Methods for multi-hop wtru-to-network relay discovery using relay discovery set with hop count

Abstract

A wireless transmit / receive unit (WTRU) may receive a request from a remote WTRU to establish a multi-hop WTRU-to-network connection between the remote WTRU and a network relay WTRU. The WTRU may send a first security mode command message to the remote WTRU to establish secure communications with the remote WTRU over a direct sidelink interface between the WTRU and the remote WTRU. The WTRU may receive a first security mode complete message from the remote WTRU. The WTRU may send a communication request message to the network relay WTRU. The WTRU may receive a second security mode command message from the network relay WTRU. The WTRU may determine a key new radio ProSe (KNRP) based on the PRK to authorize the remote WTRU and / or network relay WTRU for the multi-hop network relay WTRU connection. The WTRU may send a second security mode complete message to the network relay WTRU.

Description

METHODS FOR MULTI-HOP WTRU-TO-NETWORK RELAY DISCOVERY USING RELAY DISCOVERY SET WITH HOP COUNTCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 517,403 filed on August 3, 2023, the entire contents of which are incorporated herein by reference.BACKGROUND

[0002] A wireless transmit / receive unit (WTRU) to network (U2N) Relay discovery and / or communication security may be implemented as described herein. The Third Generation Partnership Project (3GPP) has defined U2N procedures for discovery and / or communication, including security and / or privacy. U2N Relay direct discovery using Model A or B may be supported. In Model A, the U2N Relay may send announcement discovery messages to be received by Remote WTRUs in proximity. In Model B, the Remote WTRU may send solicitation discovery messages to which discoverable U2N Relays reply with a corresponding response message.

[0003] Discovery security parameters (e.g., keys and / or timing information) associated with a U2N Relay service code (RSC) may be provisioned in the Remote WTRU and / or U2N Relay. The U2N may protect discovery messages and / or some sensitive parameters in a direct connection request (DCR) message (e.g., RSC). A direct discovery name management function (DDNMF), a policy control function (PCF), and / or a ProSe key management function (PKMF) may provide the remote WTRU relay with security parameters.

[0004] U2N Relay direct communication may support two alternative user plane (UP) and / or control plane (CP) based security mechanisms. In these security mechanisms, a root credential called ProSe remote user key (PRUK) may be respectively provisioned and / or generated.

[0005] In the CP based security mechanism, the Remote WTRU may establish the root credential (CP-PRUK) with Remote WTRU home public land mobile network (HPLMN) (e.g., authentication server function (AUSF), unified data management (UDM), and / or ProSe anchor function (PAnF)) during a ProSe authentication procedure as part of PC5link establishment with the U2N Relay. This authentication requires the 3GPP credential stored in the Remote WTRU universal integrated circuit card (UICC).

[0006] In the UP based security mechanism, the PKMF may configure the Remote WTRU with the root credential user plane ProSe key management Function (UP- PRUK). The UP-PRUK may also be generated as part of PC5 link establishment with the U2N Relay using a generic bootstrapping architecture (GBA-PUSH) mechanism. The GBA-PUSH mechanism similarly may require the 3GPP credential stored in the Remote UE UICC.

[0007] The PRUK may establish a PC5 link root key KNRP shared between the Remote WTRU and U2N Relay. The PRUK may be used to establish and / or used to derive session and / or security keys. The Remote WTRU derives KNRP from PRUK, while the U2N Relay receives KNRP from the network (e.g., PKMF and / or AMF).SUMMARY

[0008] A wireless transmit / receive unit (WTRU) may receive a request from a remote WTRU to establish a multi-hop WTRU-to-network (U2N) connection between the remote WTRU and a network relay WTRU. The WTRU may send a first security mode command message to the remote WTRU to establish secure communications with the remote WTRU over a direct sidelink interface between the WTRU and the remote WTRU. The WTRU may receive a first security mode complete message from the remote WTRU. The first security mode complete message may comprise a ProSe relay key (PRK) and a noncel . The PRK may be based on a user plane ProSe remote user key (UP-PRUK) of the remote WTRU. The WTRU may send a communication request message to the network relay WTRU. The WTRU may receive a second security mode command message from the network relay WTRU. The WTRU may determine a key new radio ProSe (KNRP) based at least on the PRK to authorize the remote WTRU and network relay WTRU for the multi-hop network relay WTRU connection. The WTRU may send a second security mode complete message to the network relay WTRU. The WTRU may send an accept message to the remote WTRU.

[0009] The request may comprise a relay service code (RSC) associated with the WTRU, an RSC associated with the network relay WTRU, and / or an UP-PRUK ID. The WTRUmay receive discovery and / or communication parameters from a direct discovery name management function (DDNMF), policy control function (PCF), and / or a ProSe key management function (PKMF). The discovery and / or communication parameters may comprise a multi-hop support indicator for establishing multi-hop connections.

[0010] The WTRLI may perform mutual authentication with the remote WTRU using a long term credential (LTC). The WTRU may perform mutual authentication with the remote WTRU prior to sending the security mode message.

[0011] The communication request message may comprise one or more of a relay service code (RSC) associated with the network relay WTRU, a nonce2, and / or a first UP-PRUK ID. The communication request message may further comprise one or more of a second UP-PRUK ID. The second UP-PRUK ID may be associated with the network relay WTRU. The second UP-PRUK ID may establish the multi-hop U2N connection without network assistance.

[0012] The WTRU may receive the accept message from the network relay WTRU prior to sending the accept message to the remote WTRU. The PRK may be further based on a relay service code (RSC) associated with the WTRU and / or a control plane ProSe remote user key (CP-PRUK) of the remote WTRU.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1A is a system diagram illustrating an example communications system in which one or more disclosed embodiments may be implemented.

[0014] FIG. 1 B is a system diagram illustrating an example wireless transmit / receive unit (WTRU) that may be used within the communications system illustrated in FIG. 1A according to an embodiment.

[0015] FIG. 1 C is a system diagram illustrating an example radio access network (RAN) and an example core network (CN) that may be used within the communications system illustrated in FIG. 1A according to an embodiment.

[0016] FIG. 1 D is a system diagram illustrating a further example RAN and a further example CN that may be used within the communications system illustrated in FIG. 1A according to an embodiment.

[0017] FIG. 2 is a block diagram illustrating a PC5 key hierarchy for 5G ProSe wireless transmit / receive unit (WTRU) to network (U2N) Relay security over the user plane (UP).

[0018] FIG. 3 is a block diagram illustrating an example Model A based WTRU-to- WTRU (U2U) Relay discovery for U2N Relay using hope count based selection and / or filtering.

[0019] FIG. 4 is a block diagram illustrating an example PC5 key hierarchy for 5G ProSe U2N Relay security over the UP enhancements for multi-hop support.

[0020] FIGs. 5A-5B are flow diagrams illustrating example PC5 security establishment procedures for 5G ProSe (U2N) Relay communication over UP with enhancements for multi-hop.

[0021] FIG. 6 is a block diagram illustrating an example PC5 key hierarchy for 5G ProSe U2N Relay security over the UP enhancements with a dedicated multi-hop root credential.

[0022] FIGs. 7A-7B are flow diagrams illustrating example PC5 security establishment procedures for multi-hop 5G U2N Relay communications over UP with enhancements for multi-hop.DETAILED DESCRIPTION

[0023] FIG. 1A is a diagram illustrating an example communications system 100 in which one or more disclosed embodiments may be implemented. The communications system 100 may be a multiple access system that provides content, such as voice, data, video, messaging, broadcast, etc., to multiple wireless users. The communications system 100 may enable multiple wireless users to access such content through the sharing of system resources, including wireless bandwidth. For example, the communications systems 100 may employ one or more channel access methods, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrier FDMA (SC-FDMA), zero-tail unique-word DFT-Spread OFDM (ZT UW DTS-s OFDM), unique word OFDM (UW-OFDM), resource block-filtered OFDM, filter bank multicarrier (FBMC), and the like.

[0024] As shown in FIG. 1A, the communications system 100 may include wireless transmit / receive units (WTRUs) 102a, 102b, 102c, 102d, a RAN 104 / 113, a CN 106 / 115, a public switched telephone network (PSTN) 108, the Internet 110, and other networks 112, though it will be appreciated that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and / or network elements. Each of the WTRUs 102a, 102b, 102c, 102d may be any type of device configured to operate and / or communicate in a wireless environment. By way of example, the WTRUs 102a, 102b, 102c, 102d, any of which may be referred to as a “station” and / or a “STA,” may be configured to transmit and / or receive wireless signals and may include a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a subscriptionbased unit, a pager, a cellular telephone, a personal digital assistant (PDA), a smartphone, a laptop, a netbook, a personal computer, a wireless sensor, a hotspot or Mi-Fi device, an Internet of Things (loT) device, a watch or other wearable, a headmounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and / or other wireless devices operating in an industrial and / or an automated processing chain contexts), a consumer electronics device, a device operating on commercial and / or industrial wireless networks, and the like. Any of the WTRUs 102a, 102b, 102c, 102d may be interchangeably referred to as a WTRU.

[0025] The communications systems 100 may also include a base station 114a and / or a base station 114b. Each of the base stations 114a, 114b may be any type of device configured to wirelessly interface with at least one of the WTRUs 102a, 102b, 102c, 102d to facilitate access to one or more communication networks, such as the CN 106 / 115, the Internet 110, and / or the other networks 112. By way of example, the base stations 114a, 114b may be a base transceiver station (BTS), a Node-B, an eNode B, a Home Node B, a Home eNode B, a gNB, a NR NodeB, a site controller, an access point (AP), a wireless router, and the like. While the base stations 114a, 114b are each depicted as a single element, it will be appreciated that the base stations 114a, 114b may include any number of interconnected base stations and / or network elements.

[0026] The base station 114a may be part of the RAN 104 / 113, which may also include other base stations and / or network elements (not shown), such as a base stationcontroller (BSC), a radio network controller (RNC), relay nodes, etc. The base station 114a and / or the base station 11 b may be configured to transmit and / or receive wireless signals on one or more carrier frequencies, which may be referred to as a cell (not shown). These frequencies may be in licensed spectrum, unlicensed spectrum, or a combination of licensed and unlicensed spectrum. A cell may provide coverage for a wireless service to a specific geographical area that may be relatively fixed, or that may change over time. The cell may further be divided into cell sectors. For example, the cell associated with the base station 114a may be divided into three sectors. Thus, in one embodiment, the base station 114a may include three transceivers, i.e. , one for each sector of the cell. In an embodiment, the base station 114a may employ multiple-input multiple output (MIMO) technology and may utilize multiple transceivers for each sector of the cell. For example, beamforming may be used to transmit and / or receive signals in desired spatial directions.

[0027] The base stations 114a, 114b may communicate with one or more of the WTRUs 102a, 102b, 102c, 102d over an air interface 116, which may be any suitable wireless communication link (e.g., radio frequency (RF), microwave, centimeter wave, micrometer wave, infrared (IR), ultraviolet (UV), visible light, etc.). The air interface 116 may be established using any suitable radio access technology (RAT).

[0028] More specifically, as noted above, the communications system 100 may be a multiple access system and may employ one or more channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. For example, the base station 114a in the RAN 104 / 113 and the WTRUs 102a, 102b, 102c may implement a radio technology such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which may establish the air interface 115 / 116 / 117 using wideband CDMA (WCDMA). WCDMA may include communication protocols such as High-Speed Packet Access (HSPA) and / or Evolved HSPA (HSPA+). HSPA may include High-Speed Downlink (DL) Packet Access (HSDPA) and / or High-Speed UL Packet Access (HSUPA).

[0029] In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as Evolved UMTS Terrestrial Radio Access (E-UTRA), which may establish the air interface 116 using Long Term Evolution (LTE) and / or LTE-Advanced (LTE-A) and / or LTE-Advanced Pro (LTE -A Pro).

[0030] In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as NR Radio Access, which may establish the air interface 116 using New Radio (NR).

[0031] In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement multiple radio access technologies. For example, the base station 114a and the WTRUs 102a, 102b, 102c may implement LTE radio access and NR radio access together, for instance, using dual connectivity (DC) principles. Thus, the air interface utilized by WTRUs 102a, 102b, 102c may be characterized by multiple types of radio access technologies and / or transmissions sent to / from multiple types of base stations (e.g., a eNB and a gNB).

[0032] In other embodiments, the base station 114a and the WTRUs 102a, 102b, 102c may implement radio technologies such as IEEE 802.11 (i.e., Wireless Fidelity (WiFi), IEEE 802.16 (i.e., Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 1X, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), Interim Standard 856 (IS-856), Global System for Mobile communications (GSM), Enhanced Data rates for GSM Evolution (EDGE), GSM EDGE (GERAN), and the like.

[0033] The base station 114b in FIG. 1A may be a wireless router, Home Node B, Home eNode B, or access point, for example, and may utilize any suitable RAT for facilitating wireless connectivity in a localized area, such as a place of business, a home, a vehicle, a campus, an industrial facility, an air corridor (e.g., for use by drones), a roadway, and the like. In one embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.11 to establish a wireless local area network (WLAN). In an embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.15 to establish a wireless personal area network (WPAN). In yet another embodiment, the base station 114b and the WTRUs 102c, 102d may utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, LTE-A Pro, NR, etc.) to establish a picocell or femtocell. As shown in FIG. 1 A, the base station 114b may have a direct connection tothe Internet 110. Thus, the base station 114b may not be required to access the Internet 110 via the CN 106 / 115.

[0034] The RAN 104 / 113 may be in communication with the CN 106 / 115, which may be any type of network configured to provide voice, data, applications, and / or voice over internet protocol (VoIP) services to one or more of the WTRUs 102a, 102b, 102c, 102d. The data may have varying quality of service (QoS) requirements, such as differing throughput requirements, latency requirements, error tolerance requirements, reliability requirements, data throughput requirements, mobility requirements, and the like. The CN 106 / 115 may provide call control, billing services, mobile location-based services, pre-paid calling, Internet connectivity, video distribution, etc., and / or perform high-level security functions, such as user authentication. Although not shown in FIG. 1A, it will be appreciated that the RAN 104 / 113 and / or the CN 106 / 115 may be in direct or indirect communication with other RANs that employ the same RAT as the RAN 104 / 113 or a different RAT. For example, in addition to being connected to the RAN 104 / 113, which may be utilizing a NR radio technology, the CN 106 / 115 may also be in communication with another RAN (not shown) employing a GSM, UMTS, CDMA 2000, WiMAX, E- UTRA, or WiFi radio technology.

[0035] The CN 106 / 115 may also serve as a gateway for the WTRUs 102a, 102b, 102c, 102d to access the PSTN 108, the Internet 110, and / or the other networks 112. The PSTN 108 may include circuit-switched telephone networks that provide plain old telephone service (POTS). The Internet 110 may include a global system of interconnected computer networks and devices that use common communication protocols, such as the transmission control protocol (TCP), user datagram protocol (UDP) and / or the internet protocol (IP) in the TCP / IP internet protocol suite. The networks 112 may include wired and / or wireless communications networks owned and / or operated by other service providers. For example, the networks 112 may include another CN connected to one or more RANs, which may employ the same RAT as the RAN 104 / 113 or a different RAT.

[0036] Some or all of the WTRUs 102a, 102b, 102c, 102d in the communications system 100 may include multi-mode capabilities (e.g., the WTRUs 102a, 102b, 102c, 102d may include multiple transceivers for communicating with different wirelessnetworks over different wireless links). For example, the WTRU 102c shown in FIG. 1 A may be configured to communicate with the base station 114a, which may employ a cellular-based radio technology, and with the base station 114b, which may employ an IEEE 802 radio technology.

[0037] FIG. 1 B is a system diagram illustrating an example WTRU 102. As shown in FIG. 1 B, the WTRU 102 may include a processor 118, a transceiver 120, a transmit / receive element 122, a speaker / microphone 124, a keypad 126, a display / touchpad 128, non-removable memory 130, removable memory 132, a power source 134, a global positioning system (GPS) chipset 136, and / or other peripherals 138, among others. It will be appreciated that the WTRU 102 may include any subcombination of the foregoing elements while remaining consistent with an embodiment.

[0038] The processor 118 may be a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) circuits, any other type of integrated circuit (IC), a state machine, and the like. The processor 118 may perform signal coding, data processing, power control, input / output processing, and / or any other functionality that enables the WTRU 102 to operate in a wireless environment. The processor 118 may be coupled to the transceiver 120, which may be coupled to the transmit / receive element 122. While FIG. 1 B depicts the processor 118 and the transceiver 120 as separate components, it will be appreciated that the processor 118 and the transceiver 120 may be integrated together in an electronic package or chip.

[0039] The transmit / receive element 122 may be configured to transmit signals to or receive signals from a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, the transmit / receive element 122 may be an antenna configured to transmit and / or receive RF signals. In an embodiment, the transmit / receive element 122 may be an emitter / detector configured to transmit and / or receive IR, UV, or visible light signals, for example. In yet another embodiment, the transmit / receive element 122 may be configured to transmit and / or receive both RF andlight signals. It will be appreciated that the transmit / receive element 122 may be configured to transmit and / or receive any combination of wireless signals.

[0040] Although the transmit / receive element 122 is depicted in FIG. 1 B as a single element, the WTRU 102 may include any number of transmit / receive elements 122. More specifically, the WTRU 102 may employ MIMO technology. Thus, in one embodiment, the WTRU 102 may include two or more transmit / receive elements 122 (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface 116.

[0041] The transceiver 120 may be configured to modulate the signals that are to be transmitted by the transmit / receive element 122 and to demodulate the signals that are received by the transmit / receive element 122. As noted above, the WTRU 102 may have multi-mode capabilities. Thus, the transceiver 120 may include multiple transceivers for enabling the WTRU 102 to communicate via multiple RATs, such as NR and IEEE 802.11 , for example.

[0042] The processor 118 of the WTRU 102 may be coupled to, and may receive user input data from, the speaker / microphone 124, the keypad 126, and / or the display / touchpad 128 (e.g., a liquid crystal display (LCD) display unit or organic lightemitting diode (OLED) display unit). The processor 118 may also output user data to the speaker / microphone 124, the keypad 126, and / or the display / touchpad 128. In addition, the processor 118 may access information from, and store data in, any type of suitable memory, such as the non-removable memory 130 and / or the removable memory 132. The non-removable memory 130 may include random-access memory (RAM), readonly memory (ROM), a hard disk, or any other type of memory storage device. The removable memory 132 may include a subscriber identity module (SIM) card, a memory stick, a secure digital (SD) memory card, and the like. In other embodiments, the processor 118 may access information from, and store data in, memory that is not physically located on the WTRU 102, such as on a server or a home computer (not shown).

[0043] The processor 118 may receive power from the power source 134 and may be configured to distribute and / or control the power to the other components in the WTRU 102. The power source 134 may be any suitable device for powering the WTRU 102.For example, the power source 134 may include one or more dry cell batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li- ion), etc.), solar cells, fuel cells, and the like.

[0044] The processor 118 may also be coupled to the GPS chipset 136, which may be configured to provide location information (e.g., longitude and latitude) regarding the current location of the WTRU 102. In addition to, or in lieu of, the information from the GPS chipset 136, the WTRU 102 may receive location information over the air interface 116 from a base station (e.g., base stations 114a, 114b) and / or determine its location based on the timing of the signals being received from two or more nearby base stations. It will be appreciated that the WTRU 102 may acquire location information by way of any suitable location-determination method while remaining consistent with an embodiment.

[0045] The processor 118 may further be coupled to other peripherals 138, which may include one or more software and / or hardware modules that provide additional features, functionality and / or wired or wireless connectivity. For example, the peripherals 138 may include an accelerometer, an e-compass, a satellite transceiver, a digital camera (for photographs and / or video), a universal serial bus (USB) port, a vibration device, a television transceiver, a hands free headset, a Bluetooth® module, a frequency modulated (FM) radio unit, a digital music player, a media player, a video game player module, an Internet browser, a Virtual Reality and / or Augmented Reality (VR / AR) device, an activity tracker, and the like. The peripherals 138 may include one or more sensors, the sensors may be one or more of a gyroscope, an accelerometer, a hall effect sensor, a magnetometer, an orientation sensor, a proximity sensor, a temperature sensor, a time sensor, a geolocation sensor, an altimeter, a light sensor, a touch sensor, a magnetometer, a barometer, a gesture sensor, a biometric sensor, and / or a humidity sensor.

[0046] The WTRU 102 may include a full duplex radio for which transmission and reception of some or all of the signals (e.g., associated with particular subframes for both the UL (e.g., for transmission) and downlink (e.g., for reception) may be concurrent and / or simultaneous. The full duplex radio may include an interference management unit 139 to reduce and or substantially eliminate self-interference via either hardware(e.g., a choke) or signal processing via a processor (e.g., a separate processor (not shown) or via processor 118). In an embodiment, the WRTU 102 may include a halfduplex radio for which transmission and reception of some or all of the signals (e.g., associated with particular subframes for either the LIL (e.g., for transmission) or the downlink (e.g., for reception)).

[0047] FIG. 1 C is a system diagram illustrating the RAN 104 and the CN 106 according to an embodiment. As noted above, the RAN 104 may employ an E-UTRA radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 104 may also be in communication with the CN 106.

[0048] The RAN 104 may include eNode-Bs 160a, 160b, 160c, though it will be appreciated that the RAN 104 may include any number of eNode-Bs while remaining consistent with an embodiment. The eNode-Bs 160a, 160b, 160c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In one embodiment, the eNode-Bs 160a, 160b, 160c may implement MIMO technology. Thus, the eNode-B 160a, for example, may use multiple antennas to transmit wireless signals to, and / or receive wireless signals from, the WTRU 102a.

[0049] Each of the eNode-Bs 160a, 160b, 160c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in the UL and / or DL, and the like. As shown in FIG. 1 C, the eNode-Bs 160a, 160b, 160c may communicate with one another over an X2 interface.

[0050] The CN 106 shown in FIG. 1 C may include a mobility management entity (MME) 162, a serving gateway (SGW) 164, and a packet data network (PDN) gateway (or PGW) 166. While each of the foregoing elements is depicted as part of the CN 106, it will be appreciated that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0051] The MME 162 may be connected to each of the eNode-Bs 162a, 162b, 162c in the RAN 104 via an S1 interface and may serve as a control node. For example, the MME 162 may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, bearer activation / deactivation, selecting a particular serving gateway during an initial attachment of the WTRUs 102a, 102b, 102c, and the like. The MME 162 may provide acontrol plane function for switching between the RAN 104 and other RANs (not shown) that employ other radio technologies, such as GSM and / or WCDMA.

[0052] The SGW 164 may be connected to each of the eNode Bs 160a, 160b, 160c in the RAN 104 via the S1 interface. The SGW 164 may generally route and forward user data packets to / from the WTRUs 102a, 102b, 102c. The SGW 164 may perform other functions, such as anchoring user planes during inter-eNode B handovers, triggering paging when DL data is available for the WTRUs 102a, 102b, 102c, managing and storing contexts of the WTRUs 102a, 102b, 102c, and the like.

[0053] The SGW 164 may be connected to the PGW 166, which may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c, and IP-enabled devices.

[0054] The ON 106 may facilitate communications with other networks. For example, the ON 106 may provide the WTRUs 102a, 102b, 102c with access to circuit-switched networks, such as the PSTN 108, to facilitate communications between the WTRUs 102a, 102b, 102c, and traditional land-line communications devices. For example, the CN 106 may include or may communicate with, an IP gateway (e.g., an IP multimedia subsystem (IMS) server) that serves as an interface between the CN 106 and the PSTN 108. In addition, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to the other networks 112, which may include other wired and / or wireless networks that are owned and / or operated by other service providers.

[0055] Although the WTRU is described in FIGs. 1A-1 D as a wireless terminal, it is contemplated that in certain representative embodiments that such a terminal may use (e.g., temporarily or permanently) wired communication interfaces with the communication network.

[0056] In representative embodiments, the other network 112 may be a WLAN.

[0057] A WLAN in Infrastructure Basic Service Set (BSS) mode may have an Access Point (AP) for the BSS and one or more stations (STAs) associated with the AP. The AP may have an access or an interface to a Distribution System (DS) or another type of wired / wireless network that carries traffic in to and / or out of the BSS. Traffic to STAs that originates from outside the BSS may arrive through the AP and may be delivered tothe STAs. Traffic originating from STAs to destinations outside the BSS may be sent to the AP to be delivered to respective destinations. Traffic between STAs within the BSS may be sent through the AP, for example, where the source STA may send traffic to the AP and the AP may deliver the traffic to the destination STA. The traffic between STAs within a BSS may be considered and / or referred to as peer-to-peer traffic. The peer-to- peer traffic may be sent between (e.g., directly between) the source and destination STAs with a direct link setup (DLS). In certain representative embodiments, the DLS may use an 802.11 e DLS or an 802.11 z tunneled DLS (TDLS). A WLAN using an Independent BSS (IBSS) mode may not have an AP, and the STAs (e.g., all of the STAs) within or using the IBSS may communicate directly with each other. The IBSS mode of communication may sometimes be referred to herein as an “ad-hoc” mode of communication.

[0058] When using the 802.11ac infrastructure mode of operation or a similar mode of operation, the AP may transmit a beacon on a fixed channel, such as a primary channel. The primary channel may be a fixed width (e.g., 20 MHz wide bandwidth) or a dynamically set width via signaling. The primary channel may be the operating channel of the BSS and may be used by the STAs to establish a connection with the AP. In certain representative embodiments, Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA) may be implemented, for example, in 802.11 systems. For CSMA / CA, the STAs (e.g., every STA), including the AP, may sense the primary channel. If the primary channel is sensed / detected and / or determined to be busy by a particular STA, the particular STA may back off. One STA (e.g., only one station) may transmit at any given time in a given BSS.

[0059] High Throughput (HT) STAs may use a 40 MHz wide channel for communication, for example, via a combination of the primary 20 MHz channel with an adjacent or nonadjacent 20 MHz channel to form a 40 MHz wide channel.

[0060] Very High Throughput (VHT) STAs may support 20MHz, 40 MHz, 80 MHz, and / or 160 MHz wide channels. The 40 MHz, and / or 80 MHz, channels may be formed by combining contiguous 20 MHz channels. A 160 MHz channel may be formed by combining 8 contiguous 20 MHz channels or by combining two non-contiguous 80 MHz channels, which may be referred to as an 80+80 configuration. For the 80+80configuration, the data, after channel encoding, may be passed through a segment parser that may divide the data into two streams. Inverse Fast Fourier Transform (IFFT) processing, and time domain processing, may be done on each stream separately. The streams may be mapped on to the two 80 MHz channels, and the data may be transmitted by a transmitting STA. At the receiver of the receiving STA, the above described operation for the 80+80 configuration may be reversed, and the combined data may be sent to the Medium Access Control (MAC).

[0061] Sub 1 GHz modes of operation are supported by 802.11 af and 802.11 ah. The channel operating bandwidths, and carriers, are reduced in 802.11af and 802.11 ah relative to those used in 802.11 n and 802.11 ac. 802.11 af supports 5 MHz, 10 MHz, and 20 MHz bandwidths in the TV White Space (TVWS) spectrum, and 802.11 ah supports 1 MHz, 2 MHz, 4 MHz, 8 MHz, and 16 MHz bandwidths using non-TVWS spectrum. According to a representative embodiment, 802.11 ah may support Meter Type Control / Machine-Type Communications, such as MTC devices in a macro coverage area. MTC devices may have certain capabilities, for example, limited capabilities, including support for (e.g., only support for) certain and / or limited bandwidths. The MTC devices may include a battery with a battery life above a threshold (e.g., to maintain a very long battery life).

[0062] WLAN systems, which may support multiple channels and channel bandwidths, such as 802.11 n, 802.11 ac, 802.11 af, and 802.11 ah, include a channel which may be designated as the primary channel. The primary channel may have a bandwidth equal to the largest common operating bandwidth supported by all STAs in the BSS. The bandwidth of the primary channel may be set and / or limited by a STA, from among all STAs in operating in a BSS, which supports the smallest bandwidth operating mode. In the example of 802.11 ah, the primary channel may be 1 MHz wide for STAs (e.g., MTC type devices) that support (e.g., only support) a 1 MHz mode, even if the AP, and other STAs in the BSS support 2 MHz, 4 MHz, 8 MHz, 16 MHz, and / or other channel bandwidth operating modes. Carrier sensing and / or Network Allocation Vector (NAV) settings may depend on the status of the primary channel. If the primary channel is busy, for example, due to a STA (which supports only a 1 MHz operating mode),transmitting to the AP, the entire available frequency bands may be considered busy even though a majority of the frequency bands remain idle and may be available.

[0063] In the United States, the available frequency bands, which may be used by 802.11 ah, are from 902 MHz to 928 MHz. In Korea, the available frequency bands are from 917.5 MHz to 923.5 MHz. In Japan, the available frequency bands are from 916.5 MHz to 927.5 MHz. The total bandwidth available for 802.11 ah is 6 MHz to 26 MHz depending on the country code.

[0064] FIG. 1 D is a system diagram illustrating the RAN 113 and the CN 115 according to an embodiment. As noted above, the RAN 113 may employ an NR radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 113 may also be in communication with the CN 115.

[0065] The RAN 113 may include gNBs 180a, 180b, 180c, though it will be appreciated that the RAN 113 may include any number of gNBs while remaining consistent with an embodiment. The gNBs 180a, 180b, 180c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In one embodiment, the gNBs 180a, 180b, 180c may implement MIMO technology. For example, gNBs 180a, 108b may utilize beamforming to transmit signals to and / or receive signals from the gNBs 180a, 180b, 180c. Thus, the gNB 180a, for example, may use multiple antennas to transmit wireless signals to, and / or receive wireless signals from, the WTRU 102a. In an embodiment, the gNBs 180a, 180b, 180c may implement carrier aggregation technology. For example, the gNB 180a may transmit multiple component carriers to the WTRU 102a (not shown). A subset of these component carriers may be on unlicensed spectrum, while the remaining component carriers may be on licensed spectrum. In an embodiment, the gNBs 180a, 180b, 180c may implement Coordinated Multi-Point (CoMP) technology. For example, WTRU 102a may receive coordinated transmissions from gNB 180a and gNB 180b (and / or gNB 180c).

[0066] The WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c using transmissions associated with a scalable numerology. For example, the OFDM symbol spacing and / or OFDM subcarrier spacing may vary for different transmissions, different cells, and / or different portions of the wireless transmission spectrum. The WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c usingsubframe or transmission time intervals (TTIs) of various or scalable lengths (e.g., containing varying numbers of OFDM symbols and / or lasting varying lengths of absolute time).

[0067] The gNBs 180a, 180b, 180c may be configured to communicate with the WTRUs 102a, 102b, 102c in a standalone configuration and / or a non-standalone configuration. In the standalone configuration, WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c without also accessing other RANs (e.g., such as eNode-Bs 160a, 160b, 160c). In the standalone configuration, WTRUs 102a, 102b, 102c may utilize one or more of gNBs 180a, 180b, 180c as a mobility anchor point. In the standalone configuration, WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c using signals in an unlicensed band. In a non-standalone configuration WTRUs 102a, 102b, 102c may communicate with / connect to gNBs 180a, 180b, 180c while also communicating with / connecting to another RAN such as eNode-Bs 160a, 160b, 160c. For example, WTRUs 102a, 102b, 102c may implement DC principles to communicate with one or more gNBs 180a, 180b, 180c, and one or more eNode-Bs 160a, 160b, 160c substantially simultaneously. In the non-standalone configuration, eNode-Bs 160a, 160b, 160c may serve as a mobility anchor for WTRUs 102a, 102b, 102c, and gNBs 180a, 180b, 180c may provide additional coverage and / or throughput for servicing WTRUs 102a, 102b, 102c.

[0068] Each of the gNBs 180a, 180b, 180c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in the UL and / or DL, support of network slicing, dual connectivity, interworking between NR and E-UTRA, routing of user plane data towards User Plane Function (UPF) 184a, 184b, routing of control plane information towards Access and Mobility Management Function (AMF) 182a, 182b and the like. As shown in FIG. 1 D, the gNBs 180a, 180b, 180c may communicate with one another over an Xn interface.

[0069] The CN 115 shown in FIG. 1 D may include at least one AMF 182a, 182b, at least one UPF 184a, 184b, at least one Session Management Function (SMF) 183a, 183b, and possibly a Data Network (DN) 185a, 185b. While each of the foregoingelements are depicted as part of the CN 115, it will be appreciated that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0070] The AMF 182a, 182b may be connected to one or more of the gNBs 180a, 180b, 180c in the RAN 113 via an N2 interface and may serve as a control node. For example, the AMF 182a, 182b may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, support for network slicing (e.g., handling of different PDU sessions with different requirements), selecting a particular SMF 183a, 183b, management of the registration area, termination of NAS signaling, mobility management, and the like. Network slicing may be used by the AMF 182a, 182b in order to customize CN support for WTRUs 102a, 102b, 102c based on the types of services being utilized WTRUs 102a, 102b, 102c. For example, different network slices may be established for different use cases, such as services relying on ultra-reliable low latency (URLLC) access, services relying on enhanced massive mobile broadband (eMBB) access, services for machine type communication (MTC) access, and / or the like. The AMF 162 may provide a control plane function for switching between the RAN 113 and other RANs (not shown) that employ other radio technologies, such as LTE, LTE-A, LTE-A Pro, and / or non-3GPP access technologies such as WiFi.

[0071] The SMF 183a, 183b may be connected to an AMF 182a, 182b in the CN 115 via an N11 interface. The SMF 183a, 183b may also be connected to a UPF 184a, 184b in the CN 115 via an N4 interface. The SMF 183a, 183b may select and control the UPF 184a, 184b and configure the routing of traffic through the UPF 184a, 184b. The SMF 183a, 183b may perform other functions, such as managing and allocating WTRU IP addresses, managing PDU sessions, controlling policy enforcement and QoS, providing downlink data notifications, and the like. A PDU session type may be IP-based, non-IP based, Ethernet-based, and the like.

[0072] The UPF 184a, 184b may be connected to one or more of the gNBs 180a, 180b, 180c in the RAN 113 via an N3 interface, which may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices. The UPF 184, 184b may perform other functions, such as routing and forwarding packets,enforcing user plane policies, supporting multi-homed PDU sessions, handling user plane QoS, buffering downlink packets, providing mobility anchoring, and the like.

[0073] The CN 115 may facilitate communications with other networks. For example, the CN 115 may include or may communicate with an IP gateway (e.g., an IP multimedia subsystem (IMS) server) that serves as an interface between the CN 115 and the PSTN 108. In addition, the CN 115 may provide the WTRUs 102a, 102b, 102c with access to the other networks 112, which may include other wired and / or wireless networks that are owned and / or operated by other service providers. In one embodiment, the WTRUs 102a, 102b, 102c may be connected to a local Data Network (DN) 185a, 185b through the UPF 184a, 184b via the N3 interface to the UPF 184a, 184b and an N6 interface between the UPF 184a, 184b and the DN 185a, 185b.

[0074] In view of Figures 1 A-1 D, and the corresponding description of Figures 1 A-1 D, one or more, or all, of the functions described herein with regard to one or more of: WTRU 102a-d, Base Station 114a-b, eNode-B 160a-c, MME 162, SGW 164, PGW 166, gNB 180a-c, AMF 182a-ab, UPF 184a-b, SMF 183a-b, DN 185a-b, and / or any other device(s) described herein, may be performed by one or more emulation devices (not shown). The emulation devices may be one or more devices configured to emulate one or more, or all, of the functions described herein. For example, the emulation devices may be used to test other devices and / or to simulate network and / or WTRU functions.

[0075] The emulation devices may be designed to implement one or more tests of other devices in a lab environment and / or in an operator network environment. For example, the one or more emulation devices may perform the one or more, or all, functions while being fully or partially implemented and / or deployed as part of a wired and / or wireless communication network in order to test other devices within the communication network. The one or more emulation devices may perform the one or more, or all, functions while being temporarily implemented / deployed as part of a wired and / or wireless communication network. The emulation device may be directly coupled to another device for purposes of testing and / or may perform testing using over-the-air wireless communications.

[0076] The one or more emulation devices may perform the one or more, including all, functions while not being implemented / deployed as part of a wired and / or wirelesscommunication network. For example, the emulation devices may be utilized in a testing scenario in a testing laboratory and / or a non-deployed (e.g., testing) wired and / or wireless communication network in order to implement testing of one or more components. The one or more emulation devices may be testing equipment. Direct RF coupling and / or wireless communications via RF circuitry (e.g., which may include one or more antennas) may be used by the emulation devices to transmit and / or receive data.

[0077] For a Remote WTRLI to discover a U2N (e.g., WTRU to network) relay via a U2U (e.g., WTRU to WTRU) Relay in proximity, the discovery messages transmitted via a U2U Relay (also known as "intermediate Relay") need to be securely protected. Failure to protect the security of these discovery messages may lead to various attacks by unauthorized Relays / WTRUs (e.g., discovery message tampering or potential leakage of privacy sensitive information). The 5GS needs to provide mechanisms to protect (for confidentiality, integrity, and against replay) the discovery messages for the Remote WTRU to discover the U2N Relay via the U2U Relay.

[0078] The 3GPP system must protect the security (e.g., integrity and confidentiality) of information between the Remote WTRU and the U2N Relay via the U2U Relay. Failure to protect the integrity and confidentiality of information exchanged between the Remote WTRU and the network over the U2N Relay via a U2U Relay may lead to various attacks by unauthorized WTRU / Relays, such as unauthorized disclosure and modification of information. In current U2N security procedures, the Remote WTRU is provisioned with or generates (respectively in the UP and CP case) an individual ProSe Remote User Key (PRUK) key specific to that Remote WTRU and Relay Service Code (RSC) to be able to connect with a U2N Relay for a particular RSC. A valid PRUK Key is required to allow the connection to a U2N Relay. How an L3 U2U Relay can provide connectivity service for a Remote WTRU using a U2N Relay without a valid PRUK key is currently not defined.

[0079] Furthermore, the PRUK ID of the Remote WTRU is also passed on by the U2N Relay to the SMF for Remote WTRU identification purposes. How to enable the identification of a Remote WTRU in the 5GCN connected via an L3 U2U Relay is alsocurrently not defined. The 5GS needs to provide mechanisms to establish a secure communication link between the Remote UE and the U2N Relay via a U2U Relay.

[0080] FIG. 2 is a block diagram 200 illustrating a PC5 key hierarchy for 5G ProSe U2N Relay security over the UP. FIG. 2 illustrates the key hierarchy defined for the UP based approach. The PKMF 202 and Remote WTRU 204 derive from UP-PRUK 206 a KNRP 208 used as the root key for the PC5 link between the Remote WTRU 204 and the U2N Relay 206. The PKMF 202 may provide the KNRP 208 to the U2N Relay 210 via UP during a key request procedure, while the Remote WTRU 204 derives KNRP 208 during the direct security establishment procedure (DSMC) over the PC5 link with the U2N Relay 210. The Remote WTRU 204 and U2N Relay 210 further derive the session key and / or security keys from KNRP 208 during a DSMC procedure.

[0081] A similar key hierarchy may be defined for the CP approach. The main difference is that the AUSF and the Remote WTRU derive the rook credential (CP-PRUK) during a ProSe authentication procedure via the U2N Relay and / or non-access stratum (NAS) messaging.

[0082] A U2U Relay discovery and / or communication security may be implemented. For example, 3GPP has defined U2U procedures for discovery and / or communication, including security and / or privacy. Similar to U2N Relay, the U2U relay supports Model A and / or B of discovery. In Model A, the U2U Relay may send U2U Relay announcement messages that include information about End WTRUs. This information about End WTRUs may also be known as direct discovery set. This information may include user info and / or a ProSe service code. This information may have been previously received via a prior discovery procedure and / or through a connection to the U2U Relay. In Model B, the U2U Relay may re-transmit a direct discovery set included in U2U Relay discovery solicitation and / or response messages.

[0083] Discovery messages may be protected using two separate key sets. A first key set may be associated with the RSC offered by the U2U Relay and / or used to protect the U2U Relay discovery message (e.g., announcement and / or solicitation). A second key set may be associated with the ProSe service used by the End WTRUs communicating via the U2U Relay and / or used to protect the direct discovery set within a U2U Relay discovery message. Both discovery messages and / or direct discovery setinside the message may be protected for confidentiality, integrity, and / or against replay. Replay protection is based on a UTC time based counter.

[0084] Multi-hop for U2N and / or U2U Relay may be implemented as described herein. For example, multi-hop for U2N Relay may enable a Remote WTRU to discover and / or communicate with a U2N Relay via one or more U2U relays. Multi-hop U2U Relay may enable End WTRUs to discover and / or communicate with each other via more than one U2U Relay.

[0085] The multi-hop capability may be deemed crucial for mission critical communications (e.g., first responders). The multi-hop capability is generally needed to enhance coverage (e.g., indoor).

[0086] Issues in multi-hop U2N Relay discovery security may need to be addressed.For example, such issues may include how the Remote WTRU / U2U Relay is authorized for relayed U2N Relay discovery; what security keys the remote WTRU, U2U relay, and / or U2N relay may use in relayed U2N Relay discovery procedures ; and / or support for relayed U2N discovery via one or more U2U Relays.

[0087] Issues in multi-hop U2N Relay communication security may need to be addressed. For example, such issues may include how the Remote WTRU is authorized for relayed U2N Relay communications; how the relayed U2N communication security is established between the Remote WTRU, U2U Relay and / or U2N Relay; how to consider L3 and / or L2 Relays; and / or support for relayed communication via one or more U2U Relays.

[0088] A U2U Relay may use the hop count (HC) parameter associated with a U2N Relay discovery set to determine the handling of the U2N Relay discovery set in discovery messages (e.g., forward, ignore, and / or announce). The Remote WTRU may use the HC associated with a particular U2N Relay service to select and / or prioritize a multi-hop path toward a U2N Relay providing that service.

[0089] The proposed HC based mechanism enables multiple U2U Relays involved in the discovery to coordinate, for example, which U2U Relay may initiate announcements of U2N Relay discovery sets or simply re-transmit these sets. This mechanism may prevent excess discovery messaging by ensuring only U2U Relays in direct proximity (e.g., with HC=1 from U2N Relay) to the U2N Relay can initiate U2U Relayannouncement messages. The intermediate U2U Relays also may ensure the preservation of the freshness (based on UTC time based counter) of the U2N Relay discovery set. The intermediate U2U Relays may forward the U2N relay discovery set close to real time in a discovery message when not in direct proximity with the U2N Relay (e.g., HC>1 in the received discovery message). The HC based mechanism also may enable the U2U Relay to filter broadcast discovery messages to avoid discovery message broadcast “loops” and / or “storms” (e.g., if stored HC < received HC).

[0090] A Remote WTRU may connect to the U2N Relay via one or more U2U Relays. The Remote WTRU may use a single hop credential (e.g., UP-PRUK) to generate a fresh intermediate key (e.g., PRK) passed securely to the U2U Relay. The U2U relay may then connect with the U2N Relay on behalf of Remote WTRU using the intermediate key. Reuse of the single hop credential may preserve the existing single key provisioning mechanism (e.g., with PKMF). The Remote WTRU may use a multihop specific credential (e.g., MUP-PRUK) to generate a fresh intermediate key (e.g., PRK) passed securely to the U2U Relay. The U2U Relay may then connect with the U2N Relay on behalf of the Remote WTRU using the intermediate key. Using a multihop specific root credential decoupled from the single-hop root credential may allow the PKMF to manage (e.g., revoke) authorization for multi-hop independently from singlehop. For example, MUP-PRUK may be provisioned with a different validity scope (e.g., VPLMN, time, and / or area) than UP-PRUK. The PKMF may determine that the connection is multi-hop based on the MUP-PRUK ID alone. This determination may be leveraged to preserve the existing protocol messages between the U2N Relay and PKMF and / or keep the multi-hop connectivity transparent to the U2N Relay.

[0091] The Remote WTRU using an intermediate key with the U2U Relay may ensure the forward secrecy for Remote WTRU communications (as opposed to if the U2U Relay was provided with the PRUK key directly). For example, should a PRK (PRK#1 ) given to a particular U2U Relay be compromised and / or leaked, an attacker may not obtain from that PRK#1 the UP-PRUK and / or a different PRK (PRK#2) used to connect via another U2U Relay (e.g., to replay and / or decrypt recorded conversations using PRK#2).

[0092] Multi-hop U2N Relay discovery security may also be implemented. The discovery security may provide a multi-Hop for U2N Relay discovery using a U2N Relay discovery set with HC. This implementation may comprise U2U Relays using a HC associated with a U2N Relay discovery set to determine how to handle (e.g., forward or discard and / or announce) U2N Relay discovery sets during U2U Relay discovery procedures. The U2N Relay discovery set may include user info of the Remote UE or U2N Relay and / or U2N_RSC.

[0093] If the U2U Relay is in direct proximity to a U2N Relay, the implemented steps may include the U2U Relay being provisioned with a U2U Relay service code (U2U_RSC) with an associated indication for multi-hop support. The U2U Relay may receive a first U2U Relay discovery message from a U2N Relay. The discovery message may include the U2U_RSC and / or a U2N Relay discovery set. The U2U Relay may store an initial HC (e.g., direct, single-hop, and / or HC=1 ) along the U2N Relay discovery set and / or source L2 ID of the U2N Relay if the relay indication is set in received discovery message. The U2U Relay may send a second U2U Relay discovery message including an updated HC (e.g., indirect, multi-hop, incremented from first HC) associated with the U2N Relay discovery set. The U2U Relay may protect the HC as part of the discovery message protection. The U2U Relay may initiate announcements of U2N Relay discovery set if the stored HC associated with the U2N Relay discovery set indicates direct proximity (e.g., HC=1 ) and / or refrains if HC indicates indirect proximity (e.g., HC>1 ), for example, in Model A.

[0094] If an intermediate U2U Relay is needed, the implemented steps may include the U2U Relay being provisioned with a U2U_RSC with an associated indication for multihop support. The intermediate U2U Relay may receive a first U2U Relay discovery message from a U2U Relay. The discovery message may include U2U_RSC and / or one or more U2N Relay discovery sets, each with an associated HC. For each U2N Relay discovery set received, the intermediate U2U Relay may determine whether to forward the discovery set based on a comparison performed between the HC in the message and / or any HC already stored with the U2N Relay discovery set. Based on the forwarding determination, the intermediate U2U Relay may send a second U2U Relay discovery message including one or more updated HC (e.g., incremented from receivedHC) associated with the corresponding one or more U2N Relay discovery sets. The U2U intermediate Relay may protect the HC as part of the discovery message protection.

[0095] For the security of U2U Relay discovery messages used for U2N Relay discovery, the principle of two separate discovery security key sets (or key material) may be used. A first key set may be associated with U2U_RSC and / or used to protect U2U Relay discovery messages. A second key set may be associated with U2N_RSC and / or used to protect U2N Relay discovery set transported in the U2U Relay discovery messages. The U2N Relay discovery set may include U2N_RSC and / or user info of Remote WTRU / U2N Relay. The key material may consist of one or more keys (e.g., confidentiality, integrity keys, and / or timing parameters for replay protection). In addition to the security key material associated with U2N_RSC, the network (e.g., PKMF and / or DDMF) may provision the U2N Relay with the security key material associated with U2U_RSC. This material may be used during U2U Relay discovery. The Remote WTRU may also be provisioned with both key sets (U2N_RSC and U2U_RSC).

[0096] The Remote WTRU and / or the U2N Relay may use the U2N_RSC security key material for the protection of U2N discovery set inside a U2U relay discovery message protected using U2U_RSC key material. The U2U Relay may use the U2U_RSC key material for the processing of security of the received U2U relay discovery messages and / or the protection of the transmitted U2U relay discovery messages. In such cases, the U2U Relay may include the protected U2N discovery set as received from Remote WTRU / U2N Relay.

[0097] The U2U_RSC may be used for both ProSe service and U2N Relay service connectivity. Accordingly, the U2U Relay may mix U2N Relay and direct discovery sets inside U2U Relay announcement messages.

[0098] FIG. 3 is a block diagram 300 illustrating an example Model A based U2U Relay discovery for U2N Relay using hope count based selection / fi Itering. As shown, the U2N Relay may decide to announce the U2N_RSC that it offers. The U2U Relays may use a HC associated with a U2N Relay discovery set to determine how to handle U2N Relay discovery sets (e.g., forward or discard, announce).

[0099] At 302, the U2N Relay 304 may send a U2U Relay announcement message which includes a relay indication to indicate that the announcement message may be relayed via U2U Relay(s). The announcement (e.g., discovery) message may include an initial HC (e.g., HC=1 ) associated with a U2N Relay discovery set also included in the U2U Relay discovery message. The U2N Relay 304 may protect the U2N Relay 304 discovery set using the key material associated with the U2N_RSC. The U2N Relay 304 may protect the U2U Relay discovery message using the key material associated with the U2U_RSC.

[0100] In FIG. 3, a first U2U Relay, referred to as U2U Relay #1 306 in FIG. 3, may process the security of the received discovery message from the U2N Relay 304 using the key material associated with the U2U_RSC. During this processing, the U2U Relay #1 306 may check integrity and / or freshness of the discovery message. The U2LI Relay #1 306 may decrypt the discovery message. The U2U Relay may store an initial HC associated with the U2N Relay discovery set and / or a source L2 ID of the U2N Relay if the relay indication is set in the received discovery message. The first relay may be different than subsequent relays as the first relay may allocate an initial HC. Subsequent relays may increment HC. Subsequent relays may select the path to a U2N Relay based on the received HC value. The U2U Relay may set the initial HC value. The U2N Relay may set the initial HC value in the U2U discovery message. The U2U Relays may store the U2N Relay discovery set along with HC. The U2U Relays may consider this information as expired past a certain time (e.g., based on a timer and / or UTC time based counter associated with the U2N Relay discovery set in the discovery message).

[0101] In FIG. 3, the U2U Relay #1 306 may re-transmit the U2N Relay 304 discovery set in a new U2U Relay discovery message. The U2U Relay #1 306 may include an updated HC (e.g., indirect, multi-hop, and / or incremented from the first HC) associated with the U2N Relay discovery set in the message. The U2U Relays may protect the updated HC as part of the U2U Relay discovery message protection (e.g., using the key material associated with the U2U_RSC).

[0102] At 308, a U2U Relay #2 310 may receive a discovery message from the U2N Relay 304 and / or process the message the same way as the U2U Relay #1 306.Specifically, U2U Relay #2 310 may process the security and / or stores the U2N Relay 304 discovery set, the associated initial HC, and / or source L2 ID of the U2N Relay 304.

[0103] At 312, the U2U Relay #2 310 may receive a discovery message from the U2U Relay #1 306 carrying the U2N Relay 304 discovery set with an associated HC. The U2U Relay #2 310 may process the security and / or store the U2N Relay 304 discovery set, associated HC, and / or source L2 ID of the U2U Relay. The U2U Relay #2 310 may determine whether to re-transmit the U2N Relay discovery set based on a comparison of U2N Relay discovery set HCs performed between the HC in the message and the associated stored HC.

[0104] The U2U Relay #2 310 may detect that it already has a direct proximity to the U2N Relay based on the stored HC compared to the received HC from the U2U Relay #1 306. The LI2U Relay #2 310 may then determine to ignore the U2N Relay 304 discovery set in the discovery message from the U2U Relay #1 306.

[0105] At 314 and 316, the U2U Relay #2 310 may send U2U Relay 310 announcement messages, including the U2N Relay 304 discovery set from U2N Relay 304 with associated HC.

[0106] At318, a U2U Relay #3 320 may receive a discovery message from the U2U Relay #1 306. At step 314, the U2U Relay #3 320 may receive a discovery message from the U2U Relay #2 310. After receiving the discovery messages, the U2U Relay #3 320 may process the discovery messages as described above. Specifically, U2U Relay #3 320 may process the security and / or storing the U2N Relay 304 discovery set, associated received HC, and / or source L2 ID.

[0107] The U2U Relay #3 320 then may determine that the U2U Relay #1 306 and the U2U Relay #2 310 may be at the same number of hops distance from the U2N Relay 304 based on received HC. Based on this determination, the U2U Relay #3 320 may decide to select and store one of the U2U Relays L2 ID information along with the U2N Relay 304 discovery set (e.g., based on discovery message signal strength) or both U2U Relay L2 ID information, which the U2U Relay may use provide redundant communication path towards the U2 Relay 304.

[0108] At 322, the U2U Relay #3 320 may send a U2U Relay announcement message. The U2U Relay announcement message may include the selected U2N Relay discovery set with associated HC.

[0109] A Remote WTRLI 324 may receive a discovery message from both the U2U Relay #2 310 (at 316) and / or the U2U Relay #3 320 (at 322). The Remote WTRU 324 may process the discovery messages as described above for U2U Relays (e.g., processing the security and / or storing U2N Relay discovery set and / or associated received HC).

[0110] The Remote WTRU may determine that the U2U Relay #2 310 and the U2U Relay #3 320 may be at a different number of hops distance from the U2N Relay 304. Based on the HC, the Remote WTRU 324 may decide to select and / or store one of the U2U Relays L2 ID information along the U2N Relay 304 discovery set based on lower HC value or both U2U Relay L2 ID information. The Remote WTRU 324 may use this information as a means to enable redundant communication path towards the U2N Relay 304. In that case, the Remote WTRU 324 may decide to connect to the U2N Relay 304 in priority via the U2U Relay with a lower associated HC value (e.g., U2U Relay #2 310 in this case).

[0111] In FIG. 3, the discovery messages may include a single U2N Relay 304 discovery set. However, in the presence of multiple U2N Relays, the discovery messages may include as many corresponding U2N Relay discovery sets.

[0112] The solution above may be applied to Model B (e.g., solicitation from Remote WTRU and / or response from U2N Relay). A Remote WTRU may decide to discover the U2N offering U2N_RSC via solicitation message. The U2U Relays may use a HC associated with a U2N Relay discovery set to determine how to handle U2N Relay discovery sets (e.g., forward or discard, announce) in the solicitation message.

[0113] For Model A, at any point in time after discovering the U2N Relay, the U2U Relay may decide to initiate announcements of a U2N Relay discovery set if the stored HC associated with the U2N Relay discovery set indicates a direct single-hop proximity (e.g., HC=1 ) and / or refrains if HC indicates a multi-hop proximity (e.g., HC>1). This mechanism may prevent excess discovery messaging by ensuring only U2U Relays in direct proximity to the U2N Relay can initiate U2U Relay announcement messages forthe U2N Relay. At the same time, intermediate U2U Relays not in direct proximity, based on associated HC (received / stored), may determine to re-transmit the U2N Relay discovery set in the received announcement message in real-time. This re-transmission is required to preserve the freshness (based on UTC time based counter) of the U2N Relay discovery set while the intermediate U2N Relay announces the re-transmission. The latter needs to rely on the U2U Relay in direct proximity to obtain a fresh U2N Relay discovery set (e.g., requested from a connected U2N Relay).

[0114] In examples, the discovery messages sent and / or received by the U2N Relay may remain similar whether single-hop or multi-hop discovery of the U2N Relay is performed, with the following differences described herein. The U2U Relay may be provisioned with both discovery key sets, respectively, for U2U_RSC and U2N_RSC. The U2N Relay may be provisioned with the discovery key set for U2N_RSC as per existing procedures.

[0115] For Model A, the U2N Relay announcement message may include U2N_RSC. The U2N Relay may be protected using the associated key set. The U2N Relay may include a relay indication to indicate that multi-hop discovery is allowed (e.g., one or more U2U Relay may be involved in the discovery procedure).

[0116] For Model A, if the U2U Relay receives an announcement message from the U2N Relay, the U2U Relay may process its security (e.g., decrypts, checks integrity and / or freshness) using the key set associated with U2N_RSC. If the message includes a relay indication, the U2U Relay may protect the received U2N Relay discovery set using the key set associated with U2N_RSC Moreover, the U2U Relay may include the key set associated with U2N_RSC along with its associated HC in a LI2U Relay announcement message. The U2U Relay may protect the transmitted announcement message using the key set associated with U2U_RSC.

[0117] For Model A, if the U2U Relay receives an announcement message from another U2U Relay, the U2U Relay may process its security using the key set associated with U2U_RSC. The U2U Relay may choose to process the security of the U2N Relay discovery set within the message for delayed re-transmission (e.g., for grouping with other discovery sets in a single announcement message) and / or re-transmit in real timeas described above (e.g., for end-to-end security processing performed at the Remote WTRU only).

[0118] For Model B, the U2U Relay in direct proximity to the U2N Relay may receive a U2U Relay discovery solicitation message from a U2U Relay and / or Remote WTRLI, including a protected U2N Relay discovery set. The U2U Relay may process the message security (e.g., decrypts, checks integrity and / or freshness) using the key set associated with U2U_RSC. The U2U Relay may process the security of the included U2N Relay discovery set using the key set associated with U2N_RSC. The U2U Relay may send the received U2N Relay discovery set in a U2N Relay discovery solicitation message protected using the key set associated with U2N_RSC.

[0119] For Model B, the U2U Relay in direct proximity to the U2N Relay may receive a U2N Relay discovery solicitation response message from a U2N Relay, including a U2N Relay discovery set. The U2U Relay may process the message security (e.g., decrypts, checks integrity and / or, freshness) using the key set associated with U2N_RSC. The U2U Relay may protect the received U2N Relay discovery set using the key set associated with U2N_RSC. Moreover, the U2U Relay may include the key set associated with U2N_RSC along with its associated HC in a U2U Relay discovery solicitation response message. The U2U Relay may protect the transmitted discovery message using the key set associated with U2U_RSC.

[0120] Multi-hop U2N Relay communication security using a single-hop credential UP- PRLIK may be implemented as described herein. This implementation may include the Remote WTRU deciding to connect to U2N Relay via a U2U Relay and / or sending a PRLIK ID and / or a new intermediate key (e.g., PRK) to the LI2U Relay after the PC5 link security is established with the U2U Relay. The new intermediate key (e.g., PRK) may be derived from a single-hop root credential PRUK. The U2U Relay may connect with U2N Relay on behalf of the Remote WTRU using the intermediate key and / or PRUK ID received from the Remote WTRU and / or an intermediate U2U Relay.

[0121] The PCF may provision the Remote WTRU with U2N_RSC with multi-hop support indicator. The PKMF may provision the Remote WTRU with UP-PRUK ID and / or UP-PRUK associated with U2N_RSC. The Remote WTRU may discover U2N Relay via the U2U Relay (for use in Model A or B). The Remote WTRU may send aDCR message to the U2U Relay including U2U_RSC, U2N_RSC, and / or user info (Remote WTRU, U2N Relay, U2U Relay). The Remote WTRLI may perform mutual authentication with U2U Relay (e.g., using Long Term Credential). The Remote WTRU may receive a direct security mode (DSM) command message from the U2U Relay. The Remote WTRU may derive a new PRK using UP-PRUK and / or noncel . The Remote WTRU may send to the U2U Relay a DSM complete message with confidentiality and / or integrity protected, including UP-PRUK ID / PRK and / or noncel . The Remote WTRU may receive a DCA message from U2U Relay confirming a successful connection with the U2N Relay.

[0122] A PCF may provision a U2U Relay in direct proximity to a U2N Relay by PCF with U2N_RSC with multi-hop support indicator (e.g., Relay is authorized to provide connectivity to U2N Relay for that U2N_RSC). The U2U Relay may receive a DCR message from a Remote WTRU including U2U_RSC, U2N_RSC, user info of Remote WTRU, U2N Relay, and / or U2U Relay. The U2U Relay may perform mutual authentication with Remote WTRU (e.g., using a LTC). The U2U Relay may send a DSM command message to the Remote WTRU. The U2U Relay may receive a DSM complete message from the Remote WTRU including UP-PRUK ID / PRK and / or noncel . The U2U Relay may send a DCR message including UP-PRUK ID, noncel , and / or a U2U relay indication to the U2N Relay. The U2U Relay may receive a DSM Command message from the U2N Relay including nonce2. The U2U Relay may derive a fresh KNRP using PRK and / or nonce2. The U2U Relay may derive the session and / or security keys using KNRP. The U2U Relay may send a DSM Complete message to the U2N Relay. The U2U Relay may receive a DCA message from U2N Relay. The U2U Relay may send a DCA message to the Remote WTRU confirming successful connection with the U2N Relay.

[0123] The PKMF of the Remote WTRU may send a UP-PRUK and / or UP-PRUK ID in a key response message to a Remote WTRU upon receiving a key request message from the Remote WTRU. The PKMF of the Remote WTRU may receive a key request message from a U2N Relay via Relay’s PKMF, including UP-PRUK ID, U2N_RSC, noncel , and / or a U2U Relay indication. The PKMF of the Remote WTRU may determine that the Remote WTRU is requesting to connect to the U2N Relay via one ormore U2U Relay, based on the U2U Relay indication. Based on the determination, the PKMF of the Remote WTRU may derive a fresh PRK from UP-PRUK using noncel and / or a fresh KNRP from PRK using a nonce2. The PKMF of the Remote WTRU may send the KNRP and / or nonce2 to the U2N Relay via Relay’s PKMF.

[0124] The U2N security procedure and / or related key hierarchy to enable multi-hop for U2N Relay may be enhanced. The PKMF of the Remote WTRU and / or U2U Relay are enhanced respectively to derive an intermediate fresh key (PRK) from UP-PRUK and / or use PRK for PC5 link security establishment with the U2N Relay. An intermediate key may prevent the propagation of the root credential UP-PRUK to a potentially high number of U2U when the Remote WTRU needs to send its UP-PRUK to the U2U Relay for multi-hop U2N Relay connectivity. In that case, the UP-PRUK may be exposed to a risk of leakage should any of the U2U Relays be compromised.

[0125] FIG. 4 is a block diagram 400 illustrating an example PC5 key hierarchy for 5G ProSe U2N Relay security over the UP enhancements for multi-hop support. At 402, the Remote WTRU 404 may derive PRK 406 from UP-PRUK 408 when establishing the security for the PC5 link with the U2U Relay 410 and passes PRK 406 securely to the U2U Relay 410.

[0126] At 402, the PKMF 412 of the Remote WTRU 404 may derive PRK 406 from UP- PRUK 408 when requested by the U2N Relay 414 (e.g., using a key request message) with an indication that Remote WTRU 404 is connecting via a U2U Relay 410. At 416, the PKMF 412 of the Remote WTRU 404 may further derive KNRP 418 from PRK 406 and / or pass KNRP 418 to the U2N Relay 414.

[0127] At 416, the U2U Relay 410 may use PRK 406 to generate a KNRP 418 during the PC5 link security establishment procedure with the U2N Relay 414.

[0128] For end-to-end security between the Remote WTRU 404 and the U2N Relay 414 or the network (e.g., N3IWF), application layer security mechanisms (e.g., using IPsec / IKEv2) may be used.

[0129] FIGs. 5A-5B are flow diagrams 500 that illustrate an example PC5 security establishment procedure for 5G ProSe WTRU -to- Network (U2N) relay communication over the UP with enhancements for multi-hop. The procedure is illustrated with a single U2U Relay, but support for multiple U2U Relays may be possible with this solution.

[0130] As shown in FIG. 5A at 504a-c, the Remote WTRU, U2U Relay, and U2N Relay, respectively, are each provisioned with U2U / U2N Relay discovery and / or communication parameters by PCF, DDNMF, and / or PKMF. The Remote WTRU authorized for multi-hop discovery and / or communication may be provisioned with U2U Relay and / or U2N Relay discovery and / or communication parameters. The Remote WTRU and / or U2N Relay may be provisioned with U2U_RSC and / or U2N_RSC. Each RSC may be associated with a multi-hop support indicator. The U2U Relay may be provisioned with U2U_RSC associated with a multi-hop support indicator.

[0131] At 508a, the Remote WTRU may send a ProSe remote user key request to its PKMF. The Remote WTRU may send the request with an indication that the Remote WTRU wants to communicate with a U2N Relay via U2U Relay. At 508b, the PKMF of the Remote WTRU may verify that the Remote WTRU is authorized for U2N Relay services, including via multi-hop. At 508c, if the Remote WTRU is authorized, the PKMF of the Remote WTRU may send a response including UP-PRUK and / or UP- PRUK ID to the Remote WTRU.

[0132] At 512, the Remote WTRU may discovers the U2N Relay via the U2U Relay discovery messages. At 516, the Remote WTRU may send a DCR message to the U2U Relay. The DCR message may include the U2U_RSC, U2N_RSC, user info of U2N Relay, and / or UP-PRUK ID.

[0133] At 520, the Remote WTRU and U2U Relay may perform mutual authentication using a LTC. Additionally or alternatively, the Remote WTRU and / or U2U Relay may connect with network assistance (with U2U Relay in coverage) and / or skip mutual authentication. In that case, the Remote WTRU may pass an additional UP-PRUK ID associated with the U2U_RSC connectivity in the DCR message sent to the U2U Relay.

[0134] At 524a, the Remote WTRU may receive a DSM command message from the U2U Relay that may include conventional security parameters (e.g., security policy, freshness parameters, etc.) to initiate the PC5 link security establishment.

[0135] At 524b, based on the Remote WTRU connecting to the U2N Relay via a U2U Relay, The Remote WTRU may derive a PRK from UP-PRUK. The Remote WTRU may use as an input to the derivation function a noncel . The Remote WTRU may use U2U_RSC in the derivation as well to bind the PRK to a particular U2U Relay service.

[0136] At 524c, the Remote WTRU may send a DSM complete message to the U2U Relay, including PRK and / or noncel . The message may be fully protected (e.g., encrypted, integrity, replay) to avoid any potential exposure of PRK to an eavesdropper.

[0137] If more than one LI2U Relay is involved, the intermediate U2U Relay may act as the Remote WTRU toward the next U2U Relay (except for the PRK derivation). The intermediate U2U Relay may forward the PRK to the next U2U Relay in the chain.

[0138] FIG. 5B is a continuation flow diagram 500 initially depicted in FIG. 5A. As shown in FIG. 5B at 528, the U2U Relay may send a DCR message to the U2N Relay. The DCR message may include UP-PRUK ID, U2N_RSC, U2N user info, noncel , and / or a U2U Relay indication to indicate the connection request is from a Remote WTRU via U2U Relay.

[0139] At 532a, the U2N Relay may send a key request to the Remote WTRU PKMF via U2N Relay PKMF. The request includes UP-PRUK ID, U2N_RSC, noncel , and the U2U Relay indication. The Remote WTRU PKMF may be located for routing information in the UP-PRUK ID.

[0140] At 532b, if U2U_RSC is used for PRK derivation as described at 524a-c, the U2U_RSC may be passed to the Remote WTRU PKMF via the U2N Relay and its PKMF. The PKMF may also use the U2U_RSC as an input parameter to the derivation of PRK.

[0141] At 532c, based on the presence of the U2U Relay indication, the Remote WTRU PKMF may derive a PRK from UP-PRUK using noncel . The Remote WTRU PKMF may also derive a KNRP from PRK using a nonce2.

[0142] The PKMF may also use the presence of U2U Relay indication to not attempt the generation of a new UP-PRUK using the generic bootstrapping architecture (GBA) PUSH mechanism. The PKMF may determine this knowing that the connecting U2U Relay cannot perform such a procedure which may require the Remote WTRU main network access credential (in the universal integrated circuit card (UICC)). In case of the need to generate a new UP-PRUK, the PKMF may decide to reject the key request with an error code. The error code may indicate that a fresh UP-PRUK is required for multihop connectivity. The Remote WTRU may use such an error code to request a freshUP-PRUK from its PKMF while in coverage and / or connect via a U2N Relay directly to generate a new one using GBA PUSH.

[0143] At 532d-e, the Remote WTRU PKMF may send the KNRP and / or the nonce2 to the U2N Relay via U2N Relay PKMF.

[0144] At 536a, the U2N Relay may send an integrity protected DSM Command message to the U2U Relay, including nonce2. At 536b, the U2U Relay may derive KNRP from PRK using nonce2. The U2U Relay may derive a session key and / or security keys. The U2U Relay may verify the security of the DSM command with the generated security keys. The U2U Relay may determine that both the Remote WTRU and / or U2N Relay are authorized for multi-hop U2N Relay connectivity if the verification is successful. At 536c, the U2U Relay may send a protected (e.g., for confidentiality and / or integrity) DSM complete message to the U2N Relay. At 536d, the U2N Relay may verify the security of the DSM command with the generated security keys. The U2N Relay may determine that both the Remote WTRU and / or the U2U Relay are authorized for multi-hop U2N Relay connectivity if the verification is successful.

[0145] At 540a, the U2N Relay may send a DCA message to the U2U Relay confirming a successful relayed connection. At 540b, the U2N Relay may proceed with the following steps to complete the procedure (e.g., IP address allocation). The U2N Relay may provide 5GC with UP-PRUK ID during a Remote WTRU Report procedure to identify the Remote WTRU using the multi-hop U2N Relay connectivity service. At 540c, the U2U Relay may send a DCA message to the Remote WTRU confirming a successful multi-hop relayed connection.

[0146] As shown in FIGs. 5A-5B, the key hierarchy and / or procedures are illustrated using the UP approach and UP-PRUK. The solution may be applied equally using the CP approach with the following differences described herein. Instead of UP-PRUK and / or UP-PRUK ID, the Remote WTRU may uses a CP-PRUK and / or CP-PRUK ID that it possesses (from a previous connection with the U2N Relay). On the network side, AUSF may derive PRK from CP-PRUK instead of PKMF.

[0147] Multi-hop U2N Relay communication security using a multi-hop credential MUP- PRUK may be implemented. The implemented steps may include the Remote WTRU deciding to connect to U2N Relay via a U2U Relay and / or sending to the U2U Relay aPRUK ID and a new intermediate key (PRK) derived from a multi-hop root credential (MUP-PRUK). The MUP-PRUK may be used for U2N Relay connectivity via U2U Relay after PC5 link security is established with U2U Relay. The U2U Relay may connect with U2N Relay on behalf of Remote WTRLI using the intermediate key and / or MUP-PRUK ID received from Remote WTRU and / or an intermediate U2U Relay.

[0148] In this implementation, the PCF may provision the Remote TRU with U2N_RSC with a multi-hop support indicator. The Remote WTRU may send a key request to its PKMF with an indication for multi-hop U2U connectivity. The Remote WTRU may receive from its PKMF an UP-PRUK / UP-PRUK ID (e.g., for conventional direct U2N Relay connectivity) and / or an MUP-PRUK ID / MUP-PRUK to be used for multi-hop U2N Relay connectivity. The Remote WTRU may discover U2N Relay via the U2U Relay (e.g., Model A or B). The Remote WTRU may send a DCR message to the U2U Relay including U2U_RSC, U2N_RSC, user info (e.g., Remote WTRU, U2N Relay, U2U Relay). The Remote WTRU may perform mutual authentication with U2U Relay (e.g., using Long Term Credential). The Remote WTRU may receive a DSM Command message from the U2U Relay. The Remote WTRU may derive a new ProSe Relay Key (PRK) using MUP-PRUK and / or noncel . The Remote WTRU may send to the U2U Relay a DSM complete message that confidentiality and / or integrity are protected, including MUP-PRUK ID / PRK, noncel . The Remote WTRU may receive a DCA message from U2U Relay confirming a successful connection with the U2N Relay.

[0149] A PCF may provision a U2U Relay in direct proximity to a U2N Relay with U2N_RSC and / or with multi-hop support indicator (e.g., the Relay is authorized to provide connectivity to U2N Relay for that U2N_RSC). The U2U Relay may receive a DCR message from a Remote WTRU including U2U_RSC, U2N_RSC, user info of Remote WTRU, U2N Relay, and / or U2U Relay. The U2U Relay may perform mutual authentication with Remote WTRU (e.g., using a LTC). The U2U Relay may send a DSM command message to the Remote WTRU. The U2U Relay may receive a DSM Complete message from Remote WTRU including MUP-PRUK ID / PRK, noncel . The U2U Relay may send a DCR including MUP-PRUK ID, noncel to the U2N Relay and / or complete PC5 link security establishment as per existing procedure. The U2U Relaymay receive a DCA message from U2N Relay. The U2U Relay may send a DCA message to Remote WTRU confirming a successful connection with the U2N Relay.

[0150] The PKMF of the Remote WTRU may send a multi-hop specific credential MUP- PRUK / MUP-PRUK ID (e.g., along UP-PRUK / UP-PRUK ID) in a key response message to a Remote WTRU upon receiving a key request message from the Remote WTRU including a multi-hop indication. The PKMF of the Remote WTRU may receive a key request message from a U2N Relay via Relay’s PKMF, including MUP-PRUK ID, U2N_RSC, and / or noncel . The PKMF of the Remote WTRU may determine that the Remote WTRU is requesting to connect to the U2N Relay via one or more U2U Relays, for example. The request to connect may be based on the MUP-PRUK ID being associated with a multi-hop specific credential. Based on the determination, the PKMF of the Remote WTRU may derive a PRK from MUP-PRUK using noncel . The PKMF of the Remote WTRU may derive a KNRP from PRK using a nonce2. The PKMF of the Remote WTRU may send the KNRP and nonce2 to the U2N Relay via Relay’s PKMF.

[0151] The U2N security procedure and related key hierarchy to enable multi-hop for U2N Relay may be enhanced as described herein. The PKMF / Remote WTRU and / or U2U Relay may be enhanced respectively to derive an intermediate fresh key ProSe Relay Key (PRK) from a multi-hop root credential MUP-PRUK and / or use PRK for PC5 link security establishment with the U2N Relay. An intermediate key may be used to prevent the propagation of the multi-hop root credential MUP-PRUK to a potentially high number of U2U Relays in the scenario where the Remote WTRU may need to send its MUP-PRUK to the U2U Relay for multi-hop U2N Relay connectivity. In that case, the MUP-PRUK may be exposed to a risk of leakage should any of the U2U Relays be compromised.

[0152] The use of a multi-hop specific root credential decoupled from the single-hop root credential occurs so that the PKMF may manage (e.g., revoke) authorization for multihop independently from single-hop. For example, MUP-PRUK may be provisioned with a different validity scope (e.g., VPLMN, time, and / or area) than UP-PRUK. PKMF may determine that the connection is multi-hop based on MUP-PRUK ID alone. The PKMF may leverage the MUP-PRUK ID multi-hop to preserve the existing protocol messages between the U2N Relay and PKMF. For example, PKMF may use that information fromthe MUP-PRUK ID (e.g., that connection request comes from a U2U Relay) to refrain from activating GBA push logic since the connected U2U Relay cannot support it (as it does not have access to the credential stored in the UICC of the Remote WTRU). The MUP-PRUK ID may include an indication (e.g., a flag) indicating that the related credential is specific to multi-hop U2N Relay connectivity.

[0153] FIG. 6 is a block diagram 600 illustrating an example PC5 key hierarchy for 5G ProSe U2N Relay security over the UP enhancements with a dedicated multi-hop root credential.

[0154] The Remote WTRU 602 may be provisioned with a multi-hop specific root credential MUP-PRUK 604 when indicating to its PKMF 606 that the Remote WTRU 602 wants to perform multi-hop U2N Relay connectivity. At 608, the Remote WTRU 602 may derive PRK 610 from MUP-PRUK 604 when establishing the security for the PC5 link with the U2U Relay 612. The Remote WTRU 602 may pass PRK 610 securely to the U2U Relay 612.

[0155] At 608, the PKMF 606 derives PRK 610 from MUP-PRUK 604 when requested by the U2N Relay 612. The U2N Relay may connect with a U2U Relay 612, based on the MUP-PRUK ID in the request identifying a multi-hop root credential.

[0156] At 614, the PKMF 606 may further derive KNRP 616 from PRK 610 and / or pass KNRP 616 to the U2N Relay 618.

[0157] At 614, the U2U Relay 618 may use the PRK 610 to generate a KNRP 616 during the PC5 link security establishment procedure with the U2N Relay 618. As an alternative to the key hierarchy above, the PKMF 606, Remote WTRU 602 using UP- PRUK, and / or subscription personal identifier (SUPI) of the Remote WTRU 602 may derive the MUP-PRUK 604 and / or MUP-PRUK ID. For example, the MUP-PRUK 604 and / or MUP-PRUK ID may be derived using the following key derivation function and / or parameters: MUP-PRUK = key derivation function (KDF) (UP-PRUK, SUPI of Remote WTRU 602, “multi-hop”) and / or MUP-PRUK ID = KDF (UP-PRUK, SUPI of Remote WTRU 602, “MUP-PRUK ID”).

[0158] For end-to-end security between the Remote WTRU and / or the U2N Relay or the network (e.g., N3IWF), application layer security mechanisms (e.g., using IPsec / IKEv2) may be used.

[0159] FIGs. 7A-7B are flow diagrams 700 that illustrate an example PC5 security establishment procedure for multi-hop 5G U2N Relay communications over the UP with enhancements for multi-hop. The procedure is illustrated with a single U2U Relay, but support for multiple U2U Relays may be possible with this solution.

[0160] As shown in FIG. 7A at 704a-c, the Remote WTRU, U2U Relay, and U2N Relay, respectively, are each provisioned with U2U / U2N Relay discovery and / or communication parameters by PCF, DDNMF, and / or PKMF. The Remote WTRU authorized for multi-hop discovery and / or communication may be provisioned with U2U Relay and / or U2N Relay discovery and / or communication parameters. The Remote WTRU and / or U2N Relay are provisioned with U2U_RSC and U2N_RSC. Each RSC may be associated with a multi-hop support indicator. The U2U Relay may be provisioned with U2U_RSC associated with a multi-hop support indicator.

[0161] At 708a, the Remote WTRU may send a ProSe Remote User Key request to its PKMF with an indication that the Remote WTRU wants to communicate with a U2N Relay via U2U Relay.

[0162] At 708b, the PKMF of the Remote WTRU may verify that the Remote WTRU may be authorized for U2N Relay services, including via multi-hop.

[0163] At 708c, if the Remote WTRU is authorized, the PKMF of the Remote WTRU may send a response including UP-PRUK, UP-PRUK ID and / or MUP-PRUK / MUP- PRUK ID to the Remote WTRU.

[0164] At 712, the Remote WTRU may discover the U2N Relay via the U2U Relay discovery messages. At 716, the Remote WTRU may send a DCR message to the U2U Relay, including the U2U_RSC, U2N_RSC, user info of U2N Relay, and / or MUP- PRUK ID.

[0165] At 720, the Remote WTRU and U2U Relay may perform mutual authentication using LTC. Additionally or alternatively, the Remote WTRU and / or U2U Relay may connect with network assistance (with U2U Relay in coverage) and / or skip mutual authentication. In that case, the Remote WTRU may pass an additional UP-PRUK ID associated with the U2U_RSC connectivity in the DCR message sent to the U2U Relay.

[0166] At 724a, the Remote WTRU may receive a DSM command message from the U2U Relay. The DSM command message may include conventional securityparameters (e.g., security policy and / or freshness parameters, etc.) to initiate the PC5 link security establishment.

[0167] At 724b, based on the Remote WTRU connecting to the U2N Relay via a U2U Relay, the Remote WTRU may derive a PRK from MUP-PRUK. The Remote WTRU may use as an input to the derivation function a noncel . The Remote WTRU may use U2U_RSC in the derivation as well to bind the PRK to a particular U2U Relay service.

[0168] At 724c, the Remote WTRU may send a DSM complete message to the U2U Relay, including PRK and / or noncel . The message may be fully protected (e.g., encrypted, integrity and / or replay) to avoid any potential exposure of PRK to an eavesdropper.

[0169] If more than one U2U Relay are involved, the intermediate U2U Relay may act as the Remote WTRU toward the next U2U Relay (except for the PRK derivation). Moreover, the intermediate U2U Relay may forward the PRK to the next U2U Relay in the chain.

[0170] At 728, the U2U Relay may send a DCR message to the U2N Relay, including MUP-PRUK ID, U2N_RSC, U2N user info, and / or noncel .

[0171] FIG. 7B is a continuation flow diagram 700b initially depicted in FIG. 7A. As shown in FIG. 7B at 732a, the U2N Relay may send a key request to the Remote WTRU PKMF via its PKMF. The request may include MUP-PRUK ID, U2N_RSC, and / or noncel . The Remote WTRU PKMF may be located for routing information in the MUP- PRUK ID.

[0172] At 732b, if U2U_RSC is used for PRK derivation as described at 724a-c, the U2U_RSC may be passed to the Remote WTRU PKMF via the U2N Relay and / or its PKMF. The PKMF may also use the U2U_RSC as an input parameter to the derivation of PRK.

[0173] At 732c, based on the presence of the U2U Relay indication, the Remote WTRU PKMF may derive a PRK from MUP-PRUK using noncel . The Remote WTRU PKMF also derives a KNRP from PRK using a nonce2.

[0174]

[0175] The PKMF may also use the presence of U2U Relay indication to not attempt the generation of a new UP-PRUK using the GBA PUSH mechanism. The PKMF maydetermine this knowing that the connecting U2U Relay cannot perform such a procedure which may require the Remote WTRU main network access credential (in the UICC). In case of the need to generate a new UP-PRUK, the PKMF may decide to reject the key request with an error code. The error code may indicate that a fresh UP- PRUK is required for multi-hop connectivity. The Remote WTRU may use such an error code to request a fresh UP-PRUK from its PKMF while in coverage and / or connect via a U2N Relay directly to generate a new one using GBA PUSH.

[0176] At 732d-e, the Remote WTRU PKMF may send the KNRP and / or the nonce2 to the U2N Relay via U2N Relay PKMF.

[0177] At 736a, the U2N Relay may send an integrity protected DSM Command message to the U2U Relay, including nonce2. At 736b, the U2U Relay may derive KNRP from PRK using nonce2. The U2U Relay may derive a session key and / or security keys. The U2U Relay may verify the security of the DSM command with the generated security keys. The U2U Relay may determine that both the Remote WTRU and / or U2N Relay may be authorized for multi-hop U2N Relay connectivity if the verification is successful. At 736c, the U2U Relay may send a protected (e.g., for confidentiality and / or integrity) DSM complete message to the U2N Relay. At 736d, the U2N Relay may verify the security of the DSM command with the generated security keys. The U2N Relay may determine that both the Remote WTRU and / or the U2U Relay are authorized for multi-hop U2N Relay connectivity if the verification is successful.

[0178] At 740a, the U2N Relay may sense a DCA message to the U2U Relay confirming a successful relayed connection. At 740b, the U2N Relay may provide 5GC with MUP- PRUK ID during a Remote WTRU Report procedure to identify the Remote WTRU using the multi-hop U2N Relay connectivity service. At 740c, the U2U Relay may send a DCA message to the Remote WTRU confirming a successful multi-hop relayed connection.

[0179] In FIGs. 7A-7B, the key hierarchy and / or procedures may be illustrated using the UP approach and / or an MUP-PRUK. The solution also applies equally using the CP approach with the following differences. Instead of MUP-PRUK, the Remote WTRU may use an MCP-PRUK and / or MCP-PRUK ID that the Remote WTRU possesses (from a previous connection with the U2N Relay). The MCP-PRUK / MCP-PRUK ID maybe established by both Remote WTRU and / or ALISF at the same time (e.g., automatically) when establishing CP-PRUK / CP-PRUK ID during a single-hop connection with a U2N Relay. On the network side, PRK may be derived from MCP- PRUK by AUSF instead of PKMF.

Claims

CLAIMSWhat is claimed is:1 . A wireless transmit / receive unit WTRU comprising: a processor configured to: receive a request from a remote WTRU to establish a multi-hop WTRU-to- network (U2N) connection between the remote WTRU and a network relay WTRU; send a first security mode command message to the remote WTRU to establish secure communications with the remote WTRU over a direct sidelink interface between the WTRU and the remote WTRU; receive a first security mode complete message from the remote WTRU, wherein the first security mode complete message comprises a ProSe relay key (PRK) and a noncel , wherein the PRK is based on a user plane ProSe remote user key (UP-PRUK) of the remote WTRU; sends a communication request message to the network relay WTRU; receive a second security mode command message from the network relay WTRU; determine a key new radio ProSe (KNRP) based at least on the PRK to authorize the remote WTRU and network relay WTRU for the multi-hop network relay WTRU connection; send second a security mode complete message to the network relay WTRU; and send an accept message to the remote WTRU.

2. The WTRU of claim 1 , wherein the request comprises a relay service code (RSC) associated with the WTRU, an RSC associated with the network relay WTRU, and an UP-PRUK ID.

3. The WTRU of claim 2, wherein the processor is configured to: receive discovery and communication parameters from a direct discovery name management function (DDNMF), policy control function (PCF), or a ProSe keymanagement function (PKMF), wherein the discovery and communication parameters comprise a multi-hop support indicator for establishing multi-hop connections.

4. The WTRU of claim 1 , wherein the processor is configured to: perform mutual authentication with the remote WTRU using a long term credential (LTC).

5. The WTRU of claim 4, wherein the processor is configured to: perform mutual authentication with the remote WTRU prior to sending the security mode message.

6. The WTRU of claim 1 , wherein the communication request message comprises one or more of a relay service code (RSC) associated with the network relay WTRU, a nonce2, or a first UP-PRUK ID.

7. The WTRU of claim 6, wherein the communication request message further comprises one or more of a second UP-PRUK ID, the second UP-PRUK ID associated with the network relay WTRU, wherein the second UP-PRUK ID is to establish the multi-hop U2N connection without network assistance.

8. The WTRU of claim 1 , wherein the processor is configured to: receive the accept message from the network relay WTRU prior to sending the accept message to the remote WTRU.

9. The WTRU of claim 1 , wherein the PRK is further based on a relay service code (RSC) associated with the WTRU.

10. The WTRU of claim 1 , wherein the PRK is further based on a control plane ProSe remote user key (CP-PRUK) of the remote WTRU.

11. A method performed by a wireless transmit / receive unit (WTRU), the method comprising: receiving a request from a remote WTRU to establish a multi-hop WTRU-to- network (U2N) connection between the remote WTRU and a network relay WTRU; sending a first security command mode message to the remote WTRU to establish secure communications with the remote WTRU over a direct sidelink interface between the WTRU and the remote WTRU; receiving a first security mode complete message from the remote WTRU, wherein the first security mode complete message comprises a ProSe relay key (PRK) and noncel , wherein the PRK is based on a user plane ProSe remote user key (UP- PRUK) of the remote WTRU; sending a communication request message to the network relay WTRU; receiving a second security mode message from the network relay WTRU; determining a key new radio ProSe (KNRP) based at least on the PRK to authorize the remote WTRU and network relay WTRU for the multi-hop network relay WTRU connection; sending a second security mode complete message to the network relay WTRU; and sending an accept message to the remote WTRU.

12. The method of claim 11 , wherein the request comprises a relay service code (RSC) associated with the WTRU, an RSC associated with the network relay WTRU, and an UP-PRUK ID.

13. The method of claim 12, further comprising: receiving discovery and communication parameters from a direct discovery name management function (DDNMF), policy control function (PCF), or a ProSe key management function (PKMF), wherein the discovery and communication parameters comprise a multi-hop support indicator for establishing multi-hop connections.

14. The method of claim 11 , further comprising: performing mutual authentication with the remote WTRU using a long term credential (LTC).

15. The method of claim 14, further comprising: performing mutual authentication with the remote WTRU prior to sending the security mode message.

16. The method of claim 11 , wherein the communication request message comprises one or more of a relay service code (RSC) associated with the network relay WTRU, a nonce2, or a first UP-PRUK ID.

17. The method of claim 16, wherein the communication request message comprises a second UP-PRUK ID, the second UP-PRUK ID associated with the network relay WTRU connectivity to establish the multi-hop U2N connection without network assistance.

18. The method of claim 11 , further comprising: receiving the accept message from the network relay WTRU prior to sending the accept message to the remote WTRU.

19. The method of claim 11 , wherein the PRK is further based on a relay service code (RSC) associated with the WTRU.

20. The method of claim 11 , wherein the PRK is further based on a control plane ProSe remote user key (CP-PRUK) of the remote WTRU.

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