to an existing 5G ProSe direct link”;

[0673] c) a packet filter that may contain PC5 QoS rules to indicate PC5 QoS flows;

[0674] d) including the source UE information set to the user information ID of the source 5G ProSe layer 3 end UE, if the UE acts as a 5G ProSe layer 3 inter-UE relay UE, the 5G ProSe direct link is between the 5G ProSe layer 3 inter-UE relay UE and the target 5G ProSe layer 3 end UE, and multiple source 5G ProSe layer 3 end UEs establish direct communication with the target 5G ProSe layer 3 end UE via the 5G ProSe layer 3 inter-UE relay UE using the same 5G ProSe direct link;

[0675] e) may include source UE information set to the user information ID of the source 5G ProSe UE, if the UE acts as a 5G ProSe inter-UE relay UE, the 5G ProSe direct link is between the 5G ProSe inter-UE relay UE and the target 5G ProSe UE, and only one source 5G ProSe UE establishes direct communication with the target 5G ProSe UE via the 5G ProSe inter-UE relay UE using the 5G ProSe direct link;

[0676] f) including the target UE information set as the user information ID of the target 5G ProSe layer 3 UE, if the UE acts as a source 5G ProSe layer 3 UE, the 5G ProSe direct link is between the source 5G ProSe layer 3 UE and a 5G ProSe layer 3 inter-UE relay UE, and the source 5G ProSe layer 3 UE has established direct communications with multiple target 5G ProSe layer 3 UEs via the 5G ProSe layer 3 inter-UE relay UE using the same 5G ProSe direct link;

[0677] g) The target UE information may be set to the user information ID of the target 5G ProSe UE, provided that:

[0678] 1) The UE acts as a source 5G ProSe UE, the 5G ProSe direct link is between the source 5G ProSe UE and a 5G ProSe inter-UE relay UE, and the source 5G ProSe UE establishes direct communication with only one target 5G ProSe UE via the 5G ProSe inter-UE relay UE using the 5G ProSe direct link; or

[0679] 2) The UE acts as a 5G ProSe inter-UE relay UE, and the 5G ProSe direct link is between the 5G ProSe inter-UE relay UE and the target 5G ProSe end UE; and

[0680] h) may contain the target UE Layer 2 ID set to the Layer 2 ID of the target 5G ProSe UE if the UE acts as a source 5G ProSe UE and the 5G ProSe direct link is between the source 5G ProSe UE and a 5G ProSe inter-UE relay UE.

[0681] If the 5G ProSe direct link modification procedure is to modify the PC5 QoS parameters for an existing PC5 QoS flow in an existing 5G ProSe direct link, the initiating UE shall create a ProSe Direct Link Modification Request message. In this message, the initiating UE:

[0682] a) It will contain PQFI and corresponding PC5 QoS parameters, including ProSe identifier;

[0683] b) shall contain a link modification operation code set to "Modify PC5 QoS parameters of an existing PC5 QoS flow";

[0684] c) a packet filter that may contain PC5 QoS rules to indicate PC5 QoS flows;

[0685] d) including the source UE information set to the user information ID of the source 5G ProSe layer 3 end UE, if the UE acts as a 5G ProSe layer 3 inter-UE relay UE, the 5G ProSe direct link is between the 5G ProSe layer 3 inter-UE relay UE and the target 5G ProSe layer 3 end UE, and multiple source 5G ProSe layer 3 end UEs establish direct communication with the target 5G ProSe layer 3 end UE via the 5G ProSe layer 3 inter-UE relay UE using the same 5G ProSe direct link;

[0686] e) may include source UE information set to the user information ID of the source 5G ProSe UE, if the UE acts as a 5G ProSe inter-UE relay UE, the 5G ProSe direct link is between the 5G ProSe inter-UE relay UE and the target 5G ProSe UE, and only one source 5G ProSe UE establishes direct communication with the target 5G ProSe UE via the 5G ProSe inter-UE relay UE using the 5G ProSe direct link;

[0687] f) including the target UE information set as the user information ID of the target 5G ProSe layer 3 UE, if the UE acts as a source 5G ProSe layer 3 UE, the 5G ProSe direct link is between the source 5G ProSe layer 3 UE and a 5G ProSe layer 3 inter-UE relay UE, and the source 5G ProSe layer 3 UE has established direct communications with multiple target 5G ProSe layer 3 UEs via the 5G ProSe layer 3 inter-UE relay UE using the same 5G ProSe direct link;

[0688] g) The target UE information may be set to the user information ID of the target 5G ProSe UE, provided that:

[0689] 1) The UE acts as a source 5G ProSe UE, the 5G ProSe direct link is between the source 5G ProSe UE and a 5G ProSe inter-UE relay UE, and the source 5G ProSe UE establishes direct communication with only one target 5G ProSe UE via the 5G ProSe inter-UE relay UE using the 5G ProSe direct link; or

[0690] 2) The UE acts as a 5G ProSe inter-UE relay UE, and the 5G ProSe direct link is between the 5G ProSe inter-UE relay UE and the target 5G ProSe end UE; and

[0691] h) may contain the target UE Layer 2 ID set to the destination Layer 2 ID of the target 5G ProSe UE if the UE acts as a source 5G ProSe UE and the 5G ProSe direct link is between the source 5G ProSe UE and a 5G ProSe inter-UE relay UE.

[0692] If the 5G ProSe direct link modification procedure is to associate a new ProSe application with an existing PC5 QoS flow, the initiating UE shall create a ProSe direct link modification request message. In this message, the initiating UE:

[0693] a) It will contain PQFI and corresponding PC5 QoS parameters, including ProSe identifier;

[0694] b) shall contain a link modification operation code set to “associate a new ProSe application with an existing PC5 QoS flow”;

[0695] c) a packet filter that may contain PC5 QoS rules to indicate PC5 QoS flows;

[0696] d) including the source UE information set to the user information ID of the source 5G ProSe layer 3 end UE, if the UE acts as a 5G ProSe layer 3 inter-UE relay UE, the 5G ProSe direct link is between the 5G ProSe layer 3 inter-UE relay UE and the target 5G ProSe layer 3 end UE, and multiple source 5G ProSe layer 3 end UEs establish direct communication with the target 5G ProSe layer 3 end UE via the 5G ProSe layer 3 inter-UE relay UE using the same 5G ProSe direct link;

[0697] e) may include source UE information set to the user information ID of the source 5G ProSe UE, if the UE acts as a 5G ProSe inter-UE relay UE, the 5G ProSe direct link is between the 5G ProSe inter-UE relay UE and the target 5G ProSe UE, and only one source 5G ProSe UE establishes direct communication with the target 5G ProSe UE via the 5G ProSe inter-UE relay UE using the 5G ProSe direct link;

[0698] f) including the target UE information set as the user information ID of the target 5G ProSe layer 3 UE, if the UE acts as a source 5G ProSe layer 3 UE, the 5G ProSe direct link is between the source 5G ProSe layer 3 UE and a 5G ProSe layer 3 inter-UE relay UE, and the source 5G ProSe layer 3 UE has established direct communications with multiple target 5G ProSe layer 3 UEs via the 5G ProSe layer 3 inter-UE relay UE using the same 5G ProSe direct link;

[0699] g) The target UE information may be set to the user information ID of the target 5G ProSe UE, provided that:

[0700] 1) The UE acts as a source 5G ProSe UE, the 5G ProSe direct link is between the source 5G ProSe UE and a 5G ProSe inter-UE relay UE, and the source 5G ProSe UE establishes direct communication with only one target 5G ProSe UE via the 5G ProSe inter-UE relay UE using the 5G ProSe direct link; or

[0701] 2) The UE acts as a 5G ProSe inter-UE relay UE, and the 5G ProSe direct link is between the 5G ProSe inter-UE relay UE and the target 5G ProSe end UE; and

[0702] h) may contain the target UE Layer 2 ID set to the Layer 2 ID of the target 5G ProSe UE if the UE acts as a source 5G ProSe UE and the 5G ProSe direct link is between the source 5G ProSe UE and a 5G ProSe inter-UE relay UE.

[0703] If the PC5 5G ProSe Direct Link Modification procedure is to remove the associated ProSe application from an existing PC5 QoS flow, the initiating UE shall create a ProSe Direct Link Modification Request message. In this message, the initiating UE:

[0704] a) will contain the PQFI and corresponding PC5 QoS parameters, including the ProSe identifier; and

[0705] b) shall contain a link modification operation code set to “remove ProSe application from existing PC5 QoS flow”.

[0706] If the direct link modification procedure is to remove any PC5 QoS flows from an existing 5G ProSe direct link, the initiating UE shall create a ProSe Direct Link Modification Request message. In this message, the initiating UE:

[0707] a) will include the PQFI; and

[0708] b) shall contain a link modification operation code set to “remove the existing PC5 QoS flow from the existing 5G ProSe direct link”.

[0709] If the 5G ProSe direct link modification procedure is to use the existing 5G ProSe direct link between the 5G ProSe layer 3 end UE and the 5G ProSe layer 3 inter-UE relay UE to establish a 5G ProSe inter-UE relay communication with an additional 5G ProSe layer 3 end UE, the initiating UE shall create a ProSe direct link modification request message. In this message, the initiating UE:

[0710] a) contains the source UE information set to the source user information ID of the 5G ProSe layer 3 end UE received in the ProSe direct link setup request message, if the UE acts as a 5G ProSe layer 3 inter-UE relay UE and the 5G ProSe direct link is between the 5G ProSe layer 3 inter-UE relay UE and the target 5G ProSe layer 3 end UE;

[0711] b) For Ethernet traffic, the MAC address of the source 5G ProSe Layer 3 end UE shall be included if the UE acts as a 5G ProSe Layer 3 inter-UE relay UE and the 5G ProSe direct link is between the 5G ProSe Layer 3 inter-UE relay UE and the target 5G ProSe Layer 3 end UE;

[0712] c) including the target UE information set to the user information ID of the additional target 5G ProSe layer 3 UE to which the 5G ProSe inter-UE relay communication is requested, if the UE acts as a source 5G ProSe layer 3 UE and the 5G ProSe direct link is between the source 5G ProSe layer 3 UE and the 5G ProSe layer 3 inter-UE relay UE;

[0713] d) setting the ProSe identifier received from upper layers if the UE acts as a source 5G ProSe Layer 3 end UE or to the ProSe identifier received in the ProSe Direct Link Setup Request message if the UE acts as a 5G ProSe Layer 3 inter-UE relay UE;

[0714] Editor's note: Whether to include the PQFI and the corresponding PC5 QoS parameters including the ProSe identifier instead of just the ProSe identifier is for further study.

[0715] Editor's note: Whether to include and how to set the ProSe identifier for the 5G ProSe direct link between the source 5G ProSe layer 3 end UE and the 5G ProSe layer 3 inter-UE relay UE and the 5G ProSe direct link between the 5G ProSe layer 3 inter-UE relay UE and the target 5G ProSe layer 3 end UE is for further study.

[0716] e) will contain a link modification operation code set to “add a new 5G ProSe layer 3 end UE to an existing 5G ProSe direct link”; and

[0717] f) may contain the target UE Layer 2 ID set to the Layer 2 ID of the target 5G ProSe Layer 3 UE, if the UE acts as a source 5G ProSe Layer 3 UE and the 5G ProSe direct link is between the source 5G ProSe Layer 3 UE and a 5G ProSe Layer 3 inter-UE relay UE.

[0718] If the 5G ProSe Direct Link Modification procedure is to release the 5G ProSe Inter-UE Relay communication with one of the peer 5G ProSe Layer 3 End UEs using a shared 5G ProSe Direct Link between the 5G ProSe Layer 3 End UE and the 5G ProSe Layer 3 Inter-UE Relay UE, the initiating UE shall create a ProSe Direct Link Modification Request message. In this message, the initiating UE:

[0719] a) contains the source UE information set to the source user information ID of the 5G ProSe layer 3 end UE received in the ProSe direct link release request message, if the UE acts as a 5G ProSe layer 3 inter-UE relay UE and the 5G ProSe direct link is between the 5G ProSe layer 3 inter-UE relay UE and the 5G ProSe layer 3 end UE;

[0720] b) the target UE information including the user information ID of the peer 5G ProSe Layer 3 UE with which the 5G ProSe inter-UE relay communication is to be released, if the UE acts as a 5G ProSe Layer 3 UE and the 5G ProSe direct link is between the 5G ProSe Layer 3 UE and the 5G ProSe Layer 3 inter-UE relay UE; and

[0721] c) shall contain a link modification operation code set to "remove 5G ProSe layer 3 end UE from the existing 5G ProSe direct link".

[0722] If the 5G ProSe direct link modification procedure is to trigger inter-UE relay reselection, the initiating UE shall create a ProSe direct link modification request message. In this message:

[0723] 1) If the initiating UE acts as the source 5G ProSe end UE, and the 5G ProSe direct link is between the source 5G ProSe end UE and the 5G ProSe inter-UE relay UE, then the initiating UE:

[0724] a) will contain a relay reselection indication;

[0725] b) A list containing candidate 5G ProSe inter-UE relay UE user information IDs;

[0726] c) a list containing the target 5G ProSe UE IP addresses / prefixes, if IP communication is used; and

[0727] d) May include a list of candidate 5G ProSe Inter-UE Relay UE Layer 2 IDs.

[0728] 2) If the initiating UE acts as a 5G ProSe inter-UE relay UE, and the 5G ProSe direct link is between the 5G ProSe inter-UE relay UE and the target 5G ProSe end UE, then the initiating UE:

[0729] a) will contain a relay reselection indication;

[0730] b) A list containing candidate 5G ProSe inter-UE relay UE user information IDs;

[0731] c) will contain the originating 5G ProSe UE IP address / prefix, if IP communication is used; and

[0732] d) May include a list of candidate 5G ProSe Inter-UE Relay UE Layer 2 IDs.

[0733] Editor's Note: The ProSe Direct Link Modification Request message needs to be updated.

[0734] If the 5G ProSe direct link modification procedure is to trigger relay reselection and the initiating UE acts as a 5G ProSe inter-UE relay UE, the initiating UE shall create a ProSe direct link modification request message for each IP address / prefix of the target 5G ProSe UE received from the 5G ProSe source UE on the associated ProSe direct link modification request message.

[0735] After the ProSe Direct Link Modification Request message is generated, the initiating UE passes this message along with the Layer 2 ID of the initiating UE for 5G ProSe direct communication and the Layer 2 ID of the target UE for 5G ProSe direct communication to lower layers for transmission, and starts timer T5081. While timer T5081 is running, the UE shall not send a new ProSe Direct Link Modification Request message to the same target UE.

[0736] [3GPP TS 24.554 V18.1.0 titled “5G ProSe Direct Link Modification Procedure” Figure 7 .2.3.2.1 Reproduced as Figure 18 ]

[0737] [3GPP TS 24.554 V18.1.0 titled “5G ProSe Direct Link Modification Procedure for Layer 3 Inter-UE Reselection” Figure 7 .2.3.2.2 Reproduced as Figure 19 ]

[0738] 7.2.3.3 5G ProSe Direct Link Modification Procedure Accepted by Target UE

[0739] If the ProSe direct link modification request message is accepted, the target UE will respond with a ProSe direct link modification accept message.

[0740] If the ProSe direct link modification request message is to add a new ProSe application, add a new PC5 QoS flow, or modify any existing PC5 QoS flow in the 5G ProSe direct link, the target UE:

[0741] a) shall contain the PQFI, the corresponding PC5 QoS parameters and, optionally, the ProSe identifier accepted by the target UE;

[0742] b) PC5 QoS rules that may include packet filters for indicating PC5 QoS flows;

[0743] c) including the source UE information set to the user information ID of the source 5G ProSe layer 3 UE, if the UE acts as a target 5G ProSe layer 3 UE, the 5G ProSe direct link is between the 5G ProSe layer 3 inter-UE relay UE and the target 5G ProSe layer 3 UE, and the target 5G ProSe layer 3 UE has established direct communications with multiple source 5G ProSe layer 3 UEs using the same 5G ProSe direct link by the 5G ProSe layer 3 inter-UE relay UE; and

[0744] d) may include source UE information set to the user information ID of the source 5G ProSe end UE, if the UE acts as a target 5G ProSe end UE, the 5G ProSe direct link is between the 5G ProSe inter-UE relay UE and the target 5G ProSe end UE, and the target 5G ProSe end UE has established direct communication with only one source 5G ProSe end UE using the 5G ProSe direct link by the 5G ProSe inter-UE relay UE; and

[0745] e) including the target UE information set as the user information ID of the target 5G ProSe UE, if the UE acts as a 5G ProSe inter-UE relay UE, the 5G ProSe direct link is between the source 5G ProSe UE and the 5G ProSe inter-UE relay UE, and the source 5G ProSe layer 3 UE has established direct communications with multiple target 5G ProSe layer 3 UEs using the same 5G ProSe direct link by the 5G ProSe layer 3 inter-UE relay UE;

[0746] f) target UE information which may include the user information ID of the target 5G ProSe UE, if the UE acts as a 5G ProSe inter-UE relay UE, the 5G ProSe direct link is between the source 5G ProSe UE and the 5G ProSe inter-UE relay UE, and the source 5G ProSe UE has established direct communication with only one target 5G ProSe UE using the 5G ProSe direct link by the 5G ProSe inter-UE relay UE;

[0747] In the ProSe Direct Link Modification Accept message.

[0748] If the ProSe direct link modification request message is to remove an existing ProSe application from the 5G ProSe direct link, the target UE will delete the ProSe identifier received in the ProSe direct link modification request message and the corresponding PQFI and PC5 QoS parameters from the attribute set associated with the 5G ProSe direct link.

[0749] If the ProSe direct link modification request message is to remove an existing PC5 QoS flow from the PC5 5G ProSe direct link, the target UE will delete the PQFI and corresponding PC5 QoS parameters from the attribute set associated with the 5G ProSe direct link.

[0750] If the ProSe direct link modification request message is to add a new ProSe application, add a new PC5 QoS flow, or modify any existing PC5 QoS flow in the 5G ProSe direct link, then after sending the ProSe direct link modification accept message, the target UE provides the added or modified PQFI and corresponding PC5 QoS parameters and PC5 link identifier to the lower layer.

[0751] If the ProSe direct link modification request message is to remove an existing ProSe application or to remove an existing PC5 QoS flow from the 5G ProSe direct link, then after sending the ProSe direct link modification accept message, the target UE provides the removed PQFI and PC5 link identifier to the lower layer.

[0752] If the ProSe direct link modification request message is to establish 5G ProSe inter-UE relay communication with an additional 5G ProSe layer 3 end UE using an existing 5G ProSe direct link between the 5G ProSe layer 3 end UE and the 5G ProSe layer 3 inter-UE relay UE, the target UE:

[0753] a) if acting as a 5G ProSe Layer 3 Inter-UE Relay UE, shall perform the 5G ProSe Direct Link Establishment procedure towards the target 5G ProSe Layer 3 end UE as specified in Section 7.2.2.2; and shall create a ProSe Direct Link Modification Accept message after receiving a ProSe Direct Link Establishment Accept message from the target 5G ProSe Layer 3 end UE;

[0754] b) If acting as the target 5G ProSe Layer 3 end UE, a ProSe Direct Link Modification Accept message will be created; and

[0755] c) In the ProSe Direct Link Modification Accept message, the target UE:

[0756] 1) If the UE acts as a target 5G ProSe Layer 3 UE, the source UE information shall be set to the user information ID of the source 5G ProSe Layer 3 UE; or

[0757] 2) If the UE acts as a 5G ProSe layer 3 inter-UE relay UE:

[0758] i) The target UE information including the user information ID of the target 5G ProSe layer 3 UE is set;

[0759] ii) For IP services, a target 5G ProSe Layer 3 UE IP address IE may be included, which is set to the IP address of the additional target 5G ProSe Layer 3 UE; and

[0760] iii) For Ethernet services, it will include the MAC address of the target 5G ProSe layer 3 end UE.

[0761] If the ProSe Direct Link Modification Request message is to release 5G ProSe inter-UE relay communication with one of the peer 5G ProSe Layer 3 end UEs using a shared 5G ProSe direct link between the 5G ProSe Layer 3 end UE and a 5G ProSe Layer 3 inter-UE relay UE, the target UE:

[0762] a) If acting as a 5G ProSe Layer 3 inter-UE relay UE, one of the following procedures may be initiated towards the target 5G ProSe Layer 3 end UE:

[0763] 1) 5G ProSe Direct Link Release procedure, as specified in Section 7.2.6.2, for releasing the 5G ProSe Direct Link with a peer 5G ProSe Layer 3 UE; or

[0764] 2) 5G ProSe Direct Link Modification procedure, as specified in Section 7.2.3.2, for removing the corresponding PC5 QoS flow if the UE determines to maintain the 5G ProSe direct link with the peer 5G ProSe Layer 3 UE; and

[0765] b) A ProSe Direct Link Modification Accept message will be created, and in this message, the target UE:

[0766] 1) The source UE information will be included as the user information ID of the source 5G ProSe Layer 3 UE, if the UE acts as a target 5G ProSe Layer 3 UE; or

[0767] 2) The target UE information shall be included as the user information ID of the target 5G ProSe layer 3 UE if the UE acts as a 5G ProSe layer 3 inter-UE relay UE.

[0768] If the 5G ProSe direct link is used for 5G ProSe direct communication between a 5G ProSe remote UE and a 5G ProSe layer 3 UE-to-network relay UE, and if the initiating UE is a 5G ProSe remote UE, the target UE (as a 5G ProSe layer 3 UE-to-network relay UE) performs the QoS flow handling procedures as specified in sections 8.2.6.3.3 and 8.2.6.4.2.

[0769] If the ProSe direct link modification request message is for inter-UE relay UE reselection, the target UE may perform a 5G ProSe inter-UE relay discovery procedure with the user information ID of the candidate 5G ProSe inter-UE relay in the discovery message, and may set the layer 2 ID of the candidate 5G ProSe inter-UE relay as the destination layer 2 ID to carry the discovery message, if received in the ProSe direct link modification request message.

[0770] If the ProSe direct link modification request message is accepted to trigger inter-UE relay reselection, the target UE will establish a PC5 unicast link with the selected 5G ProSe inter-UE relay UE (if such a PC5 unicast link does not already exist), and the 5G ProSe direct link is between the target 5G ProSe end UE and the 5G ProSe inter-UE relay UE.

[0771] If the ProSe Direct Link Modification Request message is accepted to trigger relay reselection, the target UE shall respond with a ProSe Direct Link Modification Accept message. In this message:

[0772] 1) If the target UE acts as a target 5G ProSe end UE and the 5G ProSe direct link is between the target 5G ProSe end UE and a 5G ProSe inter-UE relay UE, then the target UE:

[0773] a) will contain a relay reselection indication;

[0774] b) will contain the new 5G ProSe inter-UE relay UE user information ID;

[0775] c) will contain the UE IP address of the initiating 5G ProSe; and

[0776] d) shall contain the target 5G ProSe end UE IP address to be used with the newly selected 5G ProSe inter-UE relay UE (if IP communication is used).

[0777] 2) If the target UE acts as a 5G ProSe inter-UE relay UE and the 5G ProSe direct link is between the 5G ProSe inter-UE relay UE and the source 5G ProSe end UE, then the target UE:

[0778] a) will contain a relay reselection indication;

[0779] b) will contain the new 5G ProSe inter-UE relay UE user information ID;

[0780] c) will contain the target 5G ProSe UE IP address; and

[0781] d) shall contain the target 5G ProSe end UE IP address to be used with the newly selected 5G ProSe inter-UE relay UE (if IP communication is used).

[0782] Editor's Note: The ProSe Direct Link Modification Accept message needs to be updated.

[0783] If the target UE accepts the 5G ProSe direct link modification request, the target UE may perform PC5 QoS flow establishment on the 5G ProSe direct link as specified in section 7.2.7 and perform PC5 QoS flow matching on the 5G ProSe direct link as specified in section 7.2.8.

[0784] 7.2.3.4 5G ProSe Direct Link Modification Procedure by Initiating UE Completed

[0785] After receiving the ProSe Direct Link Modification Accept message, the initiating UE will stop timer T5081.

[0786] After receiving the ProSe Direct Link Modification Accept message, if the ProSe Direct Link Modification Request message is to add a new ProSe application, add a new PC5 QoS flow, or modify any existing PC5 QoS flow in the 5G ProSe direct link, the initiating UE provides the added or modified PQFI and corresponding PC5 QoS parameters and PC5 link identifier to the lower layer.

[0787] Upon receiving the ProSe direct link modification accept message, if the ProSe direct link modification request message is to remove an existing ProSe application or to remove an existing PC5 QoS flow from the 5G ProSe direct link, the initiating UE provides the removed PQFI and PC5 link identifier to the lower layer.

[0788] Upon receiving the ProSe Direct Link Modification Accept message, if the ProSe Direct Link Modification Request message is to establish a 5G ProSe inter-UE relay communication with an additional 5G ProSe layer 3-end UE using an existing 5G ProSe direct link between the 5G ProSe layer 3-end UE and the 5G ProSe layer 3 inter-UE relay UE, the initiating UE shall send a ProSe Direct Link Setup Accept message to the source 5G ProSe layer 3-end UE, as specified in Section 7.2.2.3, if the initiating UE acts as a 5G ProSe layer 3 inter-UE relay UE.

[0789] Editor's note: Whether to include and how to set the ProSe identifier for the 5G ProSe direct link between the source 5G ProSe layer 3 end UE and the 5G ProSe layer 3 inter-UE relay UE and the 5G ProSe direct link between the 5G ProSe layer 3 inter-UE relay UE and the target 5G ProSe layer 3 end UE is for further study.

[0790] Upon receipt of the ProSe Direct Link Modify Accept message containing the Relay Reselection Indication, if the ProSe Direct Link Modify Request message is for Layer 3 Inter-UE relay reselection, the initiating UE shall establish a PC5 unicast link with the selected 5G ProSe Inter-UE relay UE (if such a PC5 unicast link does not already exist) and shall create a ProSe Direct Link Modify Confirm message. In this message, the initiating UE:

[0791] a) shall contain the relay reselection indication, the IP address of the initiating 5G ProSe UE to be used with the newly selected 5G ProSe inter-UE relay UE, and the IP address of the target 5G ProSe end UE, if IP communication is used, and if:

[0792] 1) The UE acts as a source 5G ProSe UE, and the 5G ProSe direct link is between the source 5G ProSe UE and a 5G ProSe inter-UE relay UE; or

[0793] b) shall contain the relay reselection indication, the IP address of the target 5G ProSe UE to be used with the newly selected 5G ProSe inter-UE relay UE, and the IP address of the source 5G ProSe UE, if IP communication is used, and if:

[0794] 1) The UE acts as a 5G ProSe inter-UE relay UE, and the 5G ProSe direct link is between the 5G ProSe inter-UE relay UE and the target 5G ProSe end UE.

[0795] After the ProSe Direct Link Modification Confirm message is generated, the initiating UE passes this message together with the Layer 2 ID of the initiating UE for 5G ProSe direct communication and the Layer 2 ID of the target UE for 5G ProSe direct communication to the lower layer for transmission.

[0796] If the source UE confirms 5G ProSe direct link modification accept, the source UE starts receiving and / or transmitting traffic via the newly selected 5G ProSe inter-UE relay UE.

[0797] 7.2.3.5 5G ProSe Direct Link Modification Procedure Not Accepted by Target UE

[0798] If the 5G ProSe direct link modification request cannot be accepted, the target UE shall send a ProSe direct link modification reject message. The ProSe direct link modification reject message contains the PC5 signaling protocol cause IE, which is set to one of the following cause values:

[0799] #5 Lack of resources for 5G ProSe direct links;

[0800] #6 Required services are not permitted;

[0801] #12 Misalignment with security policy;

[0802] #16 Lack of local capabilities;

[0803] #20 is a 5G ProSe UE fault.

[0804] #yy Relay UE is not selected for link establishment with integrated discovery; or

[0805] #111 Unspecified protocol error.

[0806] If the target UE is not allowed to accept this request, for example, because the ProSe application to be added is not allowed according to the operator policy or configuration parameters for ProSe communication over PC5 specified in section 5.2.4, then the target UE shall send a ProSe Direct Link Modification Reject message with PC5 Signaling Protocol Cause Value #6 "Requested Service Not Allowed".

[0807] If the 5G ProSe direct link modification fails due to congestion issues or other temporary lower layer issues resulting in resource constraints, the target UE shall send a ProSe Direct Link Modification Reject message with PC5 signaling protocol cause value #5 “Lack of resources for 5G ProSe Direct Link”.

[0808] If a target UE acting as a target 5G ProSe end UE receives one or more direct link modification requests or direct link establishment requests for end-to-end connection establishment with a source 5G ProSe end UE and uses integrated discovery, the target UE shall select a 5G ProSe inter-UE relay UE and send a ProSe direct link modification reject message with PC5 signaling protocol cause value #yy "Relay UE not selected for link establishment with integrated discovery" to the 5G ProSe inter-UE relay that was not selected and that sent the ProSe direct link modification request message.

[0809] If the Link Modify Operation Code is set to "Associate new ProSe application with existing PC5 QoS flow" and the security policy corresponding to the ProSe identifier is not aligned with the security policy applied to the existing 5G ProSe direct link, the target UE shall send a ProSe Direct Link Modify Reject message with PC5 signaling protocol cause value #12 "Misaligned security policy".

[0810] If the link modification operation requires adding a new PC5 QoS flow, but the target UE is unable to support the additional packet filters that will be required on the target UE's existing PDU sessions, the target UE shall send a ProSe Direct Link Modification Reject message with PC5 signaling protocol cause value #16 "Lack of local capability".

[0811] If the target UE acts as a target 5G ProSe end UE, and the 5G ProSe direct link modification procedure is between a 5G ProSe inter-UE relay UE and a target 5G ProSe end UE, then the target 5G ProSe end UE may include, in the ProSe direct link modification reject message, a source UE information IE set to the user information ID of the source 5G ProSe end UE that has initiated the 5G ProSe direct link establishment procedure.

[0812] If the target UE acts as a 5G ProSe inter-UE relay UE, the 5G ProSe direct link modification procedure is between the source 5G ProSe side UE and the 5G ProSe inter-UE relay UE, and the target 5G ProSe side UE has rejected the 5G ProSe direct link establishment procedure or the 5G ProSe direct link modification procedure, the 5G ProSe inter-UE relay UE shall send a ProSe direct link modification reject message with a PC5 signaling protocol cause value #20 "Failure from 5G ProSe side UE" to the source 5G ProSe side UE. The 5G ProSe inter-UE relay UE may include in the ProSe direct link modification reject message a PC5 side UE failure cause IE set to the PC5 signaling protocol cause received from the target 5G ProSe side UE that rejected the 5G ProSe direct link establishment procedure, as specified in section 7.2.2.5. The 5G ProSe inter-UE relay UE may include in the ProSe direct link modification reject message a target UE information IE set to the user information ID of the target 5G ProSe side UE that rejected the 5G ProSe direct link establishment procedure.

[0813] For other reasons leading to link establishment failure, the target UE will send a ProSe Direct Link Modify Reject message with PC5 signaling protocol cause value #111 "Unspecified protocol error".

[0814] Upon receiving the ProSe Direct Link Modify Reject message, the initiating UE shall stop timer T5081 and abort the 5G ProSe Direct Link Modify procedure. If the PC5 signaling protocol cause value in the ProSe Direct Link Modify Reject message is #11 "Required service not allowed" or #5 "Lack of resources for 5G ProSe direct link" or #12 "Misaligned security policy", the initiating UE shall not attempt to initiate a 5G ProSe direct link modification with the same target UE to add the same ProSe application or add or modify the same PC5 QoS flow for at least the time period T.

[0815] NOTE: The length of the time period T is UE implementation specific and may be different when the UE receives PC5 signaling protocol cause value #11 "Required service not allowed", when the UE receives PC5 signaling protocol cause value #5 "Lack of resources for 5G ProSe direct link", or when the UE receives PC5 signaling protocol cause value #12 "Misaligned security policy". The length of the time period T is not less than 30 minutes.

[0816] 7.2.3.6 Abnormal situations

[0817] 7.2.3.6.1 Abnormal situation at the initiating UE

[0818] The following anomalies can be identified:

[0819] a) If timer T5081 expires, the initiating UE will retransmit the ProSe Direct Link Modification Request message and restart timer T5081. After reaching the maximum number of allowed retransmissions, the initiating UE will abort the 5G ProSe Direct Link Modification procedure and may notify upper layers that the target UE is unreachable.

[0820] NOTE 1: The maximum number of allowed retransmissions is UE implementation specific.

[0821] NOTE 2: After reaching the maximum number of allowed retransmissions, whether the initiating UE releases the 5G ProSe direct link depends on its implementation.

[0822] b) For the same 5G ProSe direct link, if the initiating UE receives a ProSe direct link release request message after the initiating UE requested 5G ProSe direct link modification procedure, the initiating UE shall stop timer T5081, abort the 5G ProSe direct link modification procedure, and continue with the 5G ProSe direct link release procedure.

[0823] c) For the same 5G ProSe direct link, if the initiating UE receives a ProSe Direct Link Modification Request message during the 5G ProSe Direct Link Modification procedure, the initiating UE shall stop timer T5081 and abort the 5G ProSe Direct Link Modification procedure. Subsequent processing depends on the implementation. For example, the initiating UE waits for an implementation-dependent time before initiating a new 5G ProSe Direct Link Modification procedure (if still needed).

[0824] NOTE 3: An implementation-dependent timer value may need to be set to avoid further conflicts (e.g., random timer value).

[0825] 7.2.3.6.2 Abnormal Situation at Target UE

[0826] The following anomalies can be identified:

[0827] a) For the same 5G ProSe direct link, if the target UE receives a ProSe direct link release request message during the 5G ProSe direct link modification procedure, the target UE shall stop all running timers of this 5G ProSe direct link, abort the 5G ProSe direct link modification procedure, and continue with the 5G ProSe direct link release procedure.

[0828] 7.2.3.7 5G ProSe Direct Link Modification Procedure by Target UE Completed

[0829] After receiving the ProSe direct link modification confirmation, the target 5G ProSe UE starts to receive traffic, transmit traffic, or both via the newly selected 5G ProSe inter-UE relay UE.

[0830] […]

[0831] 7.2.10 5G ProSe Direct Link Security Mode Control Procedure

[0832] 7.2.10.1 Overview

[0833] The 5G ProSe Direct Link Security Mode Control procedure is used to establish security between two UEs during the 5G ProSe Direct Link Establishment Procedure or the 5G ProSe Direct Link Key Update Procedure. If UE PC5 signaling integrity protection is not activated, security is not established. After successful completion of the 5G ProSe Direct Link Security Mode Control procedure, the selected security algorithms and their non-null associated keys are used to integrity protect and encrypt all PC5 signaling messages exchanged on this 5G ProSe direct link between the UEs, and the security context can be used to protect all PC5 user plane data exchanged on this 5G ProSe direct link between the UEs. The UE that sends the ProSe Direct Link Security Mode Command message is referred to as the "initiating UE," and the other UE is referred to as the "target UE."

[0834] 7.2.10.2 5G ProSe Direct Link Security Mode Control Procedure Initiated by the Initiating UE

[0835] The initiating UE shall meet the following prerequisites before initiating the 5G ProSe direct link security mode control procedure:

[0836] a) The target UE has initiated a 5G ProSe direct link establishment procedure towards the initiating UE by sending a ProSe direct link establishment request message, and:

[0837] 1) ProSe Direct Link Establishment Request Message:

[0838] i) contains the target user information IE, which contains the application layer ID of the originating UE; or

[0839] ii) does not contain the Target User Information IE, and the initiating UE is interested in the ProSe service identified by the ProSe identifier in the ProSe Direct Link Setup Request message; and

[0840] 2) Initiating UE:

[0841] i) If the direct communication is not between a 5G ProSe remote UE and a 5G ProSe UE to a network relay UE, then the direct communication is based on the K contained in the ProSe Direct Link Setup Request message. NRP ID identifies the existing K NRP , or export a new K NRP ;

[0842] ii) If direct communication is between a 5G ProSe Remote UE and a 5G ProSe UE to Network Relay UE, where user plane security procedures are used, then the new K is received according to the user plane security procedures specified in 3GPP TS 33.503

[34] . NRP ;

[0843] iii) If the direct communication is between a 5G ProSe remote UE and a 5G ProSe UE to network relay UE, where the control plane security procedures are used, then the new K is received according to the control plane security procedures specified in 3GPP TS 33.503

[34] . NR_ProSe ;or

[0844] iv) has decided not to activate security protection based on its UE 5G ProSe direct signaling security policy and the target UE’s 5G ProSe direct signaling security policy; or

[0845] b) The target UE has initiated the 5G ProSe direct link key update procedure towards the initiating UE by sending a ProSe direct link key update request message along with the following:

[0846] 1) If the target UE has included a re-authentication indication in the ProSe direct link key update request message, the initiating UE has derived a new K NRP .

[0847] when:

[0848] a) Direct communication is not between a 5G ProSe remote UE and a 5G ProSe UE to a network relay UE. If the new K NRP has been derived by the initiating UE; or

[0849] b) Direct communication is between a 5G ProSe remote UE and a 5G ProSe UE to a network relay UE. If a new K is received by the initiating UE according to the security procedures on the user plane or the security procedures on the control plane, respectively NRP or K NR_ProSe , as specified in 3GPP TS 33.503

[34] ;

[0850] The initiating UE will generate KNRP The 2 MSBs of ID are used to ensure that the resulting K NRP The ID will be unique within the originating UE.

[0851] NOTE 1: If the direct communication is not between a 5G ProSe remote UE and a 5G ProSe UE to a network relay UE, then K NRP ID remains corresponding to K NRP If the direct communication is between a 5G ProSe remote UE and a 5G ProSe UE to a network relay UE, then K NRP ID remains corresponding to K NRP (if security procedures on the user plane are used) or K NR_ProSe The ID of the control plane security program (if using).

[0852] The initiating UE shall select a security algorithm based on its UE 5G ProSe direct signaling security policy and the target UE's 5G ProSe direct signaling security policy. If the 5G ProSe direct link security mode control procedure is triggered during the 5G ProSe direct link establishment procedure, then the initiating UE shall not select the null integrity protection algorithm if the 5G ProSe direct signaling integrity protection policy of either the initiating UE or the target UE is set to "signaling integrity protection required". If the 5G ProSe direct link security mode control procedure is triggered during the 5G ProSe direct link key update procedure, then the initiating UE:

[0853] a) If the integrity protection algorithm currently used for the 5G ProSe direct link is different from the null integrity protection algorithm, the null integrity protection algorithm shall not be selected;

[0854] b) If the encryption protection algorithm currently used for the 5G ProSe direct link is different from the null encryption protection algorithm, the null encryption protection algorithm shall not be selected;

[0855] c) if the currently used integrity protection algorithm is the null integrity protection algorithm, then the null integrity protection algorithm will be selected; and

[0856] d) If the encryption protection algorithm currently in use is the null encryption protection algorithm, then the null encryption protection algorithm will be selected.

[0857] Next, the initiating UE will:

[0858] a) If the direct communication is not between a 5G ProSe remote UE and a 5G ProSe UE to a network relay UE:

[0859] 1) Generate a 128-bit Nonce_2 value;

[0860] 2) Nonce_1 and K received in the ProSe direct link establishment request message NRP and Nonce_2 to derive K NRP-sess , as specified in 3GPP TS 33.536

[37] ; and

[0861] 3) From K NRP-sess and the selected security algorithm to derive the NR PC5 encryption key NRPEK and the NR PC5 integrity key NRPIK as specified in 3GPP TS 33.536

[37] ;

[0862] b) If the direct communication is between a 5G ProSe Remote UE and a 5G ProSe UE to Network Relay UE and the security procedures on the control plane specified in 3GPP TS 33.503

[34] are used:

[0863] 1) From the K received in the ProSe Direct Link Setup Request message NR_ProSe , Nonce_2 and Nonce_1 derive K relay-sess , as specified in 3GPP TS 33.503

[34] ; and

[0864] 2) From K relay-sess and the selected security algorithm to derive the NR PC5 encryption key K relay-enc and NR PC5 integrity key K relay-int , as specified in 3GPP TS 33.503

[34] ; or

[0865] c) If the direct communication is between a 5G ProSe Remote UE and a 5G ProSe UE to Network Relay UE and the security procedures on the user plane specified in 3GPP TS 33.503

[34] are used:

[0866] 1) From the K received in the ProSe Direct Link Setup Request message NRP , K NRP Freshness parameter 2 and K NRP Freshness parameter 1 derives K NRP-sess , as specified in 3GPP TS 33.503

[34] ; and

[0867] 2) From K NRP-sess and the selected security algorithm to derive the NR PC5 encryption key NRPEK and the NR PC5 integrity key NRPIK as specified in 3GPP TS 33.503

[34] ; and

[0868] d) Create a ProSe Direct Link Security Mode Command message. In this message, the initiating UE:

[0869] 1) The key establishment information container IE will be included, provided that the 5G ProSe direct link is not used for direct communication between the 5G ProSe remote UE and the 5G ProSe UE to the network relay UE, and the new K has been derived at the initiating UE NRP , and is used to generate K NRP The authentication method requires sending information to complete the 5G ProSe direct link authentication procedure;

[0870] NOTE 2: The key establishment information container is provided by the upper layer.

[0871] 2) will include K NRP MSB of ID IE, provided that the new K has been derived NRP Or a new K has been received at the initiating UE NRP or K NR_ProSe ;

[0872] 3) Will contain Nonce_2IE, which:

[0873] i) When the direct communication is not between a 5G ProSe remote UE and a 5G ProSe UE to a network relay UE, it is set to a 128-bit temporary value generated by the initiating UE;

[0874] ii) When direct communication is between a 5G ProSe Remote UE and a 5G ProSe UE to network relay UE and the security procedures on the user plane specified in 3GPP TS 33.503

[34] are used, set to the K received by the initiating UE NRP Freshness parameter 2 value; or

[0875] iii) when direct communication is between a 5G ProSe Remote UE and a 5G ProSe UE to a network relay UE and the security procedures on the control plane specified in 3GPP TS 33.503

[34] are used, set to the Nonce_2 value received by the initiating UE;

[0876] for the purpose of establishing session keys on this 5G ProSe direct link if the selected integrity protection algorithm is not the null integrity protection algorithm;

[0877] 4) will include the selected security algorithm;

[0878] 5) including the UE security capabilities received from the target UE in the ProSe direct link setup request message or the ProSe direct link key update request message;

[0879] 6) Include the UE 5G ProSe direct signaling security policy received from the target UE in the ProSe direct link establishment request message;

[0880] 7) If the selected integrity protection algorithm is not the Null Integrity Protection Algorithm, then it shall contain the K selected by the originating UE as specified in 3GPP TS 33.536

[37] NRP-sess LSB of ID;

[0881] NOTE 3: If the direct communication is not between a 5G ProSe remote UE and a 5G ProSe UE to a relay UE in the network, then K NRP-sess ID remains corresponding to K NRP-sess If the direct communication is between a 5G ProSe remote UE and a 5G ProSe UE to a network relay UE, then K NRP-sess ID remains corresponding to K NRP-sess (if security procedures on the user plane are used) or K relay-sess The ID of the control plane security program (if using).

[0882] 8) When direct communication is between a 5G ProSe Remote UE and a 5G ProSe UE to Network Relay UE, the GPI shall be included if received from the 5G PKMF according to the security procedures on the user plane specified in 3GPP TS 33.503

[34] ; and

[0883] 9) When direct communication is between a 5G ProSe Remote UE and a 5G ProSe UE to network Relay UE, an EAP message shall be included if received from the network according to the security procedures on the control plane specified in 3GPP TS 33.503

[34] .

[0884] If the security protection of this 5G ProSe direct link is activated by using a non-null integrity protection algorithm or a non-null ciphering protection algorithm, the initiating UE will receive the K received in the ProSe Direct Link Setup Request message or the ProSe Direct Link Key Update Request message. NRP-sess The MSB of the ID and the K contained in the ProSe direct link security mode command message NRP-sess The LSB of ID forms K NRP-sess ID. The initiating UE will use K NRP-sess ID to identify the new security context.

[0885] The initiating UE shall set the source Layer 2 ID and the destination Layer 2 ID as follows:

[0886] 1) If the originating UE acts as a relay UE for a 5G ProSe layer 3 UE to the network and uses an EAP-AKA' based authentication method as specified in section 6.3.3.3 of 3GPP TS 33.503

[34] ,

[0887] Set the source layer 2 ID to the source layer 2 ID used for the ProSe AA message transmission request message, and set the destination layer 2 ID to the destination layer 2 ID used for the ProSe AA message transmission request message;

[0888] 2) If the initiating UE does not act as a relay UE from the 5G ProSe UE to the network and the 5G ProSe direct link authentication procedure has been initiated:

[0889] Set the source layer 2 ID to the source layer 2 ID for the ProSe direct link authentication request message, and set the destination layer 2 ID to the destination layer 2 ID for the ProSe direct link authentication request message;

[0890] 3) Otherwise, assign a source Layer 2 ID by itself and set the destination Layer 2 ID to the source Layer 2 ID in the ProSe Direct Link Setup Request message.

[0891] NOTE 4: The UE implementation ensures that any value of the self-assigned source Layer-2 ID is different from any other self-assigned source Layer-2 ID used for 5G ProSe direct discovery as specified in sections 6.2.14, 6.2.15 and 8.2.1, and different from any other provided destination Layer-2 ID as specified in section 5.2.

[0892] NOTE 5: The target UE may reuse the Layer 2 ID that the target UE used in a previous 5G ProSe direct link with the same peer UE.

[0893] After the ProSe Direct Link Security Mode Command message is generated, the initiating UE passes this message along with the following to the lower layer for transmission: Source Layer 2 ID and Destination Layer 2 ID, NRPIK (or K relay-Int , where applicable), NRPEK (or K relay-enc , where applicable) (if applicable), K NRP-sess The initiating UE shall send a new ProSe Direct Link Security Mode Command message to the target UE while the timer T5089 is running.

[0894] NOTE 6: The ProSe Direct Link Security Mode Command message is integrity protected (and unencrypted) at the lower layers using the new security context. If the 5G ProSe Direct Link Security Mode Control procedure is triggered during the 5G ProSe Direct Link Key Update procedure, the initiating UE shall provide an indication of activation of 5G ProSe direct user plane security protection for the 5G ProSe direct link with the new security context to the lower layers (if applicable), along with the Layer 2 ID of the initiating UE for 5G ProSe direct communication and the Layer 2 ID of the target UE for 5G ProSe direct communication.

[0895] [3GPP TS 24.554 V18.1.0 titled "5G ProSe direct link security mode control procedure" Figure 7 .2.10.2.1 Reproduced as Figure 20 ]

[0896] 7.2.10.3 5G ProSe Direct Link Security Mode Control Procedure Accepted by Target UE

[0897] Upon receiving the ProSe Direct Link Security Mode Command message, if the newly assigned initiating UE Layer 2 ID is included and if the 5G ProSe Direct Link authentication procedure has not yet been performed, the target UE will replace the original initiating UE Layer 2 ID with the newly assigned initiating UE Layer 2 ID for 5G ProSe direct communication. The target UE will verify the Selected Security Algorithm IE contained in the ProSe Direct Link Security Mode Command message. If "Null Integrity Algorithm" is included in the Selected Security Algorithm IE, integrity protection is not provided for this 5G ProSe direct link, and signaling messages are transmitted without protection. If "Null Ciphering Algorithm" and an integrity algorithm other than "Null Integrity Algorithm" are included in the Selected Algorithm IE, ciphering protection is not provided for this 5G ProSe direct link, and signaling messages are transmitted without protection. If the target UE's 5G ProSe direct signaling integrity protection policy is set to "Signaling Integrity Protection Required", the target UE will verify that the Selected Security Algorithm IE in the ProSe Direct Link Security Mode Command message does not contain a null integrity protection algorithm. If the Selected Integrity Protection Algorithm is not a null integrity protection algorithm, the target UE will:

[0898] a) If the direct communication is not between a 5G ProSe remote UE and a 5G ProSe UE to a network relay UE:

[0899] 1) From the K received in the ProSe Direct Link Security Mode Command message NRP , Nonce_1 and Nonce_2 derive K NRP-sess, as specified in 3GPP TS 33.536

[37] ;

[0900] 2) From K NRP-sess and the selected integrity algorithm to derive the NRPIK, as specified in 3GPP TS 33.536

[37] ; and

[0901] 3) If K is derived NRP-sess And the selected encryption protection algorithm is not the null encryption protection algorithm, then the target UE will NRP-sess and the selected encryption algorithm to derive the NRPEK, as specified in 3GPP TS 33.536

[37] ; or

[0902] b) If the direct communication is between a 5G ProSe remote UE and a 5G ProSe UE to network relay UE:

[0903] 1) If the control plane security procedures specified in 3GPP TS 33.503

[34] are used, K is derived according to the control plane security procedures. relay-sess , and from K relay-sess and the selected integrity algorithm to derive K relay-int , as specified in 3GPP TS 33.503

[34] . If K relay-sess If the encryption protection algorithm is not the null encryption protection algorithm, the target UE will select K relay-sess and the selected encryption algorithm to derive K relay-enc , as specified in 3GPP TS 33.503

[34] ; or

[0904] 2) If the user plane security procedures specified in 3GPP TS 33.503

[34] are used, K is derived according to the user plane security procedures. NRP-sess , and from K NRP-sess and the selected integrity algorithm to derive the NRPIK, as specified in 3GPP TS 33.503

[34] . If K NRP-sess If the encryption protection algorithm is not the null encryption protection algorithm, the target UE will select K NRP-sess and the selected encryption algorithm to derive the NRPEK, as specified in 3GPP TS 33.503

[34] .

[0905] The target UE determines whether it can accept the ProSe Direct Link Security Mode Command message by performing the following operations:

[0906] a) If the 5G ProSe direct signaling integrity protection policy of the target UE is set to "signaling integrity protection required", then verify that the Selected Security Algorithm IE in the ProSe Direct Link Security Mode Command message does not contain a null integrity protection algorithm;

[0907] b) If the selected integrity protection algorithm is not the null integrity protection algorithm, the lower layer is required to use NRPIK (or K relay-int , when applicable) and the selected integrity protection algorithm to verify the integrity of the ProSe direct link security mode command message;

[0908] c) verifying that the received UE security capabilities have not changed compared to the values ​​sent by the target UE to the initiating UE in the ProSe Direct Link Setup Request message or the ProSe Direct Link Key Update Request message;

[0909] d) If the 5G ProSe direct link security mode control procedure is triggered during the 5G ProSe direct link establishment procedure,

[0910] 1) verifying that the received UE 5G ProSe direct signalling security policy has not been changed compared to the value sent by the target UE to the initiating UE in the ProSe Direct Link Setup Request message; and

[0911] 2) Check K contained in the ProSe direct link security mode command message NRP-sess The LSBs of the ID are not set to the same values ​​as those received from another UE in response to the target UE's ProSe Direct Link Setup Request message; and

[0912] e) If the 5G ProSe direct link security mode control procedure is triggered during the 5G ProSe direct link key update procedure and the integrity protection algorithm currently used for the 5G ProSe direct link is different from the null integrity protection algorithm, then verify that the selected security algorithm IE in the ProSe direct link security mode command message does not include the null integrity protection algorithm.

[0913] If the target UE does not include K in the ProSe Direct Link Setup Request message NRP ID, the target UE includes a re-authentication indication in the ProSe Direct Link Key Update Request message or the initiating UE has chosen to derive:

[0914] a) New K NRP , if the direct communication is not between a 5G ProSe remote UE and a 5G ProSe UE to a relay UE in the network, then the target UE will derive K NRP , as specified in 3GPP TS 33.536

[37] ;

[0915] b) New K NRP , if the direct communication is between a 5G ProSe remote UE and a 5G ProSe UE to network relay UE and the security procedures on the user plane specified in 3GPP TS 33.503

[34] are used, then the target UE shall derive K NRP , as specified in 3GPP TS 33.536

[37] ; or

[0916] c) New K NR_ProSe , if the direct communication is between a 5G ProSe remote UE and a 5G ProSe UE to network relay UE and the security procedures on the control plane specified in 3GPP TS 33.503

[34] are used, then the target UE shall derive K NR_ProSe , as specified in 3GPP TS 33.536

[37] ; and

[0917] The target UE will select K NRP The 2 LSBs of ID are used to ensure that the resulting K NRP The ID will be unique in the target UE. The target UE will receive the K NRP MSB of ID and its selected K NRP The 2 LSBs of ID form K NRP ID, and will store NRP / K NR_ProSe The complete K NRP ID.

[0918] NOTE 1: If the direct communication is not between a 5G ProSe remote UE and a 5G ProSe UE to a network relay UE, then K NRP ID remains corresponding to K NRP If the direct communication is between a 5G ProSe remote UE and a 5G ProSe UE to a network relay UE, then K NRP ID remains corresponding to K NRP (if security procedures on the user plane are used) or K NR_ProSe The ID of the control plane security program (if using).

[0919] If GPI is included in the ProSe Direct Link Security Mode Command message and the direct communication is between a 5G ProSe Remote UE and a 5G ProSe UE to Network Relay UE, then according to the security procedures on the user plane specified in 3GPP TS 33.503

[34] , the target UE shall derive UP-PRUK from GPI and obtain UP-PRUK ID, and use UP-PRUK to derive KNRP .

[0920] If the target UE accepts the ProSe Direct Link Security Mode Command message, the target UE will create a ProSe Direct Link Security Mode Complete message. In this message, the target UE:

[0921] a) If the 5G ProSe direct link security mode control procedure is triggered during the 5G ProSe direct link establishment procedure:

[0922] 1) If the 5G ProSe direct link is not used for 5G ProSe direct communication between a 5G ProSe remote UE and a 5G ProSe UE to a network relay UE, then the PQFI and corresponding PC5QoS parameters shall be included; or

[0923] 2) If the 5G ProSe direct link is used for 5G ProSe direct communication between a 5G ProSe Layer 3 remote UE and a 5G ProSe Layer 3 UE to a network relay UE, then the PQFI and corresponding PC5 QoS parameters may be included;

[0924] NOTE 2: If the 5G ProSe direct link is used for 5G ProSe direct communication between a 5G ProSe Layer 2 remote UE and a 5G ProSe Layer 2 UE to a network relay UE, the PQFI and corresponding PC5 QoS parameters are not included.

[0925] b) If IP communication is used and the 5G ProSe direct link security mode control procedure is triggered during the 5G ProSe direct link establishment procedure, then the IP address configuration IE set to one of the following values ​​shall be included:

[0926] 1) "IPv6 router", provided that only IPv6 address allocation mechanisms are supported by the target UE, i.e. acting as an IPv6 router;

[0927] 2) "DHCPv4 server", provided that only IPv4 address allocation mechanism is supported by the target UE, i.e., acting as a DHCPv4 server;

[0928] 3) "DHCPv4 server and IPv6 router", provided that both IPv4 and IPv6 address allocation mechanisms are supported by the target UE; or

[0929] 4) Address allocation not supported”, if both IPv4 and IPv6 address allocation mechanisms are not supported by the target UE;

[0930] NOTE 3: If Ethernet or Unstructured Data Unit Type is used for communication, then the UE does not include the IP Address Configuration IE nor the Link-Local IPv6 Address IE.

[0931] c) If IP communication is used, the IP Address Configuration IE is set to “Address Allocation Not Supported” and the 5G ProSe Direct Link Security Mode Control procedure is triggered during the 5G ProSe Direct Link Establishment procedure, then the Link-Local IPv6 Address IE formed locally based on IETF RFC4862

[25] shall be included;

[0932] d) If the new K is derived NRP Or receive a new K NRP or K NR_ProSe , then it will contain K NRP The 2 LSBs of the ID; and

[0933] e) If the 5G ProSe direct link security mode control procedure is triggered during the 5G ProSe direct link establishment procedure, then its UE 5G ProSe direct user plane security policy for this 5G ProSe direct link shall be included. In the case where different ProSe services are mapped to different 5G ProSe direct user plane security policies, when more than one ProSe identifier is included in the ProSe Direct Link Setup Request message, each of the user plane security policies of those ProSe services shall be compatible, for example, "user plane integrity protection not required" and "user plane integrity protection required" are not compatible.

[0934] If the selected integrity protection algorithm is not the Null Integrity Protection Algorithm, the target UE will use the K NRP-sess The MSB of the ID and the K received in the ProSe Direct Link Security Mode Command message NRP-sess The LSB of ID forms K NRP-sess ID. The target UE will use K NRP-sess ID to identify the new security context.

[0935] After the ProSe Direct Link Security Mode Complete message is generated, the target UE passes this message to the lower layer for transmission along with the following: the layer 2 ID of the target UE for 5G ProSe direct communication and the layer 2 ID of the initiating UE for 5G ProSe direct communication, the NRPIK (or K relay-int , where applicable), NRPEK (or K relay-enc , where applicable) (if applicable), K NRP-sessID, the selected security algorithm as specified in 3GPP TS 33.536

[37] and an indication of activation of 5G ProSe direct signaling security protection for the 5G ProSe direct link with the new security context (if applicable).

[0936] NOTE 4: The ProSe Direct Link Security Mode Complete message and other 5G ProSe direct signaling messages are integrity protected and encrypted (if applicable) using a new security context at the lower layer.

[0937] If the 5G ProSe direct link security mode control procedure is triggered during the 5G ProSe direct link key update procedure, the target UE shall provide to the lower layers an indication of activation of 5G ProSe direct user plane security protection for the 5G ProSe direct link with a new security context (if applicable), along with the Layer 2 ID of the initiating UE for 5G ProSe direct communication and the Layer 2 ID of the target UE for 5G ProSe direct communication.

[0938] 7.2.10.4 Completion of 5G ProSe Direct Link Security Mode Control Procedure by Initiating UE

[0939] After receiving the ProSe Direct Link Security Mode Complete message, the initiating UE stops timer T5089. If the selected integrity protection algorithm is not the Null Integrity Protection Algorithm, the UE verifies the integrity of the ProSe Direct Link Security Mode Complete message. If the integrity check passes, the initiating UE continues the procedure that triggered the 5G ProSe Direct Link Security Mode Control procedure. If the selected integrity protection algorithm is the Null Integrity Protection Algorithm, the UE continues the procedure without verifying integrity protection.

[0940] After receiving the ProSe Direct Link Security Mode Complete message, the initiating UE will delete the old security context it has for the target UE (if any).

[0941] 7.2.10.5 5G ProSe Direct Link Security Mode Control Procedure Not Accepted by Target UE

[0942] If the ProSe Direct Link Security Mode Command message cannot be accepted, the target UE shall send a ProSe Direct Link Security Mode Reject message and the target UE shall abort the ongoing procedure that triggered the initiation of the 5G ProSe Direct Link Security Mode Control procedure, unless the ongoing procedure is a 5G ProSe Direct Link Establishment procedure and the target user information is not included in the ProSe Direct Link Establishment Request message. The ProSe Direct Link Security Mode Reject message contains the PC5 Signaling Protocol Cause IE, which indicates one of the following cause values:

[0943] #5: Lack of resources for 5G ProSe direct links;

[0944] #7: Integrity failure;

[0945] #8: UE security capability mismatch;

[0946] #9: K NRP-sess LSB conflict of ID;

[0947] #10: UE PC5 unicast signaling security policy mismatch;

[0948] #14: Authentication synchronization error; or

[0949] #111: Unspecified protocol error.

[0950] If this 5G ProSe Direct Link Security Mode Control procedure is triggered during the 5G ProSe Direct Link Establishment procedure and the implementation-specific maximum number of established NR 5G ProSe direct links has been reached, the target UE shall send a ProSe Direct Link Security Mode Reject message with PC5 signaling protocol cause value #5 "Lack of resources for 5G ProSe Direct Link".

[0951] If the ProSe Direct Link Security Mode Command message cannot be accepted because the 5G ProSe Direct Link Security Mode Control procedure is triggered during the 5G ProSe Direct Link Establishment procedure, the Selected Security Algorithm IE in the ProSe Direct Link Security Mode Command message contains a null integrity protection algorithm, and the 5G ProSe direct signaling integrity protection policy of the target UE is set to "Signaling Integrity Protection Required", then the target UE shall include PC5 signaling protocol cause #10 "UE PC5 unicast signaling security policy mismatch" in the ProSe Direct Link Security Mode Reject message.

[0952] If the ProSe Direct Link Security Mode Command message cannot be accepted because the 5G ProSe Direct Link Security Mode Control procedure is triggered during the 5G ProSe Direct Link Key Update procedure, the integrity protection algorithm currently used for the 5G ProSe direct link is different from the Null Integrity Protection Algorithm, and the Selected Security Algorithm IE in the ProSe Direct Link Security Mode Command message contains the Null Integrity Protection Algorithm, then the target UE shall include PC5 signaling protocol cause #10 "UE PC5 unicast signaling security policy mismatch" in the ProSe Direct Link Security Mode Reject message.

[0953] If the target UE detects that the UE security capabilities received in the ProSe Direct Link Security Mode Command message have changed compared to the most recent value sent by the target UE to the initiating UE in the ProSe Direct Link Setup Request message or the ProSe Direct Link Key Update Request message, the target UE shall include PC5 signaling protocol cause #8 "UE security capability mismatch" in the ProSe Direct Link Security Mode Reject message.

[0954] If the target UE detects that the K NRP-sess If the LSBs of the ID are set to the same value as those received from another UE in response to the target UE's ProSe Direct Link Setup Request message, the target UE shall include PC5 signaling protocol cause #9 "K NRP-sess LSB of ID conflict".

[0955] If the 5G ProSe Direct Link Security Mode Control procedure is used for direct communication between a 5G ProSe Remote UE and a 5G ProSe UE-to-network Relay UE, and the ProSe Direct Link Security Mode Command message cannot be accepted due to a synchronization error in processing the authentication vector (if any) contained in the GPI sent by the 5G ProSe UE-to-network Relay UE to the 5G ProSe Remote UE, then the target UE shall include PC5 signaling protocol cause #14 "Authentication Synchronization Error" in the ProSe Direct Link Security Mode Reject message and shall include the RAND and AUTS parameters in the ProSe Direct Link Security Mode Reject message.

[0956] After the ProSe direct link security mode reject message is generated, the target UE passes this message together with the layer 2 ID of the initiating UE for 5G ProSe direct communication and the layer 2 ID of the target UE for 5G ProSe direct communication to the lower layer for transmission.

[0957] After receiving the ProSe Direct Link Security Mode Reject message, the initiating UE shall stop timer T5089 and provide an indication to the lower layers to deactivate 5G ProSe Direct Security protection and delete the security context for the 5G ProSe direct link (if applicable):

[0958] a) If the PC5 signaling protocol cause IE in the ProSe Direct Link Security Mode Reject message is set to #9 "K NRP-sess LSB of ID conflicts", then retransmit K NRP-sess The ProSe direct link security mode command message has a different value for the LSB of the ID and restarts the timer T5089;

[0959] b) if the PC5 Signalling Protocol Cause IE in the ProSe Direct Link Security Mode Reject message is set to #14 “Authentication Synchronisation Error”, the message contains RAND and AUTS, and the 5G ProSe Direct Link Security Mode Control procedure is for direct communication between a 5G ProSe Remote UE and a 5G ProSe UE to Network Relay UE, then fresh GPI may be extracted from the PKMF by sending a Key Request message containing RAND and AUTS, as specified in 3GPP TS 33.503

[34] ; or

[0960] c) If the PC5 signaling protocol reason IE is set to other than #9 "K NRP-sess If the value is other than "LSB collision of ID" and other than #14 "Authentication synchronization error", the ongoing procedure that triggered the initiation of the 5G ProSe direct link security mode control procedure is aborted.

[0961] 7.2.10.6 Abnormal situations

[0962] 7.2.10.6.1 Abnormal situation at the initiating UE

[0963] a) Timer T5089 expires.

[0964] The initiating UE shall retransmit the ProSe Direct Link Security Mode Command message and restart the timer T5089. After reaching the maximum number of allowed retransmissions, the initiating UE shall abort the 5G ProSe Direct Link Security Mode Control procedure, provide an indication to the lower layers to deactivate 5G ProSe Direct Security protection and delete the security context for the 5G ProSe direct link (if applicable), and abort the ongoing procedure that triggered the initiation of the 5G ProSe Direct Link Security Mode Control procedure.

[0965] NOTE 1: The maximum number of allowed retransmissions is UE implementation specific.

[0966] b) This 5G ProSe direct link does not need to be used any more before the 5G ProSe direct link security mode control procedure is completed.

[0967] The initiating UE shall abort the procedure, shall provide an indication to lower layers to deactivate 5G ProSe Direct Security protection and delete the security context for the 5G ProSe direct link (if applicable), and shall abort the ongoing procedure that triggered the initiation of the 5G ProSe Direct Link Security Mode Control procedure.

[0968] c) If the ProSe direct link modification request message or the ProSe direct link identifier update request message is received while the timer T5089 is running, the initiating UE shall discard the ProSe direct link modification request message or the ProSe direct link identifier update request message.

[0969] d) For the same 5G ProSe direct link, if the ProSe direct link release request message is received while timer T5089 is running, the initiating UE shall stop timer T5089, abort the 5G ProSe direct link security mode control procedure, and continue with the 5G ProSe direct link release procedure.

[0970] NOTE 2: The exception cases described in item number c) or d) only occur when the 5G ProSe Direct Link Security Mode Control procedure is used to establish security between two UEs during the 5G ProSe Direct Link Key Update procedure.

[0971] Generally speaking, 3GPP TS 23.304 describes support for inter-UE relay. That is, when two (Layer 2 or Layer 3) Proximity-Based Service (ProSe) UEs are unable to communicate directly with each other, a relay UE can be used to support communication between the two UEs. The inter-UE relay UE establishes a PC5 unicast link (e.g., also known as a PC5 connection, Layer 2 link, direct link, PC5 link, etc.) with each of the two ProSe UEs, including a source ProSe UE (e.g., on a first PC5 hop) and a target ProSe UE (e.g., on a second PC5 hop), for forwarding traffic related to the ProSe service between the two ProSe UEs. If multiple source ProSe UEs want to communicate with one target ProSe UE, the PC5 link between the inter-UE relay UE and the target ProSe UE can be shared, while PC5 links can be established separately between the source ProSe UE and the inter-UE relay UE. To establish a PC5 link, either the Layer 2 Link Establishment Procedure without Integrated Discovery as specified in Section 6.7.1 of 3GPP TS 23.304 or the Layer 2 Link Establishment Procedure with Integrated Discovery as specified in Section 6.7.3 of 3GPP TS 23.304 may be used (i.e., the former may be used if the Layer 2 Link Establishment Procedure is initiated towards a relay UE or the source UE has selected a specific relay UE, and the latter may be used if the Layer 2 Link Establishment Procedure is initiated towards any relay UE or the source UE has not yet discovered any relay UE). For a shared PC5 link, a Layer 2 Link Modification Procedure will be used. However, it is unclear how to initiate the Layer 2 Link Modification Procedure when multiple source UEs are communicating with a single target UE.

[0972] For example, the first source UE may send a first direct communication request (DCR) message. The first DCR message may contain user information of the first source UE, first user information of the target UE, user information of the relay UE, a relay service code, etc. The source UE may obtain the first user information during the relay UE discovery procedure, or it may communicate with the target UE in a previous direct communication between the first source UE and the target UE. The first DCR message may be received by the relay UE. Then, the relay UE may send a second DCR message addressed to a broadcast address (i.e., a broadcast layer 2 ID predefined or preconfigured in both the relay UE and the target UE) or a layer 2 ID associated with the target UE. The second DCR message may contain user information of the first source UE, user information of the relay UE, first user information of the target UE, a relay service code, etc. The target UE may receive the second DCR message. In response to receiving the second DCR message, the target UE may establish a second-hop PC5 link with the relay UE. Similarly, the relay UE may then further establish a first 1-hop PC5 link with the first source UE, so that the first source UE and the target UE may communicate with each other via the relay UE.

[0973] The second source UE may be able to send a third DCR message. The third DCR message may contain the user information of the second source UE, the second user information of the target UE, the user information of the relay UE, the relay service code, etc. The relay UE can receive the third DCR message. However, the relay UE may not be aware that the first user information and the second user information belong to the same target UE. Therefore, the relay UE may still send a fourth DCR message that is also addressed to the broadcast address. The fourth DCR message may contain the user information of the second source UE, the user information of the relay UE, the second user information of the target UE, the relay service code, etc. For this purpose, the target UE can establish another PC5 link with the relay UE to communicate with the second source UE via the relay UE. Because using a shared PC5 link is beneficial in terms of resource efficiency, it is possible to consider that the relay UE initiates a layer 2 link modification procedure with the target UE in some way instead of initiating a layer 2 link establishment procedure.

[0974] The target UE can recognize that the fourth DCR message itself is based on the second user information of the target UE contained in this DCR message. Therefore, the target UE can send a PC5-S message to the relay UE in response to receiving the fourth DCR message (if the target UE wants to reuse the second-hop PC5 link with the relay UE). In addition to including the user information of the second source UE in the PC5-S message, the PC5-S message can also include the first user information of the target UE, so that the relay UE can know that these two user information are associated with a single target ProSe UE (i.e., the target UE). The PC5-S message can further include the second user information of the target UE. In the case where the user information of the target ProSe UE contained in the fourth DCR message is not any user information belonging to or associated with the target UE, the target UE can ignore / discard the fourth DCR message.

[0975] In response to receiving the PC5-S message from the target UE, the relay UE may initiate a Layer 2 link modification procedure toward the target UE. The relay UE may send a Link Modification Request (LMR) message to the target UE over the second-hop PC5 link. The LMR message may include user information of the second source UE, second user information of the target UE, a relay service code, and the like. The target UE may respond with a Link Modification Accept (LMA) message over the second-hop PC5 link to the relay UE.

[0976] In response to receiving the LMA message from the target UE, the relay UE may establish a second first-hop PC5 link with the second source UE. More specifically, the PC5-S message may include a cause value instructing the relay UE to (reconsider) initiating a Layer 2 link modification procedure. The PC5-S message may be a direct communication rejection message or a ProSe direct link establishment rejection message.

[0977] In one embodiment, the first-hop PC5 link may be a PC5 connection established between the source ProSe end UE and the inter-UE relay UE, and the second-hop PC5 link may be a PC5 connection established between the inter-UE relay UE and the target ProSe end UE.

[0978] In one embodiment, the user information may be a user information ID, an application layer ID, or an upper layer ID.

[0979] Figure 2121 is a flowchart of a method for a relay UE. In step 2105, the relay UE sends or broadcasts a first message to establish a PC5 connection with the relay UE for communicating with a first source UE via the relay UE. In step 2110, the relay UE receives a second message from the target UE to complete the PC5 connection. In step 2115, the relay UE sends or broadcasts a third message to establish another PC5 connection with the relay UE for communicating with a second source UE via the relay UE, wherein the third message includes second user information of the target ProSe UE. In step 2120, the relay UE receives a fourth message from the target UE, wherein the fourth message includes information indicating that the second user information belongs to or is associated with the target UE. In step 2125, in response to receiving the fourth message, the relay UE sends a fifth message to the target UE to modify the PC5 connection.

[0980] In one embodiment, the first message may include the first user information of the target UE, the user information of the first source UE, the user information of the relay UE, the relay service code, etc. The second message may include the first user information of the target UE, the user information of the relay UE, the relay service code, etc. The third message may include the user information of the second source UE, the user information of the relay UE, the relay service code, etc. The fourth message may include the first user information, the second user information, the user information of the first source UE, the user information of the second source UE, the user information of the relay UE, the relay service code, a cause value, etc. The fifth message may include the second user information, the user information of the second source UE, the relay service code, etc.

[0981] In one embodiment, the first / third message may be a direct communication request message or a ProSe direct link establishment request message. The second message may be a direct communication accept message or a ProSe direct link establishment accept message. The fourth message may be a direct communication reject message or a ProSe direct link establishment reject message. The fifth message may be a link modification request message or a ProSe direct link modification request message.

[0982] In one embodiment, the first / second source UE or target UE may be a 5G ProSe UE, and the relay UE may be a 5G ProSe inter-UE relay UE.

[0983] In one embodiment, the cause value may indicate that the relay UE initiates a link modification procedure toward the target UE. The link modification procedure may be to add a second source UE to the PC5 connection. The user information may be a user information ID or an application layer ID.

[0984] Return Reference Figure 3 and 4In one example from the perspective of a relay UE, the relay UE 300 includes program code 312 stored in a memory 310. The CPU 308 can execute the program code 312 to enable the relay UE to: (i) send or broadcast a first message to establish a PC5 connection with the relay UE for communicating with a first source UE via the relay UE; (ii) receive a second message from a target UE to complete the PC5 connection; (iii) send or broadcast a third message to establish another PC5 connection with the relay UE for communicating with a second source UE via the relay UE, wherein the third message includes second user information of the target ProSe UE; (iv) receive a fourth message from the target UE, wherein the fourth message includes information indicating that the second user information belongs to or is associated with the target UE; and (v) in response to receiving the fourth message, send a fifth message to the target UE to modify the PC5 connection. In addition, the CPU 308 can execute the program code 312 to perform all of the above actions and steps or other actions and steps described herein.

[0985] Alternatively, once the target UE establishes the second-hop PC5 link with the relay UE / after the target UE establishes the second-hop PC5 link with the relay UE / when the target UE establishes the second-hop PC5 link with the relay UE / if the target UE establishes the second-hop PC5 link with the relay UE, the target UE may provide one or more user information belonging to or associated with the target UE to the relay UE via, for example, a PC5-S message (e.g., a direct communication request / accept message, a link modification request / accept message, a link identifier update request / response / confirmation message, etc.). Given the one or more user information belonging to or associated with the target UE, the relay UE may determine whether to initiate a layer 2 link establishment procedure or a link modification procedure toward the target UE when the relay UE receives the third DCR message from the second source UE. That is, if the user information of the target ProSe end UE contained in the third DCR message can match any of the one or more user information belonging to the target end UE or associated with the target end UE, then the relay UE can initiate a link modification procedure towards the target end UE; otherwise, the relay UE can initiate a layer 2 link establishment procedure.

[0986] On the other hand, the third source UE may be able to initiate a service with an unspecified target ProSe UE. In this case, the third source UE may send a fifth DCR message that does not contain any user information of the target ProSe UE. The relay UE may receive the fifth DCR message and then send a sixth DCR message addressed to the broadcast address. The target UE may also receive the sixth DCR message from the relay UE and may be interested in communicating with the third source UE. If the target UE also considers reusing the second-hop PC5 link to communicate with the third source UE via the relay UE, the target UE may apply the above solution for the relay UE to initiate a Layer 2 link modification procedure. Regarding latency reduction, if the relay UE receives a DCR message from the source ProSe UE that does not indicate a specific target ProSe UE, the relay UE may not only initiate a Layer 2 link establishment procedure (for broadcasting a second-hop DCR message to find out if there is a target ProSe UE interested in the service related to the source ProSe UE), but also initiate one or more Layer 2 link modification procedures towards the connected target UE. Based on this concept, the relay UE can send an LMR message to add the third source UE to the target UE. If the target UE accepts to reuse the second-hop PC5 link to communicate with the third source UE via the relay UE, the target UE can respond with an LMA message to the relay UE.

[0987] Alternatively, the relay UE may first complete (completely) the one or more link modification procedures toward the connected target UE, and then initiate a Layer 2 link establishment procedure (or broadcast a 2nd-hop DCR message) to find out whether any other target ProSe UE (which has not yet established a PC5 link with the relay UE) is also interested in communicating with the third source UE. In this way, since the third source UE has already been added to the 2nd-hop PC5 link using the link modification procedure toward the target UE, the target UE may ignore the received broadcast 2nd-hop DCR message.

[0988] Figure 22 FIG22 is a flow chart of a method for a relay UE. In step 2205, the relay UE establishes a PC5 connection with a target UE for communicating with a first source UE via the relay UE. In step 2210, the relay UE receives a first message from a second source UE to establish communication with any target ProSe UE. In step 2215, the relay UE initiates a link modification procedure toward the target UE in response to receiving the first message.

[0989] In one embodiment, the relay UE may initiate both a Layer 2 link establishment procedure and a link modification procedure toward the target UE in response to receiving the first message. In response to receiving the first message, the relay UE may initiate a Layer 2 link establishment procedure after the link modification procedure toward the target UE (and another link modification procedure toward any target UE connected to the relay UE) is completed. The Layer 2 link establishment procedure may be initiated toward an unspecified target ProSe UE.

[0990] In one embodiment, the first message may not include any user information of the target ProSe end UE.The first message may be a direct communication request message or a ProSe direct link establishment request message.

[0991] In one embodiment, the user information may be a user information ID or an application layer ID.

[0992] Return Reference Figure 3 and 4 In one example from the perspective of a relay UE, the relay UE 300 includes program code 312 stored in a memory 310. The CPU 308 can execute the program code 312 to enable the relay UE to: (i) establish a PC5 connection with a target UE for communicating with a first source UE via the relay UE; (ii) receive a first message from a second source UE to establish communication with any target ProSe UE; and (iii) initiate a link modification procedure toward the target UE in response to receiving the first message. In addition, the CPU 308 can execute the program code 312 to perform all of the above actions and steps or other actions and steps described herein.

[0993] Figure 23 2300 is a flowchart of a method for a target UE. In step 2305, the target UE receives a first message from a relay UE to establish a PC5 connection with the relay UE for communicating with a first source UE via the relay UE, wherein the PC5 connection is associated with first user information of the target UE. In step 2310, the target UE receives a second message from the relay UE to establish another PC5 connection with the relay UE for communicating with a second source UE via the relay UE. In step 2315, in response to receiving the second message, if the second message includes second user information belonging to or associated with the target UE, the target UE sends a third message to the relay UE.

[0994] In one embodiment, the target UE may receive a fourth message requesting modification of the PC5 connection from the relay UE, where the fourth message includes the second user information.

[0995] In one embodiment, the first message may include user information of the first source UE, user information of the relay UE, a relay service code, etc. The second message may include user information of the second source UE, user information of the relay UE, a relay service code, etc. The third message may include first user information, second user information, user information of the first source UE, user information of the second source UE, user information of the relay UE, a relay service code, a cause value, etc. The fourth message may include second user information, user information of the second source UE, a relay service code, etc.

[0996] In one embodiment, the first / second message may be a direct communication request message or a ProSe direct link establishment request message. The third message may be a direct communication reject message or a ProSe direct link establishment reject message. The fourth message may be a link modification request message or a ProSe direct link modification request message.

[0997] In one embodiment, the first / second source UE or target UE may be a 5G ProSe UE. The relay UE may be a 5G ProSe inter-UE relay UE. The cause value may indicate that the relay UE initiated a link modification procedure toward the target UE. The link modification procedure may be adding a second source UE to the PC5 connection. The user information may be a user information ID or an application layer ID.

[0998] Return Reference Figure 3 and 4 In one example from the perspective of a target UE, the target UE 300 includes program code 312 stored in a memory 310. The CPU 308 can execute the program code 312 to enable the target UE to: (i) receive a first message from the relay UE to establish a PC5 connection with the relay UE for communicating with a first source UE via the relay UE, wherein the PC5 connection is associated with first user information of the target UE; (ii) receive a second message from the relay UE to establish another PC5 connection with the relay UE for communicating with a second source UE via the relay UE; and (iii) in response to receiving the second message, send a third message to the relay UE if the second message includes second user information belonging to or associated with the target UE. In addition, the CPU 308 can execute the program code 312 to perform all of the above actions and steps or other actions and steps described herein.

[0999] Figure 242400 is a flowchart of a method for a relay UE. In step 2405, the relay UE establishes a PC5 connection with a target UE to support inter-UE relay communication between a first source UE and a target UE via the relay UE. In step 2410, the relay UE sends or broadcasts a first request message to the target UE requesting to establish another PC5 connection with the relay UE to support inter-UE relay communication with a second source UE via the relay UE. In step 2415, the relay UE receives a rejection message from the target UE, wherein the rejection message includes information instructing the relay UE to initiate a layer 2 link modification procedure on the PC5 connection. In step 2420, in response to receiving the rejection message, the relay UE sends a second request message to the target UE requesting to modify the PC5 connection.

[1000] In one embodiment, the first request message may include user information of the second source UE, user information of the relay UE, a relay service code, etc. The rejection message may include user information of the second source UE, user information of the target UE, user information of the relay UE, a cause value, etc. The second request message may include user information of the second source UE, user information of the target UE, etc.

[1001] In one embodiment, the first request message may be a direct communication request message or a ProSe direct link establishment request message, the rejection message may be a direct communication rejection message or a ProSe direct link establishment rejection message, and the second request message may be a link modification request message or a ProSe direct link modification request message.

[1002] Return Reference Figure 3 and 4 In one example from the perspective of a relay UE, the relay UE 300 includes program code 312 stored in a memory 310. The CPU 308 can execute the program code 312 to enable the relay UE to: (i) establish a PC5 connection with a target UE to support inter-UE relay communication between a first source UE and a target UE via the relay UE; (ii) send or broadcast a first request message to the target UE requesting to establish another PC5 connection with the relay UE to support inter-UE relay communication with a second source UE via the relay UE; (iii) receive a rejection message from the target UE, wherein the rejection message includes information instructing the relay UE to initiate a layer 2 link modification procedure on the PC5 connection; and (iv) in response to receiving the rejection message, send a second request message to the target UE requesting to modify the PC5 connection. In addition, the CPU 308 can execute the program code 312 to perform all of the above actions and steps or other actions and steps described herein.

[1003] Figure 252500 is a flow chart of a method for a target UE. In step 2505, the target UE establishes a PC5 connection with a relay UE to support inter-UE relay communication between a first source UE and a target UE via the relay UE. In step 2510, the target UE receives a request message from the relay UE requesting to establish another PC5 connection with the relay UE to support inter-UE relay communication with a second source UE via the relay UE. In step 2515, in response to receiving the request message, if the PC5 connection exists, the target UE sends a rejection message to the relay UE.

[1004] In one embodiment, the request message may include user information of the second source UE, user information of the relay UE, relay service code, etc. The rejection message may include user information of the second source UE, user information of the target UE, user information of the relay UE, reason value, etc.

[1005] In one embodiment, the request message may be a direct communication request message or a ProSe direct link setup request message, and the rejection message may be a direct communication rejection message or a ProSe direct link setup rejection message.

[1006] Return Reference Figure 3 and 4 In one example from the perspective of a target UE, the target UE 300 includes program code 312 stored in memory 310. The CPU 308 can execute the program code 312 to enable the target UE to: (i) establish a PC5 connection with the relay UE to support inter-UE relay communication between the first source UE and the target UE via the relay UE; (ii) receive a request message from the relay UE requesting to establish another PC5 connection with the relay UE to support inter-UE relay communication with the second source UE via the relay UE; and (iii) in response to receiving the request message, send a rejection message to the relay UE if the PC5 connection exists. In addition, the CPU 308 can execute the program code 312 to perform all of the above actions and steps or other actions and steps described herein.

[1007] Various aspects of the present disclosure have been described above. It should be understood that the teachings herein can be implemented in a wide variety of forms, and any specific structure, functionality, or both disclosed herein are merely representative. Based on the teachings herein, those skilled in the art will appreciate that the aspects disclosed herein can be implemented independently of any other aspects, and that two or more of these aspects can be combined in various ways. For example, a device or method can be implemented using any number of the aspects described herein. Furthermore, the device or method can be implemented using other structures, functionality, or structures and functionality in addition to or different from one or more of the aspects described herein. As an example of some of the above concepts, in some aspects, parallel channels can be established based on pulse repetition frequency. In some aspects, parallel channels can be established based on pulse position or offset. In some aspects, parallel channels can be established based on a time hopping sequence. In some aspects, parallel channels can be established based on pulse repetition frequency, pulse position or offset, and a time hopping sequence.

[1008] Those skilled in the art will understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[1009] Those skilled in the art will further appreciate that the various illustrative logical blocks, modules, processors, components, circuits, and algorithm steps described in connection with the various aspects disclosed herein can be implemented as electronic hardware (e.g., a digital implementation, an analog implementation, or a combination of the two, which can be designed using source decoding or some other technique), and various forms of programs or design code with instructions (which, for convenience, may be referred to herein as "software" or "software modules"), or a combination of the two. To clearly illustrate this interchangeability of hardware and software, the various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether this functionality is implemented as hardware or software depends on the specific application and the design constraints imposed on the overall system. Those skilled in the art may implement the described functionality in varying ways for each specific application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.

[1010] Furthermore, the various illustrative logical blocks, modules, and circuits described in connection with the aspects disclosed herein may be implemented within or performed by an integrated circuit ("IC"), an access terminal, or an access point. An IC may include a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, electrical components, optical components, mechanical components, or any combination thereof designed to perform the functions described herein, and may execute code or instructions residing within the IC, external to the IC, or both. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, for example, a combination of a DSP and a microprocessor, a combination of multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

[1011] It should be understood that any specific order or hierarchy of steps in any disclosed process is an example of a sample approach. It should be understood that based on design preferences, the specific order or hierarchy of steps in a process can be rearranged while remaining within the scope of the present disclosure. The accompanying method claims present elements of the various steps in a sample order and are not meant to be limited to the specific order or hierarchy presented.

[1012] The steps of the methods or algorithms described in conjunction with the various aspects disclosed herein can be implemented directly in hardware, in software modules executed by a processor, or in a combination of the two. Software modules (e.g., containing executable instructions and associated data) and other data can reside in a data memory, such as RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, removable disk, CD-ROM, or any other form of computer-readable storage medium known in the art. An example storage medium can be coupled to a machine such as a computer / processor (for convenience, the machine can be referred to herein as a "processor") so that the processor can read information (e.g., code) from the storage medium and write information to the storage medium. An example storage medium can be integrated with the processor. The processor and storage medium can reside in an ASIC. The ASIC can reside in a user device. In an alternative, the processor and storage medium can reside in a user device as discrete components. In addition, in some aspects, any suitable computer program product can include a computer-readable medium that includes code related to one or more of the various aspects of the present disclosure. In some aspects, the computer program product can include packaging materials.

[1013] Although the present invention has been described in conjunction with various aspects, it will be understood that the invention is capable of further modification. This application is intended to cover any variations, uses, or adaptations of the invention that generally follow the principles of the invention and include such deviations from the present disclosure as come within the scope of known and customary practice in the art to which the invention pertains.

[1014] CROSS-REFERENCE TO RELATED APPLICATIONS

[1015] This application claims the benefit of U.S. Provisional Patent Application Nos. 63 / 526,597 and 63 / 526,621, filed on July 13, 2023, the entire disclosures of which are incorporated herein by reference in their entirety.

Claims

1. A method for relaying user equipment, characterized in that: include: The relay user equipment establishes a PC5 connection with the target user equipment to support inter-user equipment relay communication between the first source user equipment and the target user equipment via the relay user equipment; The relay user equipment sends or broadcasts a first request message to the target user equipment requesting to establish another PC5 connection with the relay user equipment to support relay communication between user equipments via the relay user equipment and the second source user equipment; The relay user equipment receives a rejection message from the target user equipment, wherein the rejection message includes information instructing the relay user equipment to initiate a layer 2 link modification procedure on the PC5 connection; as well as In response to receiving the rejection message, the relay user equipment sends a second request message to the target user equipment requesting to modify the connection of PC5.

2. The method according to claim 1, characterized in that The first request message includes user information of the second source user equipment, user information of the relay user equipment and / or a relay service code.

3. The method according to claim 2, characterized in that The rejection message includes the user information of the second source user equipment, the user information of the target user equipment, the user information of the relay user equipment and / or a reason value.

4. The method according to claim 3, characterized in that The second request message includes the user information of the second source-end user equipment and / or the user information of the target-end user equipment.

5. The method according to claim 1, characterized in that The first request message is a direct communication request message or a proximity based service direct link establishment request message, the rejection message is a direct communication rejection message or a proximity based service direct link establishment rejection message, and the second request message is a link modification request message or a proximity based service direct link modification request message.

6. A method for a target end user device, characterized in that: include: The target user equipment establishes a PC5 connection with the relay user equipment to support the inter-user equipment relay communication between the first source user equipment and the target user equipment via the relay user equipment; The target user equipment receives a request message from the relay user equipment requesting to establish another PC5 connection with the relay user equipment to support relay communication between user equipments with the second source user equipment via the relay user equipment; as well as In response to receiving the request message, if the PC5 connection exists, the target user equipment sends a rejection message to the relay user equipment.

7. The method according to claim 6, characterized in that The request message includes user information of the second source user equipment, user information of the relay user equipment and / or a relay service code.

8. The method according to claim 7, characterized in that The rejection message includes the user information of the second source user equipment, the user information of the target user equipment, the user information of the relay user equipment and / or a reason value.

9. The method according to claim 6, characterized in that The request message is a direct communication request message or a proximity based service direct link establishment request message, and the rejection message is a direct communication rejection message or a proximity based service direct link establishment rejection message.

10. A target end user equipment, characterized in that: include: Control circuit; a processor installed in the control circuit; as well as a memory installed in the control circuit and operatively coupled to the processor; The processor is configured to execute the program code stored in the memory to perform the following operations: Establishing a PC5 connection with a relay user device to support inter-user device relay communication between the first source user device and the target user device via the relay user device; receiving, from the relay user equipment, a request message for establishing another PC5 connection with the relay user equipment to support relay communication between user equipments via the relay user equipment and a second source user equipment; as well as In response to receiving the request message, if the PC5 connection exists, a rejection message is sent to the relay user equipment.

11. The target end user equipment according to claim 10, characterized in that: The request message includes user information of the second source user equipment, user information of the relay user equipment and / or a relay service code.

12. The target end user equipment according to claim 11, characterized in that: The rejection message includes the user information of the second source user equipment, the user information of the target user equipment, the user information of the relay user equipment and / or a reason value.

13. The target end user equipment according to claim 10, characterized in that: The request message is a direct communication request message or a proximity based service direct link establishment request message, and the rejection message is a direct communication rejection message or a proximity based service direct link establishment rejection message.

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