Handling connection rejection via U2U relay associated with backoff time instead of source-end WTRU

Abstract

Systems and methods are provided for handling connection rejections via a wireless transmit / receive unit (WTRU)-WTRU (U2U) relay associated with a backoff time on behalf of a source-end WTRU. For example, a relay WTRU may retry establishing a connection with a target WTRU on behalf of a source WTRU based on receiving a rejection (e.g., with a backoff value) from the target WTRU. The source WTRU may associate a rejection message with the target WTRU, and the relay WTRU may be available to reach other target WTRUs. The relay WTRU may send rejection messages to other source WTRUs for the same target WTRU (e.g., if a backoff duration is active and running).

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of U.S. Provisional Patent Application No. 63 / 457,616, filed April 6, 2023, the contents of which are incorporated herein by reference in their entirety. [Background technology]

[0002] Mobile communications using radio communications continues to evolve. The fifth generation is sometimes referred to as 5G. Previous (traditional) generations of mobile communications may be, for example, fourth generation (4G) long term evolution (LTE). Summary of the Invention

[0003] Systems and methods are described herein for handling connection rejections on behalf of a source-end WTRU via a wireless transmit / receive unit (WTRU)-WTRU (U2U) relay associated with a backoff time. The relay WTRU may retry establishing a connection with a target WTRU on behalf of the source WTRU, for example, based on receiving a rejection (e.g., with a backoff value) from the target WTRU. The source WTRU may associate a rejection message with the target WTRU, and the relay WTRU may be available to reach other target WTRUs. The relay WTRU may send rejection messages to other source WTRUs for the same target WTRU (e.g., if a backoff duration is active and running).

[0004] The relay WTRU may retry establishing a connection with the target WTRU on behalf of the source WTRU. For example, the relay WTRU may receive a first rejection message from the target WTRU. The first rejection message may be associated with a first direct communication request (DCR) transmission or a first link modification request (LMR) transmission. The first rejection message may indicate congestion. The first rejection message may indicate a rejection cause value. The first rejection message may indicate a backoff value. The first DCR or first LMR may be associated with the source WTRU. The relay WTRU may determine a number of retransmissions associated with the source WTRU (e.g., the number of retransmissions associated with the request to establish a connection). The WTRU may send a second rejection message to the source WTRU. The second rejection message may be sent based on whether the number of retransmissions associated with the source WTRU is less than a threshold (e.g., a maximum number of allowed retransmissions). The second rejection message to the source WTRU may indicate whether the relay WTRU will make (e.g., attempt) one or more retransmission attempts on behalf of the source WTRU. The second rejection message may indicate the number of retransmission attempts.

[0005] For example, if the number of retransmission attempts associated with the source WTRU is less than a threshold, the relay WTRU performs one or more of the following: The relay WTRU may track a duration associated with a back-off value (e.g., indicated by the first rejection message). The relay WTRU may include an indication in the second rejection message to the source WTRU that the relay WTRU will (e.g., attempt) a retransmission attempt on behalf of the source WTRU. The relay WTRU may send a second DCR / LMR transmission to the target WTRU on behalf of the source WTRU (e.g., based on a determination that the back-off value has elapsed). For example, if the number of retransmission attempts is greater than or equal to a threshold, the relay WTRU may decide to abort the direct link establishment. The second rejection message may indicate an identity associated with the target WTRU. The second rejection message may indicate that the maximum number of retries has been reached.

[0006] The relay WTRU may send a rejection message to the source WTRU without attempting to establish a connection with the target WTRU, for example, if the relay WTRU has already received a rejection for a source WTRU different from the target WTRU. The WTRU may receive a first message from the target WTRU. The first message may indicate a rejection associated with a first request to establish a first connection between the first source WTRU and the target WTRU. The first message may indicate a back-off value associated with the target WTRU. The relay WTRU may receive a second message from a second source WTRU. The second message may be associated with a second request to establish a second connection between the second source WTRU and the target WTRU using the relay WTRU. The relay WTRU may send a third message to the second source WTRU indicating that the target WTRU rejected the first request to establish the first connection between the first source WTRU and the target WTRU. The third message may indicate a cause value (e.g., indicating that the target WTRU previously rejected a request to establish a first connection between the first source WTRU and the target WTRU). The relay WTRU may, for example, send the third message without attempting to establish with the target WTRU (e.g., because the relay WTRU has already received rejections for the first source WTRU and the target WTRU). The relay WTRU may determine that a duration associated with the backoff value has expired. The WTRU may send a fourth message to the target WTRU (e.g., based on the determination that a duration associated with the backoff value has expired). The fourth message may be associated with one or more of the first request to establish a first connection between the first source WTRU and the target WTRU or the second request to establish a second connection between the second source WTRU and the target WTRU. The fourth message may be sent based on, for example, a determination that the number of retransmissions associated with establishing a connection with the target WTRU is less than a threshold.The relay WTRU may determine the number of retransmissions. The relay WTRU may receive a fifth message from the target WTRU indicating that the second request to establish a second connection between the second source WTRU and the target WTRU is rejected. The relay WTRU may determine (e.g., based on the fifth message) that the number of retransmissions associated with the connection establishment with the target WTRU is greater than or equal to a threshold. The relay WTRU may send a rejection message to the second source WTRU associated with the pending link establishment connection request (e.g., based on the determination that the number of retransmissions associated with the connection establishment with the target WTRU is greater than or equal to a threshold).

[0007] The WTRU may send a connection establishment request to the target WTRU. The connection establishment request may be a DCR or an LMR. The WTRU may receive a back-off value associated with a connection establishment rejection associated with the target WTRU. The back-off value associated with the connection establishment rejection may be received in response to the transmitted connection establishment request. The WTRU may receive a first message indicating that the WTRU should retry establishing a connection with the target WTRU. The first message may indicate a value associated with a waiting period duration. The WTRU may track a duration associated with the back-off value. Tracking the duration may be started based on receiving a third message from the target WTRU. Tracking the duration may be started based on a determination that the waiting period duration has expired. The WTRU may decide to retry establishing a connection with the target WTRU. The decision to retry establishing a connection with the target WTRU may be based on receiving a third message from the target WTRU indicating to retry establishing the connection. The decision to retry establishing a connection with the target WTRU may be based on a determination that the duration associated with the back-off value has expired. In one example, the WTRU may be a relay WTRU. In the case of a relay WTRU, the connection establishment rejection may be associated with the first source WTRU. The relay WTRU may send a message to the source WTRU indicating that the target WTRU has requested to wait (e.g., based on receiving the rejection message). The relay WTRU may attempt to establish a connection between the source WTRU and the target WTRU. [Brief explanation of the drawings]

[0008] [Figure 1A] FIG. 1 is a system diagram illustrating an example communication system in which one or more disclosed embodiments may be implemented. [Figure 1B]1B is a system diagram illustrating an exemplary wireless transmit / receive unit (WTRU) that may be used within the communication system illustrated in FIG. 1A, according to one embodiment. [Figure 1C] 1A is a system diagram illustrating an example radio access network (RAN) and an example core network (CN) that may be used within the communication system illustrated in FIG. 1A, according to one embodiment. [Figure 1D] 1B is a system diagram illustrating a further exemplary RAN and a further exemplary CN that may be used within the communication system illustrated in FIG. 1A, according to one embodiment. [Figure 2] 10 illustrates an example ProSe communication via a ProSe Layer 3 inter-WTRU relay. [Figure 3] 10 illustrates an exemplary ProSe communication via an exemplary ProSe Layer 2 inter-WTRU relay. [Figure 4] 10 shows an example flow that enables a U2U relay to process a DC / LM reject message and retry on behalf of a source WTRU. [Figure 5] 10 shows an example flow that enables a source WTRU to be notified of a target WTRU's request rejection and the cause thereof. [Figure 6] 10 shows an example flow that may allow a U2U relay to process multiple requests to the same target WTRU if the target WTRU has previously rejected the request. DETAILED DESCRIPTION OF THE INVENTION

[0009] 1A is a diagram illustrating an example communication system 100 in which one or more disclosed embodiments may be implemented. Communication system 100 may be a multiple-access system that provides content, such as voice, data, video, messaging, broadcasts, etc., to multiple wireless users. Communication system 100 may enable multiple wireless users to access such content through sharing of system resources, including wireless bandwidth. For example, the communication system 100 may use 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), etc.

[0010] 1A, communications system 100 may include wireless transmit / receive units (WTRUs) 102a, 102b, 102c, 102d, RANs 104 / 113, CNs 106 / 115, public switched telephone network (PSTN) 108, the Internet 110, and other networks 112, although it will be understood that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and / or network elements. Each of 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 "STA," may be configured to transmit and / or receive wireless signals and may include user equipment (UE), mobile stations, fixed or mobile subscriber units, subscription-based units, pagers, mobile phones, personal digital assistants (PDAs), smartphones, laptops, netbooks, personal computers, wireless sensors, hotspots or Mi-Fi devices, Internet of Things (ioT) devices, watches or other wearable, head-mounted displays (HMDs), vehicles, drones, medical devices and applications (e.g., for remote surgery), industrial devices and applications (e.g., robots and / or other wireless devices operating in industrial and / or automated processing chain contexts), consumer electronics devices, devices operating on commercial and / or industrial wireless networks, etc. Any of the WTRUs 102a, 102b, 102c, and 102d may be referred to interchangeably as a UE.

[0011] The communications system 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 communications networks, such as the CN 106 / 115, the Internet 110, and / or other networks 112. By way of example, the base stations 114a, 114b may be a base transceiver station (BTS), a Node-B, an eNodeB (eNB), a Home Node B, a Home eNodeB, a gNode B (gNB), an NR NodeB, a site controller, an access point (AP), a wireless router, etc. Although the base stations 114a, 114b are each depicted as a single element, it will be understood that the base stations 114a, 114b may include any number of interconnected base stations and / or network elements.

[0012] 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 station controller (BSC), a radio network controller (RNC), a relay node, etc. The base station 114a and / or base station 114b may be configured to transmit and / or receive radio signals on one or more carrier frequencies, which may be referred to as a cell (not shown). These frequencies may be licensed spectrum, unlicensed spectrum, or a combination of licensed and unlicensed spectrum. A cell may provide wireless service coverage for a particular geographic area, which may be relatively fixed or may change over time. A cell may be further 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 transceiver for each sector of the cell. In one embodiment, the base station 114a may employ multiple-input multiple output (MIMO) technology and may utilize multiple transceivers per sector of the cell, for example, using beamforming to transmit and / or receive signals in desired spatial directions.

[0013] 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).

[0014] More specifically, as noted above, the communications system 100 may be a multiple-access system, but may use one or more channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, etc. For example, the base station 114 a and the WTRUs 102 a, 102 b, 102 c in the RAN 104 / 113 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 communications 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 ​​Uplink Packet Access (HSUPA).

[0015] In one 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).

[0016] In one embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as New Radio (NR) radio access, which may establish the air interface 116 using NR technology.

[0017] In one 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 jointly implement LTE radio access and NR radio access, e.g., using dual connectivity (DC) principles. Thus, the air interface utilized by the WTRUs 102a, 102b, 102c may be characterized by multiple types of radio access technologies and / or transmissions sent to and from multiple types of base stations (e.g., eNBs and gNBs).

[0018] In other embodiments, the base station 114a and the WTRUs 102a, 102b, 102c may implement a wireless technology 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), or the like.

[0019] 1A may be, for example, a wireless router, a Home NodeB, a Home eNodeB, or an access point and may utilize any suitable RAT to facilitate wireless connectivity in a local area such as a business, a home, a vehicle, a campus, an industrial facility, an air corridor (e.g., for use by drones), a road, etc. 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 one 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. 1A, the base station 114b may have a direct connection to the Internet 110. Therefore, the base station 114b may not need to access the Internet 110 through the CN 106 / 115.

[0020] The RAN 104 / 113 may communicate with the CN 106 / 115, which may be any type of network configured to provide voice, data, application, and / or voice over internet protocol (VoIP) services to one or more of the WTRUs 102a, 102b, 102c, 102d. The data may have various quality of service (QoS) requirements, such as different throughput, latency, error tolerance, reliability, data throughput, and mobility requirements. The CN 106 / 115 may provide call control, billing services, mobile location-based services, prepaid calling, Internet connectivity, video distribution, and / or perform high-level security functions such as user authentication. Although not shown in FIG. 1A , it will be understood that the RAN 104 / 113 and / or the CN 106 / 115 may communicate directly or indirectly with other RANs employing 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 utilize NR radio technology, the CN 106 / 115 may also communicate with another RAN (not shown) using GSM, UMTS, CDMA2000, WiMAX, E-UTRA, or WiFi radio technology.

[0021] 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 other networks 112. The PSTN 108 may include a circuit-switched telephone network providing 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), the user datagram protocol (UDP), and / or the internet protocol (IP) of the TCP / IP Internet protocol suite. The network 112 may include wired and / or wireless communication networks owned and / or operated by other service providers. For example, the network 112 may include another CN connected to one or more RANs, which may use the same RAT as the RAN 104 / 113 or a different RAT.

[0022] 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 wireless networks over different wireless links.) For example, the WTRU 102c shown in FIG. 1A may be configured to communicate with a base station 114a, which may employ a cellular-based wireless technology, and a base station 114b, which may employ an IEEE 802.2 wireless technology.

[0023] 1B is a system diagram illustrating an example WTRU 102. As shown in FIG. 1B, the WTRU 102 may include, among other things, 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. It will be understood that the WTRU 102 may include any sub-combination of the foregoing elements while remaining consistent with an embodiment.

[0024] The processor 118 may be a general-purpose processor, a special-purpose processor, a conventional processor, a digital signal processor (DSP), multiple microprocessors, one or more microprocessors associated with a DSP core, a controller, a microcontroller, an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) circuit, any other type of integrated circuit (IC), a state machine, etc. 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. 1B depicts the processor 118 and the transceiver 120 as separate components, it will be understood that the processor 118 and the transceiver 120 may be integrated together in an electronic package or chip.

[0025] The transmit / receive element 122 may be configured to transmit or receive signals to or from a base station (e.g., 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 one 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 and light signals. It will be understood that the transmit / receive element 122 may be configured to transmit and / or receive any combination of wireless signals.

[0026] 1B 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.

[0027] The transceiver 120 may be configured to modulate signals transmitted by the transmit / receive element 122 and demodulate signals 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 to enable the WTRU 102 to communicate via multiple RATs, such as, for example, NR and IEEE 802.11.

[0028] The processor 118 of the WTRU 102 may be coupled to and may receive user-entered data from a speaker / microphone 124, a keypad 126, and / or a display / touchpad 128 (e.g., a liquid crystal display (LCD) display unit or an organic light-emitting 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. Additionally, the processor 118 may access information from and store data in any type of suitable memory, such as non-removable memory 130 and / or removable memory 132. The non-removable memory 130 may include random-access memory (RAM), read-only 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, etc. 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 home computer (not shown).

[0029] The processor 118 may receive power from the power source 134 and may be configured to distribute and / or control the power to other components in the WTRU 102. The power source 134 may be any suitable device for providing power to the WTRU 102. For example, the power source 134 may include one or more dry batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, etc.

[0030] The processor 118 may also be coupled to a 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 instead of, information from the GPS chipset 136, the WTRU 102 may receive location information from base stations (e.g., base stations 114a, 114b) over the air interface 116 and / or determine its location based on the timing of signals received from two or more nearby base stations. It will be appreciated that the WTRU 102 may obtain location information by way of any suitable location-determination method while remaining consistent with an embodiment.

[0031] 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 electronic compass, a satellite transceiver, a digital camera (for photos and / or videos), 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, etc. The peripheral device 138 may include one or more sensors, which may be one or more of a gyroscope, an accelerometer, a Hall effect sensor, a magnetometer, a direction 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.

[0032] The WTRU 102 may include a full-duplex radio where transmission and reception of some or all of the signals associated with a particular subframe (e.g., for both the UL (e.g., for transmission) and downlink (e.g., for reception)) may be parallel and / or simultaneous. The full-duplex radio may include an interference management unit to reduce and or substantially eliminate self-interference through either hardware (e.g., a choke) or signal processing via a processor (e.g., via a separate processor (not shown) or processor 118). In one embodiment, the WTRU 102 may include a half-duplex radio for transmission and reception of either some or all of the signals (e.g., associated with a particular subframe for either the UL (e.g., for transmission) or downlink (e.g., for reception)).

[0033] 1C is a system diagram illustrating the RAN 104 and the CN 106, according to one embodiment. As mentioned above, the RAN 104 may employ E-UTRA radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 104 may also communicate with the CN 106.

[0034] The RAN 104 may include eNodeBs 160a, 160b, and 160c, although it will be understood that the RAN 104 may include any number of eNodeBs while remaining consistent with an embodiment. The eNodeBs 160a, 160b, and 160c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, and 102c over the air interface 116. In an embodiment, the eNodeBs 160a, 160b, and 160c may implement MIMO technology. Thus, the eNodeB 160a may, for example, use multiple antennas to transmit wireless signals to and / or receive wireless signals from the WTRU 102a.

[0035] Each of the eNodeBs 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, etc. As shown in FIG. 1C, the eNodeBs 160a, 160b, 160c may communicate with one another via an X2 interface.

[0036] 1C may include a mobility management entity (MME) 162, a serving gateway (SGW) 164, and a packet data network (PDN) gateway (or PGW) 166. Although each of the foregoing elements is depicted as part of the CN 106, it will be understood that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0037] The MME 162 may be connected to each of the eNode-Bs 160a, 160b, 160c in the RAN 104 via an S1 interface and may function as a control node. For example, the MME 162 may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, activating / deactivating bearers, selecting a particular serving gateway during initial attach of the WTRUs 102a, 102b, 102c, etc. The MME 162 may provide a control plane function for switching between the RAN 104 and other RANs (not shown) that employ other radio technologies such as GSM and / or WCDMA.

[0038] The SGW 164 may be connected to each of the eNodeBs 160a, 160b, 160c in the RAN 104 via an S1 interface. The SGW 164 may generally route and forward user data packets to and from the WTRUs 102a, 102b, 102c. The SGW 164 may perform other functions, such as anchoring the user plane during inter-eNodeB handover, triggering paging when DL data is available to the WTRUs 102a, 102b, 102c, and managing and storing the context of the WTRUs 102a, 102b, 102c.

[0039] The SGW 164 may be connected to a PGW 166, which may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communication between the WTRUs 102a, 102b, 102c and IP-enabled devices.

[0040] The CN 106 may facilitate communications with other networks. For example, the CN 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 landline communications devices. For example, the CN 106 may include or communicate with an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that acts 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 other networks 112, which may include other wired and / or wireless networks owned and / or operated by other service providers.

[0041] Although the WTRU is illustrated in FIGS. 1A-1D as a wireless terminal, it is contemplated that in certain representative embodiments, such a terminal may use a wired communication interface (e.g., temporarily or permanently) with the communication network.

[0042] In a representative embodiment, the other network 112 may be a WLAN.

[0043] A WLAN in infrastructure basic service set (BSS) mode may have an access point (AP) of the BSS and one or more stations (STAs) associated with the AP. The AP may have access or interface to a distribution system (DS) or another type of wired / wireless network that carries traffic into and / or out of the BSS. Traffic originating outside the BSS to a STA may arrive through the AP and be sent to the STA. Traffic originating at a STA and destined for a destination outside the BSS may be sent to the AP to be sent to the respective destination. Traffic between STAs within a BSS may be sent through the AP, for example, where the source STA may send traffic to the AP, and the AP may send traffic to the destination STA. Traffic between STAs within a BSS may be considered and / or referred to as peer-to-peer traffic. Peer-to-peer traffic may be sent between (e.g., directly between) a source STA and a destination STA using a direct link setup (DLS). In certain representative embodiments, the DLS may use 802.11e DLS or 802.11z tunneled DLS (TDLS). A WLAN using an Independent BSS (IBSS) mode may not have an AP, and STAs within or using the IBSS (e.g., all of the STAs) may communicate directly with each other. The IBSS mode of communication may be referred to herein as an "ad hoc" communication mode.

[0044] When using the 802.11ac infrastructure mode of operation or a similar mode of operation, an AP may transmit beacons on a fixed channel, such as a primary channel. The primary channel may be a fixed width (e.g., a 20 MHz wide bandwidth) or a width that is dynamically configured via signaling. The primary channel may be the operating channel of the BSS, but may also be used by STAs to establish a connection with the AP. In certain representative embodiments, for example, in an 802.11 system, Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA) may be implemented. With CSMA / CA, STAs (e.g., all STAs), 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 in a given BSS at any given time.

[0045] High Throughput (HT) STAs may use 40 MHz wide channels for communication, which may be formed, for example, through a combination of a primary 20 MHz channel and adjacent or non-adjacent 20 MHz channels.

[0046] A Very High Throughput (VHT) STA may support channels with widths of 20 MHz, 40 MHz, 80 MHz, and / or 160 MHz. A 40 MHz and / or 80 MHz channel may be formed by combining adjacent 20 MHz channels. A 160 MHz channel may be formed by combining eight contiguous 20 MHz channels or by combining two non-adjacent 80 MHz channels, which may be referred to as an 80+80 configuration. For the 80+80 configuration, after channel encoding, the data may pass through a segment parser that may separate the data into two streams. Inverse Fast Fourier Transform (IFFT) processing and time-domain processing may be performed separately on each stream. The streams may be mapped to two 80 MHz channels, and the data may be transmitted by the transmitting STA. At the receiver of the receiving STA, the operations described above for the 80+80 configuration may be reversed, and the combined data may be sent to Medium Access Control (MAC).

[0047] Sub-1 GHz operating modes are supported by 802.11af and 802.11ah. Channel operating bandwidths and carriers are reduced in 802.11af and 802.11ah compared to those used in 802.11n and 802.11ac. 802.11af supports 5 MHz, 10 MHz, and 20 MHz bandwidths in the TV White Space (TVWS) spectrum, while 802.11ah supports 1 MHz, 2 MHz, 4 MHz, 8 MHz, and 16 MHz bandwidths using non-TVWS spectrum. According to representative embodiments, 802.11ah may support meter-type control / machine-type communications, such as MTC devices within macro coverage areas. MTC devices may have limited capabilities, including support for (e.g., only) certain and / or limited bandwidths. MTC devices may include batteries with above-threshold battery life (e.g., to maintain very long battery life).

[0048] WLAN systems that can support multiple channels and channel bandwidths, such as 802.11n, 802.11ac, 802.11af, and 802.11ah, include a channel that can be designated as a primary channel. The primary channel can have a bandwidth equal to the maximum common operating bandwidth supported by all STAs in the BSS. The bandwidth of the primary channel can be configured and / or limited by the STAs among all STAs operating in the BSS that support the minimum bandwidth operating mode. In an 802.11ah embodiment, the primary channel can be 1 MHz wide for STAs (e.g., MTC-type devices) that support (e.g., only) the 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) configuration can depend on the status of the primary channel. For example, if the primary channel is active due to a STA (that only supports 1 MHz mode of operation) transmitting to the AP, the entire available frequency band may be considered active, even though most of the frequency band may remain inactive and available.

[0049] In the United States, the available frequency band that can be used by 802.11ah is 902MHz to 928MHz. In South Korea, the available frequency band is 917.5MHz to 923.5MHz. In Japan, the available frequency band is 916.5MHz to 927.5MHz. The total bandwidth available for 802.11ah is 6MHz to 26MHz depending on the country code.

[0050] 1D is a system diagram illustrating the RAN 113 and the CN 115, according to one embodiment. As noted above, the RAN 113 may employ NR radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 113 may also communicate with the CN 115.

[0051] The RAN 113 may include gNBs 180a, 180b, and 180c, although it will be understood that the RAN 113 may include any number of gNBs while remaining consistent with an embodiment. The gNBs 180a, 180b, and 180c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, and 102c over the air interface 116. In an embodiment, the gNBs 180a, 180b, and 180c may implement MIMO technology. For example, the gNB 180a, 180b may transmit signals to and / or receive signals from the gNBs 180a, 180b, and 180c using beamforming. Thus, the gNB 180a may transmit and / or receive wireless signals to and / or from the WTRU 102a using, for example, multiple antennas. In one 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 one embodiment, the gNBs 180a, 180b, 180c may implement Coordinated Multi-Point (CoMP) technology. For example, the WTRU 102a may receive coordinated transmissions from the gNBs 180a and 180b (and / or 180c).

[0052] The WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c using transmissions associated with 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 the gNBs 180a, 180b, 180c using subframes or transmission time intervals (TTIs) of different or scalable lengths (e.g., including different numbers of OFDM symbols and / or lasting different lengths of absolute time).

[0053] 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 a standalone configuration, the WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c without accessing another RAN (e.g., eNodeBs 160a, 160b, 160c, etc.). In a standalone configuration, the WTRUs 102a, 102b, 102c may utilize one or more of the gNBs 180a, 180b, 180c as mobility anchor points. In a standalone configuration, the WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c using signals in unlicensed bands. In a non-standalone configuration, the WTRUs 102a, 102b, 102c may communicate with and connect to gNBs 180a, 180b, 180c while also communicating with and connecting to another RAN, such as eNodeBs 160a, 160b, 160c. For example, the WTRUs 102a, 102b, 102c may implement DC principles to communicate with one or more gNBs 180a, 180b, 180c and one or more eNodeBs 160a, 160b, 160c substantially simultaneously. In a non-standalone configuration, the eNodeBs 160a, 160b, 160c may act as mobility anchors for the WTRUs 102a, 102b, 102c, and the gNBs 180a, 180b, 180c may provide additional coverage and / or throughput for serving the WTRUs 102a, 102b, 102c.

[0054] 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 for network slicing, dual connectivity, interworking between NR and E-UTRA, routing of user plane data to User Plane Functions (UPFs) 184a, 184b, routing of control plane information to Access and Mobility Management Functions (AMFs) 182a, 182b, etc. As shown in FIG. 1D , the gNBs 180a, 180b, 180c may communicate with each other via an Xn interface.

[0055] 1D 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 foregoing elements is depicted as part of the CN 115, it will be understood that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0056] 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 function as a control node. For example, the AMF 182a, 182b may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, supporting network slicing (e.g., handling different PDU sessions with different requirements), selecting a particular SMF 183a, 183b, managing registration areas, terminating NAS signaling, mobility management, etc. Network slicing may be used by the AMF 182a, 182b to customize the CN support of the WTRUs 102a, 102b, 102c based on the type of service utilizing the 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, etc. 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.

[0057] The SMFs 183a and 183b may be connected to the AMFs 182a and 182b in the CN 115 via an N11 interface. The SMFs 183a and 183b may also be connected to the UPFs 184a and 184b in the CN 115 via an N4 interface. The SMFs 183a and 183b may select and control the UPFs 184a and 184b and configure the routing of traffic through the UPFs 184a and 184b. The SMFs 183a and 183b may perform other functions, such as managing and allocating UE IP addresses, managing PDU sessions, controlling policy enforcement and QoS, and providing downlink data notification. PDU session types may be IP-based, non-IP-based, Ethernet-based, etc.

[0058] The UPFs 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 UPFs 184, 184b may perform other functions such as routing and forwarding packets, enforcing user plane policy, supporting multi-homed PDU sessions, handling user plane QoS, buffering downlink packets, providing mobility anchoring, etc.

[0059] The CN 115 may facilitate communication with other networks. For example, the CN 115 may include or communicate with an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that acts 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 other networks 112, which may include other wired and / or wireless networks owned and / or operated by other service providers. In one embodiment, the WTRUs 102a, 102b, 102c may be connected to local data networks (DNs) 185a, 185b through the UPFs 184a, 184b via an N3 interface to the UPFs 184a, 184b and an N6 interface between the UPFs 184a, 184b and the DNs 185a, 185b.

[0060] 1A-1D and the corresponding description thereof, one or more or all of the functions described herein with respect to one or more of the WTRUs 102a-102d, base stations 114a-114b, eNodeBs 160a-160c, MME 162, SGW 164, PGW 166, gNBs 180a-180c, AMFs 182a-182b, UPFs 184a-184b, SMFs 183a-183b, DNs 185a-185b, and / or any other devices 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 simulate network and / or WTRU functions.

[0061] The emulation devices may be designed to implement one or more tests of other devices in a lab environment and / or an operator network environment. For example, one or more emulation devices may perform one or more or all functions while fully or partially implemented and / or deployed as part of a wired and / or wireless communication network to test other devices in the communication network. One or more emulation devices may perform one or more or all functions while temporarily implemented / deployed as part of a wired and / or wireless communication network. The emulation devices may be directly coupled to another device for testing purposes and / or may perform the tests using terrestrial wireless communication.

[0062] One or more emulation devices may perform one or more functions, inclusive, while not being implemented / deployed as part of a wired and / or wireless communication network. For example, the emulation devices may be utilized in test scenarios in a test lab and / or in an undeployed (e.g., test) wired and / or wireless communication network to implement testing of one or more components. One or more emulation devices may be test equipment. Direct RF coupling and / or wireless communication via RF circuitry (which may include, e.g., one or more antennas) may be used by the emulation devices to transmit and / or receive data.

[0063] Systems and methods are described herein for handling connection rejections on behalf of a source-end WTRU via a wireless transmit / receive unit (WTRU)-WTRU (U2U) relay associated with a backoff time. The relay WTRU may retry establishing a connection with a target WTRU on behalf of the source WTRU, for example, based on receiving a rejection (e.g., with a backoff value) from the target WTRU. The source WTRU may associate a rejection message with the target WTRU, and the relay WTRU may be available to reach other target WTRUs. The relay WTRU may send rejection messages to other source WTRUs for the same target WTRU (e.g., if a backoff duration is active and running).

[0064] The relay WTRU may retry establishing a connection with the target WTRU on behalf of the source WTRU. For example, the relay WTRU may receive a first rejection message from the target WTRU. The first rejection message may be associated with a first direct communication request (DCR) transmission or a first link modification request (LMR) transmission. The first rejection message may indicate congestion. The first rejection message may indicate a rejection cause value. The first rejection message may indicate a backoff value. The first DCR or first LMR may be associated with the source WTRU. The relay WTRU may determine a number of retransmissions associated with the source WTRU (e.g., the number of retransmissions associated with the request to establish a connection). The WTRU may send a second rejection message to the source WTRU. The second rejection message may be sent based on whether the number of retransmissions associated with the source WTRU is less than a threshold (e.g., a maximum number of allowed retransmissions). The second rejection message to the source WTRU may indicate whether the relay WTRU will make (e.g., attempt) one or more retransmission attempts on behalf of the source WTRU. The second rejection message may indicate the number of retransmission attempts.

[0065] For example, if the number of retransmission attempts associated with the source WTRU is less than a threshold, the relay WTRU performs one or more of the following: The relay WTRU may track a duration associated with a back-off value (e.g., indicated by the first rejection message). The relay WTRU may include an indication in the second rejection message to the source WTRU that the relay WTRU will (e.g., attempt) a retransmission attempt on behalf of the source WTRU. The relay WTRU may send a second DCR / LMR transmission to the target WTRU on behalf of the source WTRU (e.g., based on a determination that the back-off value has elapsed). For example, if the number of retransmission attempts is greater than or equal to a threshold, the relay WTRU may decide to abort the direct link establishment. The second rejection message may indicate an identity associated with the target WTRU. The second rejection message may indicate that the maximum number of retries has been reached.

[0066] The relay WTRU may send a rejection message to the source WTRU without attempting to establish a connection with the target WTRU, for example, if the relay WTRU has already received a rejection for a source WTRU different from the target WTRU. The WTRU may receive a first message from the target WTRU. The first message may indicate a rejection associated with a first request to establish a first connection between the first source WTRU and the target WTRU. The first message may indicate a back-off value associated with the target WTRU. The relay WTRU may receive a second message from a second source WTRU. The second message may be associated with a second request to establish a second connection between the second source WTRU and the target WTRU using the relay WTRU. The relay WTRU may send a third message to the second source WTRU indicating that the target WTRU rejected the first request to establish the first connection between the first source WTRU and the target WTRU. The third message may indicate a cause value (e.g., indicating that the target WTRU previously rejected a request to establish a first connection between the first source WTRU and the target WTRU). The relay WTRU may, for example, send the third message without attempting to establish with the target WTRU (e.g., because the relay WTRU has already received rejections for the first source WTRU and the target WTRU). The relay WTRU may determine that a duration associated with the backoff value has expired. The WTRU may send a fourth message to the target WTRU (e.g., based on the determination that a duration associated with the backoff value has expired). The fourth message may be associated with one or more of the first request to establish a first connection between the first source WTRU and the target WTRU or the second request to establish a second connection between the second source WTRU and the target WTRU. The fourth message may be sent based on, for example, a determination that the number of retransmissions associated with establishing a connection with the target WTRU is less than a threshold.The relay WTRU may determine the number of retransmissions. The relay WTRU may receive a fifth message from the target WTRU indicating that the second request to establish a second connection between the second source WTRU and the target WTRU is rejected. The relay WTRU may determine (e.g., based on the fifth message) that the number of retransmissions associated with the connection establishment with the target WTRU is greater than or equal to a threshold. The relay WTRU may send a rejection message to the second source WTRU associated with the pending link establishment connection request (e.g., based on the determination that the number of retransmissions associated with the connection establishment with the target WTRU is greater than or equal to a threshold).

[0067] The WTRU may send a connection establishment request to the target WTRU. The connection establishment request may be a DCR or an LMR. The WTRU may receive a back-off value associated with a connection establishment rejection associated with the target WTRU. The back-off value associated with the connection establishment rejection may be received in response to the transmitted connection establishment request. The WTRU may receive a first message indicating that the WTRU should retry establishing a connection with the target WTRU. The first message may indicate a value associated with a waiting period duration. The WTRU may track a duration associated with the back-off value. Tracking the duration may be started based on receiving a third message from the target WTRU. Tracking the duration may be started based on a determination that the waiting period duration has expired. The WTRU may decide to retry establishing a connection with the target WTRU. The decision to retry establishing a connection with the target WTRU may be based on receiving a third message from the target WTRU indicating to retry establishing the connection. The decision to retry establishing a connection with the target WTRU may be based on a determination that the duration associated with the back-off value has expired. In one example, the WTRU may be a relay WTRU. In the case of a relay WTRU, the connection establishment rejection may be associated with the first source WTRU. The relay WTRU may send a message to the source WTRU indicating that the target WTRU has requested to wait (e.g., based on receiving the rejection message). The relay WTRU may attempt to establish a connection between the source WTRU and the target WTRU.

[0068] A relay (e.g., a U2U relay) may retry if (e.g., when) it receives, for example, a reject message with a back-off time on behalf of the source-end WTRU. The U2U relay may be provisioned with (e.g., receive configuration information indicating) an RSC. The RSC may indicate support for "managed peer connection failure handling." The U2U relay may receive a direct communication request (DCR) or a link modification request (LMR) from the source WTRU to establish a connection via the relay. The request may specify, for example, whether the U2U relay can handle a congestion condition retry procedure on behalf of the source WTRU (e.g., by including "managed failure by source WTRU" or "managed failure by relay"). The U2U relay may send the DCR or LMR to the target WTRU. The U2U relay may receive, for example, a DC reject or link modification reject message from the target WTRU with a code (e.g., #5 or #13) and a back-off time. The U2U relay may send a message to the source WTRU, for example, indicating that it may be waiting for a backoff interval and may be performing some retries on behalf of the source WTRU. For example, the U2U relay may send a DC-Reject / LM-Reject to the source-end WTRU. The DC-Reject / LM-Reject may include a code (e.g., a new code) that may indicate the cause "congestion situation at target WTRU and relay is retrying" and a retry value (e.g., retry count and / or retry time). The DC-Reject / LM-Reject may be a message type "waiting for DCR" or "waiting for link fix." For example, if PC5 link establishment between the U2U relay and the target WTRU may fail, the U2U relay may send a DC-Reject or a Link Fix-Reject to the source WTRU with a code indicating the cause "retry unsuccessful." The source WTRU may decide whether to wait to establish a connection. The source-end WTRU may receive a message indicating "congestion situation at target WTRU and retry."The source-end WTRU may, for example, increase the DCR retransmission time based on receiving the message or stop it (e.g., as the relay handles retries). The source-end WTRU may (e.g., alternatively) cancel (e.g., decide to cancel) the link establishment procedure via the relay, for example, by sending a link release request or PC5-S message (e.g., DCCancel / LMCancel). A relay receiving a message (e.g., a link release request or PC5-S message) may set its retry value (e.g., retry counter) to 0 and ignore (e.g., any) response from the target-end WTRU related to the link establishment / link modification procedure.

[0069] Direct communication (eg, ProSe direct communication) can be established.

[0070] 2 and 3 show example procedures for communication (e.g., 5G ProSe communication) via a WTRU-to-WTRU (U2U) relay (e.g., a 5G WTRU-to-WTRU relay). In an example, a source-end WTRU may discover a target WTRU. The target WTRU may establish a connection with a U2U relay or modify a link (e.g., an existing link) with the U2U relay through a direct communication request (DCR) or a link modification request (LMR). The U2U relay may establish a connection with the target-end WTRU, for example, via a DCR or LMR. The U2U relay may, for example, if (e.g., once) successful (e.g., in the course of communication between the source-end WTRU and the target WTRU), associate with multiple (e.g., two) direct links (e.g., 5G ProSe direct links), for example, one with the source WTRU and another with the target WTRU.

[0071] Figure 2 shows exemplary ProSe communication via a ProSe Layer 3 inter-WTRU relay. Figure 3 shows exemplary ProSe communication via a ProSe Layer 2 inter-WTRU relay.

[0072] The PC5 link between the source ProSe End WTRU and the ProSe End Relay may be shared for multiple target ProSe End WTRUs (e.g., when one source ProSe End WTRU communicates with multiple target ProSe End WTRUs). The PC5 link may be established between the ProSe End Relay and the target ProSe End WTRU (e.g., individually). A Layer 2 link modification procedure may be used, for example, for the shared PC5 link.

[0073] The message (e.g., Direct Link Establishment Execution Reject / Direct Link Modification Execution Reject message) may include an information element (e.g., a PC5 signaling protocol cause information element (IE)) set to a value (e.g., #13 Congestion Status). This may occur if the DCR or LMR fails. The reject message may include a cause value (e.g., #13 Congestion Status), for example, if (e.g., when) the DCR or LMR is rejected (e.g., via a Direct Link Establishment Execution Reject / Direct Link Modification Execution Reject message).

[0074] The target WTRU may provide a back-off value (e.g., a timer value) to the initiating WTRU in a message (e.g., a Direct Link Establishment Execution Rejection message). The target WTRU may refrain from accepting (any) direct link establishment execution requests to relay if (any) back-off value (e.g., via a timer), for example, for NAS-level mobility management congestion control, is active (e.g., running).

[0075] The target WTRU may send a message (e.g., a Direct Link Modification Perform Reject message). The message may be sent via signaling. The message may indicate a cause value (e.g., using PC5 signaling protocol cause value #5 "Lack of resources for 5G ProSe direct link"). The target WTRU may send a message (e.g., a Direct Link Modification Perform Reject message), for example, if the 5G ProSe direct link modification fails (e.g., due to a congestion problem or other temporary lower layer problem causing resource constraints).

[0076] ProSe direct link release may be performed and / or provided.

[0077] An end WTRU at (e.g., either) end of a communication may release the link. The request (e.g., direct link release request performed) may include an IE value indicating a cause, e.g., a #13 congestion situation. The end WTRU may trigger a WTRU-to-network relay reselection, for example, if the end WTRU of a communication releases the link. The end WTRU may trigger a WTRU-to-network relay reselection, for example, if there is a request (e.g., direct link release request performed or direct link release request performed) with a cause IE value.

[0078] The source WTRU may establish a connection to the target WTRU via the U2U relay. The U2U relay may, for example, forward a denial back to the source WTRU if the target WTRU denies the PC5 link establishment or modification. The source WTRU may choose to re-establish the connection or re-select the U2U relay and / or the target WTRU.

[0079] The target WTRU may indicate the reason for the rejection (e.g., in a PC5 Link Establishment / Modification Reject message (#13, #5)). When processing (e.g., processing) a rejection message (e.g., DCR / LMR) at the inter-WTRU relay or source WTRU, the value may be ignored (e.g., not considered). For example, if a rejection cause value (e.g., which may provide a backoff time (e.g., #5, #13)) is received at the inter-WTRU relay or source WTRU, the inter-WTRU relay or source WTRU processing may refrain from explaining (e.g., not explaining).

[0080] The U2U relay may assist in processing the reject message to improve overall performance, for example, if the reject message and its payload (eg, cause IE value) are available to the U2U relay.

[0081] In a scenario where a target WTRU shares a (e.g., single) PC5 link towards a U2U relay, it may be considered to communicate with one or more source WTRUs. For example, a scenario may be considered in which one or more target WTRUs communicate with the same source WTRU via the same U2U relay (e.g., the PC5 link between the U2U relay and the source WTRU is shared).

[0082] The processing of direct communication and link modification reject messages may include one or more of the following scenarios: the U2U relay may attempt to re-establish the connection on behalf of the source WTRU; the U2U relay may inform the source WTRU about the reject message and cause value received from the target WTRU (e.g., while being immediately available to process any other messages); the U2U relay may process (e.g., all) incoming requests from multiple source WTRUs; etc.

[0083] The relay may retry on behalf of the source-end WTRU. The relay may retry, for example, on behalf of the source-end WTRU based on (e.g., upon) receiving a rejection with a backoff time (e.g., a timer).

[0084] 4 shows an example flow for enabling a U2U relay to process a DC / LM rejection message and retry on behalf of the source WTRU. As shown in FIG. 4, the relay may retry on behalf of the source-end WTRU based on (e.g., upon) receiving the rejection with a backoff time (e.g., a timer). One or more of the following may describe actions as shown in FIG. 4, as well as other example and optional procedures.

[0085] A U2U relay may be provisioned with a Relay Service Code (RSC), as shown at 400 in Figure 4. The RSC may indicate its support for "Managed Peer Connectivity Failure Handling."

[0086] As shown in 410 of FIG. 4, service authorization and provisioning may be performed for a source-end WTRU (e.g., a source ProSe-end WTRU), a target-end WTRU (e.g., a ProSe-end WTRU), and / or an inter-WTRU relay (e.g., a ProSe-inter-WTRU relay). The source ProSe-end WTRU may perform discovery of the inter-ProSe WTRU relay. The end WTRUs and relays may be provisioned with an RSC having an indication of support for "managed peer connectivity failure handling." For example, a U2U relay may provide this RSC to manage recovery of a connection failure with the target WTRU on behalf of the source WTRU (e.g., in case of congestion at the target WTRU).

[0087] As shown in 420 of FIG. 4, the source WTRU may determine whether to use an existing PC5 link toward the U2U relay WTRU. For example, if the existing PC5 link may be selected, an LMR may be sent to the U2U relay. A DCR may be sent to the U2U relay (e.g., if not). The source WTRU may specify whether the U2U relay can retry on behalf of the source WTRU, for example, by including "Failure Managed by Source WTRU" or "Failure Managed by Relay" and / or one or more of the following: the (e.g., maximum) number of retries the U2U relay can perform, the (e.g., maximum) amount of time it may wait, etc. These values ​​may be negotiated between the source WTRU and the relay, for example, during PC5 link establishment / modification.

[0088] As shown in 430 of Figure 4, the U2U relay may determine whether to use the existing PC5 link toward the target WTRU. The LMR may, for example, send an LMR to the target WTRU if the existing PC5 link is selected. A DCR may be sent to the target WTRU (e.g., if not).

[0089] As shown in 440 of FIG. 4, the target WTRU may respond to the U2U relay with a DC Reject or Link Modification Reject message with a cause code (e.g., #5 or #13). The target WTRU may respond with a backoff time (e.g., a timer). The target WTRU may respond with a DC Reject or LMR message with a cause code along with the backoff time to the U2U relay.

[0090] As shown in 450 of Figure 4, the U2U relay may locally start tracking the back-off time (e.g., via a back-off timer), for example, if the source WTRU indicated in the initial DCR / LMR that the U2U relay can retry establishing a connection to the target WTRU (e.g., at 420 of Figure 4), or if the RSC is provisioned to support "managed peer connection failure handling." Different U2U relays may choose to do different things, for example, based on agreed-upon failure management.

[0091] As shown in 460 of Figure 4, the U2U relay may send a message to the source-end WTRU indicating, for example, one or more of the following: a cause code received from the target WTRU indicating that the rejection may be from the target WTRU, indicating that the relay may be waiting and performing some retries (e.g., a specified number of retries) on behalf of the source WTRU, etc. The message may include (any of) a DC-Accept, LM-Accept, DC-Reject, or LM-Reject message type with a (e.g., new) code that may indicate the cause "congestion situation at the target WTRU and the relay is retrying." The message may be a different (e.g., new) message type, such as, for example, "DC Wait," "Wait for Link Fix," or DC Ack.

[0092] A source-end WTRU receiving a message with "Congestion situation and relay retrying" may increase the retry time (e.g., timer) for the DCR / LMR or may stop tracking the time (e.g., so the relay can handle the retries).

[0093] The source-end WTRU may (e.g., alternatively) decide to cancel the link establishment / modification (e.g., via a relay). For example, the source-end WTRU may cancel the link by sending a link release request (e.g., ProSe Link Release Request) or a (e.g., new) PC5-S message (e.g., DCCancel / LMCancel). In this case, the relay receiving this message may set the number of retries to zero (0) (e.g., via a retry counter) and may ignore (e.g., any) response from the target-end WTRU related to this link establishment or modification procedure.

[0094] This message (eg, as shown in FIG. 4 at 460) may be used, for example, to periodically notify the source WTRU that the U2U relay is still retrying.

[0095] As shown in 470 of FIG. 4, the U2U relay WTRU may retransmit the DCR / LMR message to the target WTRU at the end of the duration (e.g., timer expiration), e.g., if the number of retransmissions is less than the number of retries performed so far and the elapsed time is less than the maximum time the source WTRU will wait (e.g., as specified by the source WTRU). As shown in FIG. 4, the actions at 440, 450, 460, and 470 may be repeated (e.g., several times). The action associated with 460 of FIG. 4 may be performed (e.g., only once) if (e.g., when) the first rejection message is received at the relay. It may be understood by the source WTRU and the relay (e.g., based on the actions associated in 410 and 420) that the relay may be processing the retransmission and that the process at 460 may be optional.

[0096] As shown in FIG. 4 at 480, the target WTRU may respond, for example, with a reject message (eg, DC-reject / LM-reject).

[0097] 4, a relay may send a DC-Reject or Link Modification-Reject with a (e.g., new) code (which may, for example, point to cause "retry unsuccessful") if, for example, the (e.g., maximum) number of retries has been reached. This message may indicate that "maximum retry attempts have been made."

[0098] The relay may send an accept message, such as a DC-Accept or an LM-Accept (eg, cause IE set to "retry successful"), if, for example, link establishment is successful.

[0099] In an example, (for example) the U2U relay may use a DCA message to notify the source WTRU of a pending connection establishment / modification with the target WTRU (e.g., with respect to 460 in FIG. 4). The U2U relay may send an LMR message to the source WTRU, which may include an indication of successful completion of the connection with the target WTRU. The U2U relay may receive an LMA message from the source WTRU confirming the source WTRU's acceptance of the connection / communication with the target WTRU. The U2U relay may send (for example) a Link Release Request message indicating unsuccessful completion of the connection with the target WTRU.

[0100] The source-end WTRU may associate the rejection message with the target-end WTRU, and relays may be available to reach other target WTRUs.

[0101] FIG. 5 shows an example flow for enabling a source WTRU to be notified of a target WTRU's request rejection and its cause. This message informing the source WTRU may enable the source WTRU to understand that the rejection originates from the target WTRU. The rejection does not have to originate from a U2U relay. The same U2U relay can be (re)used to reach the same or a different target WTRU. As shown in FIG. 5, the source-end WTRU may associate the rejection message with the target-end WTRU. Relays may be available to reach other target WTRUs.

[0102] The source WTRU may send a request to establish a connection with target WTRU#1 via the U2U relay, as shown at 510 in Figure 5. Target WTRU#1 may then reject the request.

[0103] As shown in 520 of FIG. 5, the U2U relay WTRU may respond to the source WTRU with a DC / LM rejection message with a cause value. The (e.g., new) cause value may indicate that it may be the target end WTRU #1 that rejected the request. The specified message and cause value may point to the target WTRU (e.g., may not point to the U2U relay). It may indicate to the source WTRU that the retry cannot be processed by the U2U relay. This message may include the cause value that target WTRU #1 sent to the U2U relay with its rejection message (e.g., security issue). The U2U relay may manage a time window to wait for multiple response messages, for example, in a scenario where the U2U relay sends messages to multiple target WTRUs. The U2U relay may send a consolidated rejection to the source WTRU, for example, at (e.g., after waiting until) the end of the time window.

[0104] 5, the source WTRU may start tracking the retry time (e.g., via a retry timer), e.g., based on the received backoff value. The source WTRU may associate the retry time (e.g., a timer) with target end WTRU#1.

[0105] 5, the source-end WTRU may (re)select the (e.g., same) U2U relay to reach the same (e.g., after a backoff timer) or another target-end WTRU (e.g., target WTRU #2). This may be possible, for example, because the (e.g., now) source WTRU may recognize that the previous rejection came from the target WTRU (e.g., not the U2U relay), and therefore the U2U relay may be available to handle other requests.

[0106] The relay may send a rejection directly to the second source-end WTRU, for example, if (eg, when) the backoff time is being tracked (eg, its backoff timer is running).

[0107] 6 illustrates an example flow that may allow (e.g., enable) a U2U relay to process multiple requests to the same target WTRU (e.g., from two or more source WTRUs) when the target WTRU has previously rejected (e.g., was rejecting) the request. Scenarios may include when the target WTRU shares a link (e.g., a single PC5 link) with a U2U relay, for example, when it is communicating (e.g., communicating) with multiple source WTRUs.

[0108] As shown in FIG. 6, the relay may send a rejection (e.g., directly) to the second source-end WTRU if (e.g., when) a backoff time is active or being tracked (e.g., its backoff timer is running).

[0109] As shown in 610 of FIG. 6, authorization and discovery may be performed (e.g., as described herein). As shown in 620 of FIG. 6, the source WTRU#1 may send a DCR / LMR to the U2U relay (e.g., as described herein). As shown in 630 of FIG. 6, the U2U relay may send a DCR / LMR to the target WTRU (e.g., as described herein). As shown in 640 of FIG. 6, the target WTRU may respond with a rejection message (e.g., as described herein). As shown in 650 of FIG. 6, the U2U relay may start tracking a back-off time (e.g., via a back-off timer), for example, as described herein.

[0110] As shown in 660 of FIG. 6, the U2U relay WTRU may send a message to the source WTRU#1. The message may notify that the target WTRU has rejected the DCR / LMR with a cause value and a backoff time (e.g., a timer). The relay or the source WTRU may handle a retry procedure with the target WTRU. The relay may keep track of the rejection and backoff time from the target WTRU. The relay may keep track of the state of the target WTRU, for example, "rejected" or "congested."

[0111] As shown at 670 in FIG. 6, the U2U relay may receive a DCR / LMR from source WTRU#2 for communication with the same target end WTRU (e.g., which returned a rejection message with a backoff time to the relay at 640 in FIG. 6).

[0112] As shown in 680 of FIG. 6, the U2U relay WTRU may, for example, send (e.g., immediately send) a response message to the source WTRU#2 with a (e.g., new) cause value / message type (e.g., as described herein) to the source WTRU#2 (e.g., if the backoff time has not expired). This message may indicate that the target end WTRU previously rejected the request (e.g., via a (e.g., new) cause code). In an example, this indication may include the cause of the rejection (e.g., congestion) indicated by the target WTRU. This message may be an immediate response and may indicate that the U2U relay is not attempting to establish the connection and may retry when the current backoff time expires. It may specify the remaining time of the current backoff time. In an example, this message may be optional.

[0113] The relay may (e.g., alternatively) use the backoff time associated with the target WTRU for each requesting source WTRU, in which case the relay may, for example, respond to source WTRU#2 without sending a request to the target WTRU and start tracking the source WTRU#2 backoff time (e.g., via a timer).

[0114] As shown at 490 in FIG. 7, the U2U relay may track (e.g., all) pending requests (e.g., associate them with an ongoing backoff time) and, for example, when the U2U relay processes a retry with a target WTRU, may apply the ongoing backoff time to (e.g., all) received requests to the same target WTRU (e.g., requests from source WTRU #2).

[0115] As shown in 492 of FIG. 7, the back-off time may expire at the U2U relay. For example, if the U2U relay is processing a retry with the target WTRU, the U2U relay may transmit (e.g., all) pending DCR / LMR requests from (e.g., each) corresponding source WTRU to the target end WTRU. The relay may (e.g., alternatively) process a back-off time for each source WTRU and transmit (e.g., only) the pending request from the source WTRU associated with the expired back-off time to the target WTRU. If the U2U relay is not processing a retry, the U2U relay may (e.g., alternatively) reset the state associated with the target WTRU to “normal” (e.g., upon back-off time expiration).

[0116] 7, the target WTRU may send a reject message (e.g., a DC / LM Reject with a Cause IE) to the U2U relay, for example, after the U2U relay has sent a DCR / LMR (e.g., multiple DCR / LMRs associated with multiple pending source-end WTRUs). The U2U relay may determine that the maximum number of retries has been attempted.

[0117] As shown in 496 of FIG. 7, for example, if the U2U relay handles retries with the target WTRU, and if the U2U relay receives a rejection message from the target-end WTRU and the maximum retries have been reached, the relay may send a rejection message back to the source-end WTRU (e.g., both source-end WTRUs as shown in FIG. 6). This message may indicate "retry unsuccessful." This message may also indicate "maximum retry attempts made." If the retries are successful, this message may indicate "retry successful."

[0118] The target wireless transceiver unit (eg, WTRU) may enable a wait-retry response (eg, transmit / receive).

[0119] The wait-retry response may be applicable to inter-WTRU communication scenarios.

[0120] A U2U relay may be used (e.g., as described herein), which may be applicable to direct WTRU-to-WTRU communication scenarios where a relay is not used. In such scenarios, the U2U relay procedures described above may be applied to the target WTRU.

[0121] For example, the target WTRU may refrain from (e.g., be unable to) accept the DCR / LMR (e.g., currently). The target WTRU may delay / accept the request at a later time (e.g., the target WTRU may anticipate that the cause of the rejection will be resolved in the next few seconds). There may be no way for the target WTRU to convey this to the relay or source WTRU, for example, other than rejecting the request entirely (e.g., all together).

[0122] The target WTRU may refrain from rejecting the request (e.g., not reject it directly). For example, the target WTRU may ask the requesting WTRU (e.g., a relay or another WTRU) to wait. The message may include a (e.g., new) code that may point to the cause "wait - try again later" (e.g., as specified for U2U relays as described herein) and may indicate how long to wait.

[0123] The source WTRU may delay starting the back-off time (e.g., based on (e.g., upon) receipt), e.g., until it receives a follow-up / update message from the target WTRU or until a waiting period specified by the target WTRU has elapsed. Otherwise, the source WTRU may stop waiting and (e.g., once) the time has expired, e.g., if the source WTRU receives a message with a cause IE "retry" (e.g., DC / LM reject), start the back-off time, and retry with a different (e.g., new) configuration (e.g., if any).

[0124] The relay may receive a response to the DCR / LMR. The relay may delay the start of a backoff time (e.g., until it receives a follow-up / update message from the target WTRU or until a waiting period specified by the target WTRU has elapsed), and the U2U relay may delay sending a DC / LM Reject message to the source WTRU, for example, if (e.g., when) the relay receives a response to the DCR / LMR from the target WTRU with "requesting WTRU will wait and retry later." The U2U relay may (e.g., immediately respond to) a received (e.g., new) DCR / LMR message from another WTRU indicating "target WTRU requested to wait," for example, if (when) multiple source WTRUs attempt to send DCR / LMRs to the same target WTRU. The U2U relay may, for example, receive a message (e.g., DC / LM Reject) with a cause IE "retry" if the target WTRU may (e.g., can accept) the request but prefers that the connection be re-established. In this scenario, the U2U relay may initiate a backoff time and, for example, if the time expires (e.g., once), retry with a different (e.g., new) configuration (e.g., if any).

[0125] A relay (e.g., a U2U relay) may retry if (e.g., when) it receives, for example, a reject message with a backoff time on behalf of the source-end WTRU. The U2U relay may be provisioned with (e.g., receive configuration information indicating) an RSC. The RSC may indicate support for "managed peer connection failure handling." The U2U relay may receive a DCR or LMR from the source WTRU to establish a connection via the relay. The request may specify, for example, whether the U2U can handle a congestion condition retry procedure on behalf of the source WTRU (e.g., by including "managed failure by source WTRU" or "managed failure by relay"). The U2U relay may send a DCR or LMR to the target WTRU. The U2U relay may receive, for example, a DC reject or link modification reject message from the target WTRU, with a code (e.g., #5 or #13) and a backoff time. The U2U relay may send a message to the source WTRU, for example, indicating that it is waiting a backoff interval and performing several retries on behalf of the source WTRU. For example, the U2U relay may send a DC-Reject / LM-Reject to the source-end WTRU. The DC-Reject / LM-Reject may include a code (e.g., a new code) that may indicate the cause "congestion situation at target WTRU and relay is retrying" and a retry value (e.g., retry count and / or retry time). The DC-Reject / LM-Reject may be a message type "waiting for DCR" or "waiting for link fix." For example, if PC5 link establishment between the U2U relay and the target WTRU fails, the U2U relay may send a DC-Reject or a link fix-Reject to the source WTRU with a code indicating the cause "retry unsuccessful." The source WTRU may decide whether to wait to establish a connection. The source-end WTRU may receive a message indicating "congestion situation at target WTRU and retry."The source-end WTRU can increase the retransmission time of the DCR or stop it (e.g., based on receiving the message, e.g., as the relay processes the retries). The source-end WTRU can (e.g., alternatively) cancel (e.g., decide to cancel) the link establishment procedure via the relay, e.g., by sending a link release request or PC5-S message (e.g., DCCancel / LMCancel). A relay receiving a message (e.g., a link release request or PC5-S message) can set its retry value (e.g., retry counter) to 0 and ignore (e.g., any) response from the target-end WTRU related to the link establishment / link modification procedure. In an example, the source-end WTRU can associate a rejection message with the target-end WTRU (e.g., a relay may be available to reach other target WTRUs). The source WTRU can send a DCR / LMR to establish a connection with the target WTRU (e.g., via the relay). The source WTRU may receive a message from the U2U relay that may include a cause value indicating that the relay is performing some retries on behalf of the source WTRU (e.g., the cause value may not be applicable to the relay, but may be applicable to the target-end WTRU, e.g., DCR-wait-retry, LMR-wait-retry, DC-reject, LM-reject, etc.). The source WTRU may associate the reject condition with the target-end WTRU and refrain from associating the reject condition with the U2U relay itself. The source WTRU may, for example, send a DCR / LMK to establish a connection with another target WTRU via the relay from which the DC-reject / LM-reject was received (e.g., the same relay).

[0126] In an example, the relay may send a rejection to the second source-end WTRU (e.g., directly) if (e.g., when) the back-off time is being tracked (e.g., the back-off timer is running). The U2U relay may receive a DCR / LMR from the second source WTRU, for example, to communicate with the (e.g., the same) target-end WTRU (which may have returned a rejection with the back-off time to the relay). The U2U relay may handle a retry procedure with the second source WTRU. The U2U relay WTRU may track the back-off time. The back-off time may be associated with the target WTRU. While tracking the back-off time, the U2U relay WTRU may send (e.g., immediately) a rejection message (e.g., DCR-wait-retry, LMR-wait-retry, DC-reject, LM-reject, etc.) to the second source WTRU, for example, with a cause value indicating "target-end WTRU previously rejected the request" without attempting to reach the target WTRU. The U2U relay may track pending requests from the source WTRU (e.g., associate it with an ongoing / tracked backoff time). The U2U relay may apply the tracked backoff time to requests to the (e.g., same) target-end WTRU. The U2U relay may send pending (e.g., all pending) DCR / LMR requests from (e.g., each) corresponding source WTRU to the target-end WTRU (e.g., when the backoff time expires and / or the retry count exceeds 0). For example, if the U2U relay receives a reject message from the target-end WTRU and the maximum retries have been reached, the relay may send a reject message back to (e.g., all) source-end WTRUs waiting for link establishment / modification responses.

[0127] In an example, the wait-retry response may be sent / received at the target (e.g., with or without a relay). For example, the target WTRU may receive a DCR / LMR to establish a connection (e.g., via a relay or directly from the source WTRU). The target WTRU may send a DC / LM reject message with a cause indicating "requesting WTRU will wait and retry later." The message may (e.g., alternatively) be a different (e.g., new) message type, such as "waiting for DCR" or "waiting for link fix." The message may indicate how long the source WTRU and / or U2U relay can wait for a response from the target WTRU and / or before retrying or triggering a WTRU reselection procedure. The U2U relay may receive a message with a cause indicating "requesting WTRU will wait and retry later." The U2U relay may delay starting tracking the back-off time, for example, until it receives a follow-up / update message from the target WTRU or until a waiting period specified by the target WTRU has elapsed. The U2U relay may delay sending a DC / LM reject message to the source WTRU. The U2U relay may respond (e.g., immediately) to a DCR / LMR message received from another WTRU indicating "target WTRU requested to wait." The U2U relay may receive a message (e.g., DC / LM reject) with a cause IE "retry," for example, if the target WTRU can accept the request but prefers that the connection be re-established (e.g., conditions associated with re-establishing the connection are determined). In this case, the U2U relay may start tracking a back-off time and, for example, retry with a different configuration (e.g., if any) when the time expires. The U2U may send a pending DCR / LMR message from another source WTRU to the target WTRU, for example, if (e.g., when) the time expires. The source WTRU may receive a message from the target WTRU indicating a cause indicating "requesting WTRU will wait and retry later."The source WTRU may delay starting tracking the back-off time, for example, until it receives a follow-up / update message from the target WTRU or until a waiting period specified by the target WTRU has elapsed. Otherwise, the source WTRU may start tracking the back-off time and retry with a different configuration (e.g., if any) if the time expires, for example, if the source WTRU receives a message with a cause IE "retry" (e.g., DC / LM reject).

[0128] Although the above-described features and elements are described in particular combinations, each feature or element may be used alone without the other features and elements of the preferred embodiments, or may be used in various combinations with or without the other features and elements.

[0129] While the implementations described herein may consider 3GPP-specific protocols, it will be understood that the implementations described herein are not limited to this scenario and may be applicable to other wireless systems. For example, while the solutions described herein consider LTE, LTE-A, new radio (NR), or 5G-specific protocols, it will be understood that the solutions described herein are not limited to this scenario and may be applicable to other wireless systems.

[0130] The processes described above may be implemented in a computer program, software, and / or firmware embodied in a computer-readable medium for execution by a computer and / or processor. Examples of computer-readable media include, but are not limited to, electronic signals (transmitted via wired and / or wireless connections) and / or computer-readable storage media. Examples of computer-readable storage media include, but are not limited to, read-only memory (ROM), random-access memory (RAM), registers, cache memory, semiconductor memory devices, magnetic media such as, but not limited to, internal hard disks and removable disks, magneto-optical media, and / or optical media such as compact discs (CD-ROM) disks and / or digital versatile discs (DVDs). A processor in association with software may be used to implement a radio frequency transceiver for use in a WTRU, a terminal, a base station, a radio network controller (RNC), and / or any host computer.

Claims

1. A relay wireless transmit / receive unit (WTRU), comprising: sending a transmission to the target WTRU associated with the source WTRU; receiving a rejection message associated with the transmission from the target WTRU, the rejection message indicating a back-off time value; determining a number of retransmissions associated with said transmission; determining message content based on a number of retransmissions associated with the transmission; transmitting the message content to the source WTRU; a relay WTRU configured to perform

2. based on a determination that a number of retransmissions associated with the transmission is below a threshold, the message content including an indication of the back-off time value; based on a determination that a number of retransmissions associated with the transmission is greater than or equal to the threshold, the message content indicating a rejection associated with the transmission. The relay WTRU of claim 1 .

3. The relay WTRU of claim 1 , wherein the message content indicates that the relay WTRU attempts a retransmission on behalf of the source WTRU based on a determination that a number of retransmissions associated with the transmission is below a threshold.

4. The relay WTRU of claim 1 , wherein the message content indicates a number of retransmission attempts based on a determination that a number of retransmissions associated with the transmission is below a threshold.

5. The relay WTRU of claim 1 , wherein the message content indicates identification information associated with the target WTRU based on a determination that a number of retransmissions associated with the transmission is greater than or equal to a threshold.

6. The relay WTRU of claim 1 , wherein the message content indicates that a maximum number of retransmissions has been reached based on a determination that a number of retransmissions associated with the transmission is greater than or equal to a threshold value.

7. The relay WTRU of claim 1 , wherein the transmission is a direct communication request (DCR) or a link modification request (LMR).

8. 1. A method performed by a relay wireless transmit / receive unit (WTRU), comprising: sending a transmission to the target WTRU associated with the source WTRU; receiving a rejection message associated with the transmission from the target WTRU, the rejection message indicating a back-off time value; determining a number of retransmissions associated with said transmission; determining message content based on a number of retransmissions associated with the transmission; transmitting the message content to the source WTRU; A method comprising:

9. based on a determination that a number of retransmissions associated with the transmission is below a threshold, the message content including an indication of the back-off time value; based on a determination that a number of retransmissions associated with the transmission is greater than or equal to the threshold, the message content indicating a rejection associated with the transmission.

9. The method of claim 8.

10. The method of claim 8 , wherein the message content indicates that the relay WTRU attempts a retransmission on behalf of the source WTRU based on a determination that a number of retransmissions associated with the transmission is below a threshold.

11. The method of claim 8 , wherein the message content indicates a number of retransmission attempts based on a determination that the number of retransmissions associated with the transmission is below a threshold.

12. The method of claim 8 , wherein the message content indicates identification information associated with the target WTRU based on a determination that a number of retransmissions associated with the transmission is greater than or equal to a threshold.

13. The method of claim 8 , wherein the message content indicates that a maximum number of retransmissions has been reached based on a determination that a number of retransmissions associated with the transmission is greater than or equal to a threshold value.

14. The method of claim 8 , wherein the transmission is a direct communication request (DCR) or a link modification request (LMR).

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