Patent Description:
The standard from Etsi: "3GPP TS <NUM> V16. <NUM> Release <NUM>" discloses a PC5 unicast link identifier update procedure between an initiating UE and a target UE.

In examples, the end-to-end (E2E) link identifications (IDs) may be isolated per-hop, so that changes of link IDs may not impact other E2E/per-hop links (e.g., a Linked Identifier Update (LIU) procedure may run between a WTRU and the relay). A relay (e.g., a relay WTRU) may allocate R-specific security IDs/session key identifiers (e.g., most significant bits (MSBs)/ least significant bits (LSBs) of Knrp-sess ID). The relay (e.g., relay WTRU) may replace the security IDs/session key identifiers received from peer WTRUs with R-specific security IDs/session key identifiers, for example, if forwarding a message. In examples, per-hop IDs and E2E IDs may be added to link identifier update messages. In examples, the support application layer ID and IP address/prefix may be changed using a link modification procedure (e.g., between E2E peer WTRUs), which may be executed during the LIU procedure run between a WTRU and a WTRU-to-WTRU relay.

In examples, a WTRU may send a Direct Communication Request (DCR) message. The DCR message may not include an adaptation header. The DCR message may be sent for a discovery and link establishment request (e.g., integrated discovery). A relay (e.g., relay WTRU) may receive the DCR message. The relay (e.g., relay WTRU) may add an adaptation header to the DCR message before forwarding it.

In examples, for standalone discovery, announcement and solicitation messages may be sent without an adaptation header. A relay (e.g., relay WTRU) may add an adaptation header before forwarding the messages. The response message may be sent with the adaptation header from the responding WTRU. In examples, no adaptation header may be used, and the E2E ID may be added to the message payload.

In examples, a relay (e.g., a relay WTRU) for establishing an E2E link may be provided. The relay WTRU may include a processor. The processor may be configured to receive a first message from a first WTRU. The first message may indicate MSBs for the first WTRU that may be associated with a session key identifier. The processor may be configured to send a second message to a second WTRU. The second message may indicate relay MSBs. The relay MSBs may be associated with the MSBs for the first WTRU and may be associated with the session key identifier. The processor may be configured to send a third message to the first WTRU. The third message may indicate relay LSBs. The relay LSBs may be associated with LSBs for the second WTRU and may be associated with the session key identifier.

By way of example, the WTRUs 102a, 102b, 102c, 102d, any of which may be referred to as a "station" and/or a "STA", may be configured to transmit and/or receive wireless signals and may include a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a subscription-based unit, a pager, a cellular telephone, a personal digital assistant (PDA), a smartphone, a laptop, a netbook, a personal computer, a wireless sensor, a hotspot or Mi-Fi device, an Internet of Things (loT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and/or other wireless devices operating in an industrial and/or an automated processing chain contexts), a consumer electronics device, a device operating on commercial and/or industrial wireless networks, and the like.

Thus, in one embodiment, the base station 114a may include three transceivers, e.g., one for each sector of the cell.

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

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

The CN <NUM>/<NUM> may provide call control, billing services, mobile location-based services, pre-paid calling, internet connectivity, video distribution, etc., and/or perform high-level security functions, such as user authentication.

As shown in <FIG>, the WTRU <NUM> may include a processor <NUM>, a transceiver <NUM>, a transmit/receive element <NUM>, a speaker/microphone <NUM>, a keypad <NUM>, a displayltouchpad <NUM>, non-removable memory <NUM>, removable memory <NUM>, a power source <NUM>, a global positioning system (GPS) chipset <NUM>, and/or other peripherals <NUM>, among others.

The processor <NUM> of the WTRU <NUM> may be coupled to, and may receive user input data from, the speaker/microphone <NUM>, the keypad <NUM>, and/or the displayltouchpad <NUM> (e.g., a liquid crystal display (LCD) display unit or organic light-emitting diode (OLED) display unit). The processor <NUM> may also output user data to the speaker/microphone <NUM>, the keypad <NUM>, and/or the displayltouchpad <NUM>.

The peripherals <NUM> may include one or more sensors, the sensors may be one or more of a gyroscope, an accelerometer, a hall effect sensor, a magnetometer, an orientation sensor, a proximity sensor, a temperature sensor, a time sensor; a geolocation sensor, an altimeter, a light sensor, a touch sensor, a magnetometer, a barometer, a gesture sensor, a biometric sensor, and/or a humidity sensor.

A WLAN in infrastructure Basic Service Set (BSS) mode may have an Access Point (AP) for the BSS and one or more stations (STAs) associated with the AP. 11e DLS or an <NUM>.

Sub <NUM> modes of operation are supported by <NUM> at and <NUM> ah. The channel operating bandwidths, and carriers, are reduced in <NUM> af and <NUM> ah relative to those used in <NUM>. 11n, and <NUM> ac.

In examples, a relay (e.g., a relay WTRU) for establishing an end-to-end (E2E) link may be provided. The relay WTRU may include a processor. The processor may be configured to receive a first message from a first WTRU. The first message may indicate most significant bits (MSBs) for the first WTRU that may be associated with a session key identifier. The processor may be configured to send a second message to a second WTRU. The second message may indicate relay MSBs. The relay MSBs may be associated with the MSBs for the first WTRU and may be associated with the session key identifier. The processor may be configured to send a third message to the first WTRU. The third message may indicate relay least significant bits (LSBs). The relay LSBs may be associated with LSBs for the second WTRU and may be associated with the session key identifier.

In V2X examples, there may be a privacy requirement that may state that the application layer ID and Layer <NUM> (L2) ID need to be changed over time. This may ensure that the WTRU may not be tracked or identified by other WTRUs. The eV2X WTRU IP address/prefix may be (e.g., may also be) changed if IP communication is used. In examples, a Link Identifier Update (LIU) procedure may be used to change the IDs on a WTRU.

In LIU procedure examples, peer WTRUs may change their IDs during the same procedure run (e.g., both WTRUs may change their identifiers at the same time to avoid linkability issues). There may be a linkability issue if a WTRU (e.g., only one WTRU) changes its ID. In examples, a malicious WTRU may track eV2X WTRUs by determining that WTRU1 IDs may have changed to values (e.g., new values) by linking them with WTRU1 peer WTRU IDs.

In examples, the security IDs/session key identifiers (e.g., MSBs/LSBs of Knrp-sess ID) may (e.g., may also) change when changing the other IDs.

Security IDs/session key identifiers may be the Knrp-sess ID. The MSBs of Knrp-sess ID may be defined by the source WTRU (e.g., sending a DCR message). The LSBs of Knrp-sess ID may be defined by the responding WTRU (e.g., sending a DSM Command message).

During the PC5 unicast link establishment, a WTRU (e.g., each WTRU) may validate that the MSBs/LSBs of Knrp-sess ID may be locally unique. The MSBs/LSBs of Knrp-sess ID may be sent in cleartext with a packet (e.g., each packet) and may be used at the PDCP layer to retrieve the security context associated with a PC5 unicast link. The security context may include the keys derived for (de)encryption, integrity protection/validation, etc..

The LIU procedure may be used to change both peer WTRUs IDs, for example, L2 IDs and the MSBs/LSBs of Knrp-sess ID (e.g., security IDs/session key identifiers).

<FIG> illustrates an example of an L2 WTRU-to-WTRU relay. A secured (e.g., "extended") PC5 link may be set up between the source WTRU and the target WTRU via the WTRU-to-WTRU relay. The source/target WTRUs may send messages to the WTRU-to-WTRU relay and may receive messages from the WTRU-to-WTRU relay. In examples, the security association and the PC5 unicast link may be established (e.g., established directly) between the source WTRU and target WTRU. The source/target WTRUs may detect that the communication may be going through a WTRU-to-WTRU relay if the source/target WTRUs detect a relay indication and/or relay identifier (RID) included in the received messages.

The source/target WTRUs may use a link (e.g., a unique link and/or a per-hop link) to send messages toward a specific relay. For example, if a source WTRU communicates with two target/peer WTRUs (e.g., WTRU2 and WTRU3) via the same relay, then the source WTRU may use the same per-hop link to send messages toward its peer WTRUs. The per-hop link may be identified by a pair of L2 IDs. The specific end-to-end unicast links (e.g., between source WTRU-WTRU2 and source WTRU-WTRU3) may be differentiated by using an adaptation layer header. The adaptation layer header may include information identifying the specific source/target WTRUs.

The WTRU-to-WTRU relay may maintain a mapping table including the mapping of peer WTRUs end-to-end IDs and the corresponding relay-L2 IDs that have been self-assigned. If the WTRU-to-WTRU relay receives a message, the WTRU-to-WTRU relay may use its mappings table to find the end-to-end source and destination IDs to be used to forward the received message to the target WTRU. The WTRU-to WTRU relay may update the source and destination L2 ID fields of the received message to the target per-hop link and the end-to-end IDs specified in the adaptation header with its corresponding WTRU's ID and relay ID before forwarding the message.

The relay may receive messages from a source/target WTRU to be relayed to a target/source WTRU. The relay may first update the source/destination L2 IDs to the per-hop IDs that may indicate where to send the messages. The relay may allocate specific IDs for the source/target WTRUs used to replace the IDs specified in the adaptation header. The source/target WTRUs may not know their peer WTRU end-to-end IDs.

In examples, a management unicast link may be established between the WTRU (e.g., source and/or target WTRU) and the relay WTRU. This unicast link may be used to manage associated extended links going through the relay WTRU. The extended links may be associated with the same RID as the management link. The management link may be secured (e.g., integrity and confidentiality protected) between the source and/or target WTRU and the relay WTRU, for example, between the WTRU1 and the WTRU-to-WTRU relay in <FIG> (the management link is not shown). For example, the source WTRU and its peer WTRU may need to change their identifiers. The management link may be used between the source/target WTRUs and the relay to inform the relay about the IDs (e.g., new IDs) to be used at the source/target WTRUs.

A WTRU (e.g., WTRU1) may have a per-hop link to a relay. The WTRU (e.g., WTRU1) may have an E2E PC5 unicast link with a peer WTRU (e.g., WTRU2). A privacy trigger may occur on WTRU1 (e.g., a privacy timer expires). IDs (e.g., all IDs) may need to be changed (e.g., at the same time) and on both peer WTRUs. Changing IDs on both sides may be needed to avoid linkability of unchanged IDs to (e.g., new) IDs. IDs (e.g., new IDs and unchanged IDs) may be sent in cleartext with messages (e.g., all messages) and may be visible to everyone.

Considering the relayed E2E connections, E2E IDs (e.g., new E2E IDs) may be introduced in the adaptation header. The E2E IDs (e.g., new E2E IDs) may need to be changed during the same procedure since these identifiers may be sent in cleartext. IDs (e.g., all IDs) may be changed at the same time, for example, per-hop L2 IDs, E2E IDs, and/or E2E security IDs/session key identifiers. WTRU1, relay WTRU, and/or WTRU2 may be involved in the identifiers update procedure.

The current LIU procedure/messages may handle the change of L2 IDs and security IDs/session key identifiers for a direct unicast link. The current LIU procedure/messages may not handle the change of E2E IDs that are transported in cleartext and may be (e.g., may need to be) privacy protected.

WTRU1 may have established E2E links via the relay with multiple peer WTRUs (e.g., WTRU2, WTRU3,. A privacy update procedure may be triggered on WTRU1. The change of IDs (e.g., per hop L2 IDs, E2E IDs, and/or E2E security IDs/session key identifiers) at WTRU1 may affect its E2E peer WTRUs and the relay (e.g., for forwarding table), potentially causing a signaling storm due to an exchange (e.g., a massive exchange) of PC5-S messages at the same time.

Source WTRU (S-WTRU) and target WTRU (T-WTRU) may be used to identify peer WTRUs. S-WTRU and T-WTRU terminology may be provided as follows: S-WTRU may be called: initiating WTRU, source WTRU, peer WTRU, and/or WTRU1. T-WTRU may be called: responding WTRU, target WTRU, peer WTRU, destination WTRU, and/or WTRU2.

A WTRU-to-WTRU relay may be a WTRU behaving as a relay between two peer WTRUs. Terminology for a WTRU-to-WTRU relay may be provided as follows: R-WTRU, relay WTRU, and/or relay. A PC5 unicast link established between two WTRUs via a WTRU-to-WTRU relay may be called an E2E link. Terminology for E2E link may be provided as follows: E2e link, e2e link, or E2E link. E2E link IDs terminology may include, e.g.: E2E IDs (e.g. E2E L2 IDs uniquely identifying an E2E link) and E2E security info/IDs/session key identifiers (e.g., MSBs and LSBs of Knrp-sess ID).

If a WTRU changes its IDs, the relay and its peer WTRUs may need to change their IDs (e.g., at the same time). This may create a signaling storm of PC5-S message exchanges. The E2E links may be isolated on a per-hop basis (e.g., to avoid this situation). For example, E2E link IDs, which are sent in cleartext (e.g., in the header of the message), may be specific to the per-hop link. This may be handled at the relay by replacing the received E2E link IDs with corresponding relay-specific IDs (e.g., S-WTRU's E2E ID (e.g., ID1)) and E2E MSBs of Knrp-sess ID (e.g., MSBs1) may be replaced by relay-specific E2E IDs (e.g. R-ID1) and relay-specific MSBs of Knrp-sess ID (e.g., R-MSBs1)). E2E peer WTRUs may not know their peer WTRU's IDs. If IDs need to be changed on a WTRU, the IDs used between this WTRU (e.g., the WTRU onto which the IDs need to be changed) and the relay may be updated. The relay may update its mapping table. For example, the relay may generate IDs (e.g., new IDs) and associate them with their corresponding IDs used with E2E peer WTRUs. The peer WTRUs may not be (e.g., may not need to be) involved in the LIU procedure if triggered on the source WTRU. WTRUs (e.g., all WTRUs) may trigger the LIU procedure if needed (e.g., when a trigger is received), which may involve the relay. E2E peer WTRUs' IDs may be decoupled at the relay, which may ensure that E2E peer WTRUs' IDs are not transmitted together within the same packet header(s). This may provide a mitigation mechanism against linkability attacks on communicating E2E peer WTRUs.

In examples, the application layer ID and the IP address/prefix may be changed periodically. The application layer ID and the IP address/prefix may not be replaced by the relay to be isolated on the per-hop since they are not exchanged in the message header. The link modification procedure may be executed with the concerned peer WTRUs during (e.g., before completion of) the LIU procedure between the WTRU and the relay. If IP communication is used, the LIU procedure may be triggered due to the change of application layer ID and IP address/prefix.

In examples, the LIU messages may be modified to add E2E IDs parameters (e.g., add new E2E IDs parameters). The relay may receive E2E IDs (e.g., new E2E IDs) and E2E security IDs (e.g., new E2E security IDs/session key identifiers) from the WTRU in addition to the per-hop L2 IDs (e.g., new per-hop L2 IDs). The relay may change its own relay-specific IDs used on this hop and mapping to the WTRU's IDs (e.g., E2E IDs, E2E security IDs/session key identifiers). The relay may change its per-hop L2 ID. The relay may send back its IDs (e.g., new IDs) to the WTRU.

In examples, E2E links IDs may be isolated on a per-hop basis to keep LIU procedure execution between the WTRU and the relay (e.g., without involving E2E peer WTRUs).

The relay may replace the E2E IDs and E2E security IDs/session key identifiers with relay-specific IDs if forwarding messages on another hop. In examples, E2E link IDs (e.g., E2E IDs and E2E security IDs/session key identifiers) may be specified in the adaptation header. In examples, E2E security IDs/session key identifiers may be specified in the PDCP header.

The LIU procedure may be executed between the WTRU and the relay, on a per-hop basis, without involving the peer WTRUs. In examples, this may prevent a massive exchange of messages that may be incurred using a "conventional link ID update" procedure. The LIU procedure may be executed over the protected management link to allow the exchange of secured messages between the WTRU and the relay.

In examples, link modification messages may be modified to add parameters (e.g., new parameters). The source WTRU may receive an application layer ID (e.g., new application layer ID) and a IP address/prefix (e.g., new IP address/prefix) from the application layer. The source WTRU may trigger the LIU procedure with the relay (e.g., to change the per-hop link and E2E link IDs), since a change of application layer ID may trigger the change of IDs associated with it. The source WTRU may trigger a link modification procedure with the concerned E2E peer WTRUs (e.g., to inform them about its new application layer ID and possibly new IP address/prefix) prior to the completion of the LIU procedure with the relay, for example.

E2E link IDs may be isolated on a per-hop basis. The relay may replace the L2 IDs identifying the per-hop link with other relay-specific per-hop IDs. The relay may replace the E2E IDs specified in the adaptation header with relay-specific E2E IDs (e.g., when forwarding messages). For example, E2E WTRUs may identify the target WTRU by specifying a relay-specific E2E ID in the adaptation header (e.g., when sending message(s)).

Security information may be replaced by the relay (e.g., since it is transported in the cleartext in the header of each message). Replacing the security information before forwarding a message may enable the relay to isolate (e.g., completely isolate) the E2E link IDs between the WTRU and the relay. This may limit the periodic change of IDs on a per-hop basis, for example, without involving peer WTRUs.

Security IDs/session key identifiers (e.g., MSBs/LSBs of Knrp-sess ID) may be exchanged between E2E peer WTRUs, for example, during the E2E PC5 unicast link establishment. For example, the source WTRU may send a DCR message with the MSBs of Knrp-sess ID specified in the payload of the message and the peer WTRU may reply by sending a DSM Command message that includes the LSBs of Knrp-sess ID in the payload. At this point (e.g., during the sending of these two messages), the security information may not be specified in the header of the messages. The security information may not be accessible at the relay.

In examples, the relay may not have access to the MSBs/LSBs of Knrp-sess ID. The relay may not be able to replace the MSBs/LSBs of Knrp-sess ID before forwarding the DCR/DSM Command messages. The E2E peer WTRUs may receive and locally keep their E2E peer security IDs. The E2E peer WTRUs may be involved in the identifier update.

In examples with direct re-keying, the E2E WTRUs may update their Knrp-sess keys locally and exchange their MSBs/LSBs of Knrp-sess ID (e.g., new MSBs/LSBs of Knrp-sess ID) within the payload of the Direct Re-keying Request (DRR) and DSM Command messages. The relay may not have access to the MSBs/LSBs of Knrp-sess ID. The relay may not be able to replace the MSBs/LSBs of Knrp-sess ID before forwarding the DRR/DSM Command messages.

The E2E peer WTRUs may specify the E2E MSBs/LSBs of Knrp-sess ID in the adaptation header when sending DCR, DRR, or DSM Command messages (e.g., to enable the replacement of E2E MSBs/LSBs of Knrp-sess ID at the Relay). The E2E peer WTRUs may specify (e.g., may also specify) the E2E MSBs/LSBs of Knrp-sess ID in the payload (e.g., when sending DCR, DRR, or DSM Command messages). These examples may enable the relay to replace the E2E MSBs/LSBs of Knrp-sess ID with relay-specific MSBs/LSBs values when forwarding messages. A WTRU may decide to send a message which may be forwarded by a relay (e.g., a message that may only be forwarded by a relay). Such a message may be one that a receiving WTRU may not consider. In this case, a for relay indication (e.g., a relay only indication) may be specified in the message (e.g., payload or header) and the E2E security IDs/session key identifiers may be specified in the adaptation header (e.g., only in the adaptation header and not in the payload).

The E2E peer WTRUs receiving DCR, DRR, or DSM Command messages, with security IDs/session key identifiers specified (<NUM>) in the payload and (<NUM>) in the adaptation header, may determine which values of the security IDs should be used (e.g., from the adaptation header or the payload) by verifying if the message has been received directly from the peer WTRU or if the message has been received via a relay. If the message is received directly from the peer WTRU, then the receiving WTRU may use the security IDs as specified in the payload. If the message is received via a relay, the receiving WTRU may use the security IDs as specified in the adaptation header and may not consider the information received in the payload. The Access Stratum (AS) layer may pass the information specified in the adaptation header (e.g., security IDs/session key identifiers, E2E IDs) to the ProSe layer when PC5 messages are received (e.g., DCR, DRR, DSM Command messages). The security IDs/session key identifiers specified in the adaptation header (e.g., with DCR, DRR, DSM Command messages) may continue to be sent in the adaptation header with other PC5-S messages or data messages over a PC5 unicast link, and/or they may be specified in the PDCP header. The ProSe layer on the E2E WTRUs may pass the security IDs/session key identifiers (e.g., MSBs/LSBs of Knrp-sess ID as received/specified onto the adaptation header with the DCR/DRR and DSM Command messages) to the AS layer.

<FIG> shows an example of E2E link establishment (e.g., via relay and forwarding). One or more of the actions illustrated may be performed. This may include replacement of E2E IDs and per-hop L2 IDs at the relay (e.g., relay WTRU). The parameters shown in bold may be replaced by the relay (e.g., relay WTRU). Parameters above the arrows may show the per-hop L2 IDs. Parameters below the arrows may show the E2E IDs (e.g., E2E L2 IDs, E2E security IDs/session key identifiers) specified in the adaptation header and PDCP header.

At <NUM>, WTRU1 may broadcast a DCR message (e.g., a first message). WTRU1 may specify WTRU1-L2-ID as the source ID for the per-hop link. WTRU1 may specify BCAST (e.g., a broadcast value) as the destination ID for the per-hop link. WTRU1 may generate and specify an E2E ID (e.g., e2e-WTRU1-ID) in the adaptation header. WTRU1 may generate and specify MSBs of Knrp-sess ID (e.g., a session key identifier) in the adaptation header. The MSBs of Knrp-sess ID for WTRU1 may be indicated by the DCR message (e.g., may be put in the payload of the DCR message), for example, in case the message may be directly received from a peer WTRU (e.g., not received via a relay). In this case (e.g., in cases for direct communication), the peer WTRU may not look at the adaptation header. BCAST may be specified in the adaptation header for the E2E destination ID (e.g., or the E2E destination ID may be unspecified, which may imply for all WTRUs), for example, since the message may be for broadcast and not destined to a specific WTRU.

WTRU1 may specify the MSBs of Knrp-sess ID in the adaptation header (e.g., only in the adaptation header and not in the payload) if it adds an indication (e.g., for-relay-only). This means that the DCR message may be processed (e.g., may only be processed) by a relay (e.g., relay WTRU) (e.g., not for direct communication).

WTRU1 may want to send a broadcast DCR message via a specific relay (e.g., a relay WTRU), using an existing per-hop link. The E2E destination in the adaptation header, for example, in this case, may be set to BCAST while the per-hop destination ID may be set to this specific relay per-hop ID. WTRU1 may, for example, select the relay (e.g., relay WTRU) to be used for communication with responding WTRUs (e.g., WTRU2).

In examples, WTRU1 may already know its peer WTRU's E2E ID and may send a message to this specific WTRU. The specific WTRU's E2E ID, for example, may be specified in the adaptation header.

At <NUM>, the relay (e.g., relay WTRU) may receive the broadcasted DCR message and replace the per-hop source ID with a newly allocated one (e.g., R-L2-IDx). The relay (e.g., relay WTRU) may replace the source E2E ID and MSBs of Knrp-sess ID, specified in the adaptation header, with relay specific IDs (e.g., relay E2E ID and relay MSBs) mapping to the E2E ID and the MSBs of Knrp-sess ID (e.g., the session key identifier) for WTRU1 (e.g., R-e2e1-ID and R-e2e1-MSBs of Knrp-sess ID). The relay (e.g., relay WTRU) may add (e.g., may also add) its RID (e.g., in the adaptation layer). The relay may send a second message (e.g., may re-broadcast the DCR message) (e.g., many relays may receive the message and re-broadcast it) indicating the relay specific IDs (e.g., R-e2e1-ID and R-e2e1-MSBs of Knrp-sess ID). In this case, the responding WTRU (e.g., WTRU2) may select the relay to be used for communication with WTRU1.

If the relay (e.g., relay WTRU) receives a DCR message which is not broadcasted (e.g., sent on an existing per-hop link between WTRU1 and the relay (e.g., relay WTRU)), the relay (e.g., relay WTRU) may look at the destination ID specified in the adaptation header. If destination ID is BCAST or if nothing is specified as the E2E destination ID, the relay (e.g., relay WTRU) may have behavior as described above. For example, the relay (e.g., relay WTRU) may allocate itself a per-hop ID to re-broadcast the message (e.g., source per-hop ID) and may replace e2e-WTRU1-ID and e2e-WTRU1-MSBs of Knrp-sess ID with relay specific IDs/session key identifiers.

If the DCR message is sent to a specific E2E peer WTRU ID, the relay may search in its mapping table if a per-hop link already exists and is associated with the specified destination E2E WTRU ID. If such a per-hop link exists, the message may be forwarded over this per-hop link with the relay-specific per-hop ID. If such a per-hop link does not exist, the message may be forwarded as a broadcast in the per-hop destination ID and specific E2E WTRU ID as the destination in the adaptation header.

At <NUM>, WTRU2 may receive the DCR message. The AS layer may pass the E2E IDs specified in the adaptation layer, the MSBs of Knrp-sess ID, and the RID to the ProSe layer (e.g., together with the DCR message). WTRU2 may verify if the message has been received from a relay (e.g., relay WTRU). In examples, WTRU2 may keep track of the MSBs of Knrp-sess ID value as specified in the adaptation header and not the MSBs value from the payload. WTRU2 may verify if it already has a per-hop link established with this relay (e.g., relay WTRU). If not, WTRU2 may first establish a management link with this relay (e.g., relay WTRU) and trigger the authentication procedure, for example, to authenticate the relay (e.g., relay WTRU) and be authenticated by the relay (e.g., relay WTRU).

If the relay authentication fails while establishing the management link, WTRU2 may drop the received DCR message.

If a specific E2E ID is specified as the destination in the adaptation header, WTRU2 may verify if this E2E ID is its own E2E ID (e.g., a previous E2E ID used with WTRU1). If not, WTRU2 may drop the DCR message.

If WTRU2 receives the message (e.g., DCR) directly from WTRU1 (e.g., not from a relay), then WTRU1 may use the MSBs of Knrp-sess ID value specified in the payload. In this case, the values specified in the adaptation layer and in the payload may be identical.

At <NUM>, if the management link is established, WTRU2 may reply to WTRU1 by triggering the authentication procedure via the relay (e.g., relay WTRU). WTRU2 may include the RID in the authentication message. WTRU2 may allocate an e2e-WTRU2-ID, which may be specified in the adaptation header (e.g., together with the received R-e2e1-ID). A per-hop link may be established with the relay (e.g., relay WTRU) at the same time (e.g., WTRU2 may allocate a per-hop L2 ID and reply to the relay's per-hop L2 ID). The relay (e.g., relay WTRU) may forward the authentication message to WTRU1 via the per-hop link (e.g., it may allocate a R-L2-IDy and replace the source and target IDs with WTRU1-L2-ID and R-L2-IDy). The IDs in the adaptation header may be replaced with e2e-WTRU1-ID (e.g., previously received from WTRU1) and R-e2e2-ID (e.g., relay allocated ID mapping to WTRU2). WTRU1 may reply (e.g., may later reply) to the authentication message via the per-hop link with the relay (e.g., relay WTRU).

At <NUM>, WTRU1 may receive the authentication message. AS layer may pass the E2E IDs specified in the adaptation layer and the RID to the ProSe layer (e.g., together with the message). WTRU1 may keep track of the information received in the header and the message. WTRU1 may verify if it already has a management link. If not, WTRU1 may trigger the management link establishment and run the authentication procedure with this relay (e.g., relay WTRU).

In examples, the management link may be established after the authentication procedure is completed successfully (e.g., after <NUM> or <NUM>).

At <NUM>, if the management link is established, WTRU1 may reply to WTRU2 (e.g., it may send an authentication response via the per-hop link with the relay and specify its e2e-WTRU1-ID and R-e2e2-iD in the adaptation header). The relay (e.g., relay WTRU) may look at the destination ID specified in the adaptation header and find the related mappings entry. The relay (e.g., relay WTRU) may replace the IDs in the adaptation header with these values (e.g., e2e-WTRU2-ID and R-e2e1-ID) and forward the message to WTRU2.

At <NUM>, WTRU2 may trigger the security establishment procedure with WTRU1 via the relay (e.g., the relay WTRU). WTRU2 may generate LSBs of Knrp-sess ID (e.g., the session key identifier) and specify it in the adaptation header (e.g., in addition to putting it in the payload of the message). R-e2e1-ID and e2e-WTRU2-ID may be specified (e.g., may also be specified) in the adaptation header. R-e2e1-MSB of Knrp-sess ID, which may be received in the DCR message, may be specified in the PDCP header. WTRU2 may send the DSM command message (e.g., a third message) to the relay (e.g., the relay WTRU) via the per-hop link.

R-e2e1-MSB of Knrp-sess ID, which may be received on the DCR message, may instead, or in addition, be specified in the adaptation header.

At <NUM>, the relay (e.g., the relay WTRU) may forward the DSM command message (e.g., the third message) to WTRU1 and replace the per-hop IDs with the IDs used with WTRU1. The relay may replace (e.g., may also replace) the IDs specified in the adaptation header and IDs specified in the PDCP header with relay specific IDs (e.g., relay LSBs) mapping to WTRU2. e2e-WTRU2-ID may be replaced with Re2e2-ID and R-e2e1-ID may be replaced with e2e-UE1-ID. The relay may generate a relay-specific ID (e.g., a new relay-specific ID), for example, that may be associated with (e.g., may replace) WTRU2 LSBs of Knrp-sess ID (e.g., R-e2e2-LSBs of Knrp-sess ID). The relay LSBs of Knrp-sess for WTRU2 may be indicated in the PDCP header (or in the adaptation header) of the DSM command message.

The relay (e.g., relay WTRU) may ensure that the relay-specific LSBs of Knrp-sess ID replacing WTRU2's LSBs of Knrp-sess ID are unique. For example, the relay (e.g., relay WTRU) may ensure that the relay-specific LSBs of Knrp-sess ID have not been used to replace the ID of another WTRU (e.g. WTRU3) replying (e.g., also replying) to WTRU1's DCR message.

The relay (e.g., relay WTRU) may generate a relay-specific (e.g., a new relay-specific ID) LSBs of Knrp-sess ID if receiving a message from WTRU2 specifying LSBs (e.g., new LSBs) of Knrp-sess ID value in the adaptation layer (e.g., a new DSM command message may be sent as a response to a DSM reject message or to update the IDs periodically).

At <NUM>, WTRU1 may receive the DSM command message. AS layer may pass the E2E IDs specified in the adaptation layer, the LSBs of Knrp-sess ID, and/or the RID to the ProSe layer (e.g., together with the message). WTRU1 may keep track of the LSBs of Knrp-sess ID value as specified in the adaptation header, for example, and not the LSBs values from the payload. WTRU1 may keep (e.g., may also keep) track of the received E2E IDs in the adaptation header and reply by sending a DSM complete message via the per-hop link with the relay (e.g. relay WTRU). The adaptation header may include e2e-WTRU1-ID and R-e2e2-ID. The MSBs of Knrp-sess ID and LSBs of Knrp-sess ID (e.g., e2e-WTRU1-MSBs of Knrp-sess ID and R-e2e2-LSBs of Knrp-sess ID) may be specified in the PDCP header (e.g., or may instead, or in addition, be specified in the adaptation header).

WTRU1 may check if the received LSBs of Knrp-sess ID (e.g., R-e2e2-LSBs of Knrp-sess ID) may be unique. For example, the WTRU1 may check that the same LSBs of Knrp-sess ID, which may be locally associated with the MSBs of Knrp-sess ID, have not been received already by another WTRU and/or another relay (e.g., relay WTRU). If the received LSBs of Knrp-sess ID are not unique, WTRU1 may send a DSM reject message.

The relay (e.g., relay WTRU) may generate a relay-specific (e.g., a new relay-specific) MSBs of Knrp-sess ID if receiving a message from WTRU1 specifying a new MSBs of Knrp-sess ID in the adaptation header. For example, the relay (e.g., relay WTRU) may specify MSBs of Knrp-sess ID (e.g., new MSBs of Knrp-ness ID) values in the adaptation layer (e.g., a DSM complete message may be sent to update the IDs periodically).

At <NUM>, the relay (e.g., relay WTRU) may replace WTRU1's IDs with its relay-specific IDs mapping to WTRU1. The relay (e.g., relay WTRU) may replace the relay-specific IDs mapping to WTRU2 with WTRU2's IDs and forward the message to WTRU2, for example, via the per-hop link with WTRU2.

At <NUM>, WTRU2 may receive the DSM complete message. The WTRU2 may complete the E2E PC5 unicast link establishment, for example, by sending a DCA message. The message may be sent via the per-hop link with the relay (e.g., relay WTRU) and include IDs in the adaptation header to identify WTRU1. The MSBs/LSBs of Knrp-sess ID may be specified in the PDCP header (e.g., e2e-UE2-LSBs of Knrp-sess ID and R-e2e1-MSBs of Knrp-sess ID).

At <NUM>, the relay (e.g., relay WTRU) may replace WTRU2's IDs with its relay-specific IDs mapping to WTRU2. The relay (e.g., relay WTRU) may replace the relay-specific IDs mapping to WTRU1 with WTRU1's IDs and forward the message to WTRU1, for example, via the per-hop link with WTRU1.

At <NUM>, E2E PC5 unicast link may be established between WTRU1 and WTRU2 via the relay (e.g., relay WTRU). The link may be secured E2E. Identifiers for the per-hop links and E2E link may be unique (e.g., may all be unique) per per-hop link. For example, the relay (e.g., relay WTRU) may replace IDs (e.g., all IDs), for example, before forwarding them to isolate the E2E links on a per-hop basis.

At <NUM>-<NUM>, WTRU1/WTRU2 may exchange data via the relay (e.g., relay WTRU). The relay (e.g., relay WTRU) may replace the IDs based on its mapping table before forwarding them. The messages may be secured E2E. WTRU1 may locate the corresponding Knrp-sess ID locally using e2e-WTRU1-MSBs of Knrp-sess ID concatenated with R-e2e2-LSBs of Knrp-sess ID while WTRU2 may locate the corresponding Knrp-sess ID locally using R-e2e1-MSBs of Knrp-sess ID concatenated with e2e-WTRU2-LSBs of Knrp-sess ID. In examples, at <NUM>, the relay (e.g., the relay WTRU) may receive a fourth message from WTRU1. The fourth message may indicate data (e.g., a first data) to be sent to WTRU2, indicate relay LSBs (e.g., Re2e2-LSBs of Knrp-sess), and indicate MSBs for WTRU1 (e.g., e2e-WTRU1-MSBs of Knrp-sess ID). In examples, at <NUM>, the relay (e.g., the relay WTRU) may send a fifth message to WTRU2. The fifth message may indicate data (e.g., the first data) to be sent to WTRU2, indicate relay MSBs (e.g., R-e2e1-MSBs of Knrp-sess ID), and indicate LSBs for WTRU2 (e.g., e2e-WTRU2-LSB of Knrp-sess ID). In examples, at <NUM>, the relay (e.g., the relay WTRU) may receive a sixth message from WTRU2. The sixth message may indicate data (e.g., a second data) to be sent to the WTRU1, indicate relay MSBs (e.g., R-e2e1-MSBs of Knrp-sess ID), and indicate LSBs for WTRU2 (e.g., e2e-WTRU2-LSB of Knrp-sess ID). In examples, at <NUM>, the relay (e.g., the relay WTRU) may send a seventh message to WTRU1. The seventh message may indicate data (e.g., the second data) to be sent to WTRU1, indicate relay LSBs (e.g., R-e2e2-LSBs of Knrp-sess), and indicate MSBs for WTRU1 (e.g., e2e-WTRU1-MSBs of Knrp-sess ID).

A LIU procedure via a management link may be performed. If a trigger for privacy occurs on a WTRU, the LIU procedure may be re-used between the WTRU and the relay (e.g., relay WTRU) to update identifiers (e.g., all identifiers) used on the per-hop link. For example, the identifiers used over this per-hop link may be the per-hop IDs and E2E link IDs (e.g., all E2E link IDs such as E2E IDs and E2E security IDs/session key identifiers). A privacy timer may be started on a per-hop link establishment basis or on an E2E link establishment basis.

Source/destination L2 IDs and security IDs/session key identifiers (e.g., new source/ destination L2 IDs and security IDs/session key identifiers), such as MSBs and LSBs of Knrp-sess ID, may be generated and exchanged between peer WTRUs using the LIU messages. The LUI messages may be designed for direct PC5 unicast link (e.g., designed only for direct PC5 unicast link). To support the change of identifiers for E2E PC5 unicast links, the LIU messages may be modified to carry the per-hop link IDs, E2E link IDs, and/or a request number. The E2E ID (e.g., new E2E ID) and security IDs/session key identifiers (e.g., new security IDs/session key identifiers such as MSBs or LSBs of Knrp-sess ID) may be specified (e.g., may also be specified) in the message. If multiple E2E link IDs are changed, multiple E2E IDs and E2E security IDs/session key identifiers may be specified in the LIU messages. The LIU messages may be modified to include: the current per-hop link IDs, the WTRU per-hop ID (e.g., WTRU new per-hop ID), a list of {current E2E IDs, associated security IDs/session key identifiers, WTRU E2E ID (e.g., WTRU new E2E ID), and/or WTRU security IDs/session key identifiers (e.g., WTRU new security IDs/session key identifiers)} and/or a number. The WTRU security IDs/session key identifiers (e.g., new security IDs/session key identifiers) may be the MSBs or LSBs of Knrp-sess ID, depending on if the WTRU has initiated the link establishment (e.g., has sent the DCR message to establish the E2E link) or if the WTRU has responded to the DCR message.

The relay (e.g., the relay WTRU) may find the specified per-hop entry, for example, from its mapping table. The relay (e.g., relay WTRU) may find the specified E2E links, and change the relay-specific IDs/session key identifiers used with the WTRU and mapped to E2E peer WTRUs, e.g. R-e2e2-ID and R-e2e2-LSBs of Knrp-sess ID. This may be done for multiple E2E peer WTRUs. The relay (e.g., relay WTRU) may change (e.g., may also change) its per-hop L2 ID used with the WTRU.

If the WTRU initiating the LIU procedure has E2E unicast links (e.g., many unicast links) established via the relay (e.g., relay WTRU), the WTRU may send multiple LIU request messages to the relay (e.g., relay WTRU). The relay (e.g., relay WTRU) may handle the multiple LIU request messages, for example, in this case. The relay (e.g., relay WTRU) may change its related IDs and replies with an LIU response message, for example, for each of the received LIU request messages. If IDs (e.g., all IDs) are changed, the WTRU which initiated the procedure may send an LIU Ack message. The LIU Ack may acknowledges response messages (e.g., all response messages). A number may be added to the Ack message to indicate the number of responses that are acknowledged. The relay (e.g., relay WTRU) may validate that the received number is correct, (e.g., corresponds to the number of responses sent) and if the number is not correct, the relay (e.g., relay WTRU) may retransmit the response messages or release the per-hop link or E2E link that have not been acknowledged.

<FIG> shows an example of a LIU procedure isolated on a per-hop link basis. One or more of the actions illustrated may be performed. Instead or in addition to the number of responses that are acknowledged, a list of numbers may be specified in the Ack message (e.g., each request message may be associated with a number that is repeated in the response message).

The LIU procedure may be run between the WTRU and the relay using the management link. The messages may be modified to indicate that the LIU applies to another link (e.g., not the management link per se).

Since the identifiers that are changed may be known (e.g., may only be known) by the WTRU and the relay, E2E peer WTRUs may not be (e.g., may not need to be) involved in this procedure.

At <NUM>, WTRU1 may have a per-hop link with the relay and may have an E2E PC5 unicast link established with WTRU2 and possibly other WTRUs not shown in <FIG>. WTRU1 may have (e.g., may also have) a management link established with the relay. This management link may be a PC5 unicast link with security enabled (e.g., with integrity and confidentiality protection). WTRU2 may have (e.g., may also have) a per-hop link and a PC5 unicast management link established with the relay.

At <NUM>, WTRU1 may receive a privacy trigger. The privacy trigger may be related to a relay ID, a specific per-hop link, or a specific E2E unicast link. WTRU1 may generate a per-hop ID (e.g., a new per-hop ID). For E2E links (e.g., all E2E links) going through the specific relay, WTRU1 may generate an E2E ID (e.g., new E2E ID) and a portion (e.g., a new portion) of the security IDs/session key identifiers. For the security IDs/session key identifiers, WTRU1 may generate MSBs (e.g., a new MSBs) or LSBs (e.g., new LSBs) of the Knrp-sess ID, depending on if WTRU1 has previously generated the MSBs or LSBs. WTRU1 may send a LIU request message to the relay via the management link. WTRU1 may indicate that the request applies to a specific per-hop link. The source/destination IDs for the per-hop link may be specified in the LIU request message with the WTRU1 per-hop ID (e.g., the new WTRU1 per-hop ID). E2E specific information may be specified (e.g., may also be specified) in the LIU request message. The E2E specific information may include one or more of the following: the current source/destination E2E IDs, the WTRU1 E2E ID (e.g., new WTRU E2E ID), and the WTRU1 security IDs/session key identifiers portion (e.g., new MSBs of Knrp-sess ID). WTRU1 may include (e.g., may also include) a number to identify this message. The number may be a sequence number or a random number, for example.

If WTRU1 has established multiple E2E links via this relay (e.g., transported via the same per-hop link), these E2E IDs (e.g., all these E2E IDs) may be changed (e.g., may also be changed). Multiple E2E specific information may be included on the message.

The number of E2E links included in the message may be specified. An indication about subsequent request messages to be sent may be specified (e.g., more indication).

At <NUM>, the relay may receive the message, fetch the specific per-hop link and E2E links information, and update its mapping table with the WTRU1 IDs (e.g., the new WTRU1 IDs), for example, while keeping the current values. The relay may generate IDs (e.g., new IDs) to change its per-hop ID and the E2E relay-specific IDs/session key identifiers mapping to peer WTRUs (e.g., mapping to WTRU2). The relay may send back the LIU response message. The LIU response message may include its ID (e.g., new ID) for the per-hop link, its relay-specific E2E ID (e.g., new relay-specific E2E ID), and a portion (e.g., new portion) of the security IDs/session key identifiers, such as MSBs or LSBs of Knrp-sess ID (e.g., new MSBs or LSBs of Knrp-sess ID). The number, as received on the request message, may be repeated on the response message.

If multiple E2E IDs were specified in the request message, the relay may include the corresponding E2E IDs (e.g., same corresponding E2E IDs) in the response message.

If a "more" indication was specified on the request message, the relay may expect to receive another LlU request message.

At <NUM>, if WTRU1 changes its IDs related to multiple E2E links, the list of E2E IDs may be sent via multiple request messages (e.g., one E2E link IDs per request message or multiple per request message, with a maximum number per request message). A number (e.g., new number) may be used if sending this message. WTRU1 per-hop link ID may have been changed at <NUM> and may not be included in this subsequent request message.

At <NUM>, if the relay receives a subsequent request message, it may behave as described in <NUM>. The number as received on the request at <NUM> may be used on the response message. WTRU2 per-hop link ID may have been changed at <NUM> and may not be included in this subsequent request message.

At <NUM>, WTRU1 may validate that the received number matches the number that it has previously sent. WTRU1 may update its table with the IDs (e.g., new IDs) received. WTRU1 may validate (e.g., may also validate) that an LIU response message has been received for LIU request messages (e.g., all LIU request messages) sent. WTRU1 may send an LIU Ack message including the per-hop link IDs and the last number sent/received on the request/response messages, for example, in this case, if a sequence number was used. The list of numbers may (e.g., may instead) be specified (e.g., if a random number was used). The list of E2E link IDs that were updated may (e.g., may also) be specified (e.g., may be included in the transmitted messages, added as parameters to the LIU Ack message, etc.) and their corresponding new values may (e.g., may also) be specified (e.g., may be included in the transmitted messages, added as parameters to the LIU Ack message, etc.).

Application layer and IP address/prefix changes may be performed. Isolating the IDs (e.g., per-hop IDs, E2E IDs, E2E security IDs/session key identifiers) on a per-hop basis may limit the change of these IDs between the WTRU and the relay. The application layer ID and IP address/prefix, if IP communication is used, may need to be changed (e.g., periodically).

To support the change of application layer ID and IP address/prefix, the link modification procedure may be modified to allow sending the source WTRU application layer ID (e.g., new application layer ID) and IP address/prefix (e.g., new IP address/prefix), if IP communication is used, to the concerned E2E peer WTRUs. The link modification procedure may be run with the E2E peer WTRUs aware of this application layer ID, and possibly IP address/prefix.

Using the isolation of IDs (e.g., as described herein) may be used to limit the change of application layer ID and IP address/prefix to the source WTRU (e.g., the E2E peer WTRU may not need to change its application layer ID and IP address/prefix). For example, a reason to limit this change to the source WTRU may be that the change of IDs on both WTRUs, (e.g., at the same time), may have been required because of a linkability issue (e.g., which may not apply in this case).

The linkability issue may arise, for example, if the source WTRU IDs that are sent in cleartext are changed while the peer WTRU IDs, sent (e.g., also sent) in cleartext, are not changed. Since these IDs may be visible and if the source WTRU IDs (e.g., only the source WTRU IDs) are changed, a malicious WTRU may link the source WTRU IDs (e.g., source WTRU new IDs) with the old source WTRU IDs by referring to the peer WTRU IDs that have not changed. Both WTRUs may change their IDs at the same time to avoid this linkability issue.

The IDs sent in cleartext may be changed (e.g., may all be changed) between the WTRU and the relay using the per-hop isolation of IDs (e.g., in this case). The application layer ID and IP address/prefix may not be sent in cleartext and no linkability issue may be observed if the source WTRU changes them (e.g., if only the source WTRU changes them).

If the application layer ID and possibly IP address/prefix are changed on a source WTRU, this WTRU (e.g., the source WTRU) may find per-hop links (e.g., all per-hop links) with which these IDs have been used. The LIU procedure may be run for these links (e.g., all these links). The concerned peers may be informed of the IDs (e.g., new IDs), for example, using the link modification procedure.

<FIG> illustrates an example procedure if the application layer ID and IP address/prefix are changed on the source WTRU. <FIG> may illustrate support of application layer ID and IP address/prefix change related to PC5 unicast links, for example, established via WTRU-to-WTRU relay. One or more of the actions illustrated may be performed.

At <NUM>, WTRU1 may have a per-hop link with the relay (e.g., relay WTRU) and may have an E2E PC5 unicast link established with WTRU2. WTRU1 and WTRU2 may have (e.g., may also have) a management link established with the relay (e.g., relay WTRU). This management link may be a PC5 unicast link with security enabled (e.g., at least encryption).

At <NUM>, WTRU1 may receive a trigger to change its application layer ID and IP address/prefix (e.g., it may receive a new application layer ID and a new IP address/prefix, if IP communication is used, from the application layer).

WTRU1 may send an LIU request message (e.g., a fourth message) to the relay (e.g., relay WTRU) indicating per-hop IDs (e.g., new per-hop IDs) and E2E link information. E2E link information may include E2E IDs and E2E security IDs (e.g., MSBs/LSBs of Knrp-sess ID) for E2E (e.g., all E2E) unicast links with this relay. The LIU message may indicate a request to update stored E2E link information associated with an E2E link and with MSBs/LSBs (e.g., a first set of MSBs and a first set of relay LSBs) of Knrp-sess ID (e.g., the session key identifier). The LIU message may indicate a second set of MSBs of Knrp-sess ID (e.g., new session key identifier) and a E2E ID (e.g., a new E2E ID) for WTRU1. The relay (e.g., the relay WTRU) may determine a second set of relay LSBs of Knrp-sess ID (e.g., a new session key identifier) and a relay E2E ID (e.g., a new relay E2E ID) for WTRU1.

At <NUM>, the relay (e.g., the relay WTRU) may send the LIU response message (e.g., a fifth message) to WTRU1 with its IDs (e.g., new IDs) for the per-hop link and for the E2E links specified on the LIU request. The LIU response message may indicate the second set of relay LSBs of Knrp-sess ID and relay E2E ID for WTRU1.

At <NUM>, WTRU1 may send a link modification request to WTRU2 with its application layer ID (e.g., new application layer ID) and IP address/prefix (e.g., new IP address/prefix), if IP communication is used. The link modification request message may be modified to support an operation code (e.g., new operation code) for e.g., "change-of-ID" and the application layer ID (e.g., new application layer ID) and IP address/prefix (e.g., new IP address/prefix).

At <NUM>, WTRU2 may send a link modification accept to Ack the IDs (e.g., new IDs) from WTRU1. The IDs (e.g., new IDs) received in the request message may be sent back with the accept message.

At <NUM>, WTRU1 may send a LIU Ack message (e.g., a sixth message) to the relay (e.g., the relay WTRU) (e.g., this may complete the LIU procedure). The LIU Ack message may indicate that WTRU1 received the indication of the second set of relay LSB of Knrp-sess ID and relay E2E ID for WTRU1.

WTRU1 and relay (e.g., relay WTRU) may start using the per-hop L2 IDs (e.g., new per-hop L2 IDs), E2E IDs (e.g., new E2E IDs), and associated security IDs (e.g., new associated security IDs). WTRU1 and WTRU2 may start using WTRU1's application layer ID (e.g., new application layer ID) and IP address/prefix (e.g., new IP address/prefix).

Examples of a compatible direct/indirect link establishment request are provided herein.

A WTRU (e.g., WTRU1) may trigger the link establishment procedure if: WTRU1 wants to announce its supported service(s); and/or WTRU1 wants to establish a PC5 unicast link with a specific target WTRU. WTRU1 may allow direct and/or indirect (e.g., via a relay) communication for the advertised services. In examples, the WTRU1 may send a regular DCR message for direct communication (e.g., without an adaptation header, for example, not used at relays) to advertise its services. In examples, the WTRU1 may send an indirect DCR message (e.g., with adaptation layer) so that relays may forward the DCR message. The WTRU1 may not know if the target WTRU is reachable directly or via a relay and may allow both possibilities. In examples, the WTRU1 may send (e.g., first send) a DCR message (e.g., a regular DCR message) for direct communication. In examples, if no response is received from the target WTRU, the WTRU1 may send a DCR message (e.g., another DCR message, including adaptation layer) that may be forwarded by relays.

In examples where the direct/indirect procedures use a different DCR message format, a two part procedure may be used. WTRU1 may send DCR messages (e.g., two DCR messages) advertising the same information. The difference (e.g., the only difference) between the DCR messages (e.g., two DCR messages) may be that one message includes an adaptation header and the other one does not. Having this two part procedure may generate more PC5 signaling from WTRU1 and may delay the link establishment via the relay when the target WTRU may be reachable (e.g., may only be reachable) via a relay.

Examples of minimizing and/or limiting PC5 signaling during link establishment when both direct/indirect communication may be allowed are provided herein. Examples of making link establishment via a relay with a known target WTRU more efficient are provided herein.

In examples with direct communication, a PC5 unicast link may be identified (e.g., uniquely identified) using the pair of source WTRU L2 ID and target WTRU L2 ID. In examples with indirect communication (e.g., via a relay and using an adaptation header), if a WTRU receives a message from the relay, the adaptation header may include the E2E peer WTRU ID (e.g., the E2E peer WTRU ID only, not the WTRU's E2E ID).

Using the pair of L2 IDs with direct communication may provide the ability to locate (e.g., uniquely locate) a unicast link even in the case where two peer WTRUs use the same L2 ID. In examples, the WTRU may not know to which E2E PC5 link the message is associated if the peer WTRU's E2E ID (e.g., if only the peer WTRU's E2E ID) is included in the adaptation header.

In examples, WTRU1 may send a DCR message without an adaptation header. A relay may receive the DCR message and may add an adaptation header to the DCR message before forwarding it. A first target WTRU may receive the DCR message directly from WTRU1 and may establish a direct unicast link with WTRU1. A second target WTRU may receive the DCR message via the relay and may establish an indirect unicast link with WTRU1. A WTRU may use the E2E security context ID (e.g., Knrp-sess ID) to identify (e.g., uniquely identify) the E2E link when receiving a PC5 message, for example, which may include information (e.g., may only include information) identifying the peer WTRU.

<FIG> illustrates an example compatible direct/indirect PC5 unicast link establishment procedure. To make the link establishment procedure more efficient and to reduce the PC5 signaling, a single part procedure may be used. For example, a DCR message (e.g., a single DCR message) may be used for direct and indirect link establishment procedures. To enable a single part procedure for direct and indirect link establishment procedure with integrated discovery, an initiating WTRU (e.g., WTRU1) may send a DCR message without an adaptation header. A second WTRU (e.g., WTRU2) may receive the DCR message and establish a direct unicast link with the initiating WTRU. A relay WTRU may receive the DCR message, without an adaptation header, and may add an adaptation header to the DCR message before forwarding it. A third WTRU (e.g., WTRU3) may receive the DCR message via the relay and may establish an indirect unicast link with the initiating WTRU.

A WTRU (e.g., WTRU1) may receive a message with an adaptation header, which may include (e.g., may only include) information identifying the peer WTRU ID (e.g., WTRU3 E2E ID) (e.g., may not include WTRU1 E2E ID) and may use the E2E security context ID (e.g., Knrp-sess ID) to identify (e.g., uniquely identify) the E2E link. In examples, the security context ID may be passed to the ProSe layer if a PC5 message is received. Receiving the peer WTRU E2E ID (e.g., only the peer WTRU E2E ID) may not be enough for WTRU1 to identify (e.g., uniquely identify) the E2E link, for example, in the case where the same E2E ID may be used for WTRU3 and <NUM>.

In examples, the WTRU1 may send a DCR message without an adaptation header. The WTRU1 may specify its layer-<NUM> ID (WTRU1 L2 ID) in the message header.

In examples, the relay may receive the DCR message and may add an adaptation header before forwarding the message. The relay may generate a relay-specific E2E ID (e.g., relay-specific ID1) as WTRU1 E2E ID and may keep the mapping with WTRU1 L2 ID as received on the DCR message. The relay may (e.g., may also) generate relay-specific MSBs of Knrp-sess ID and may keep the mapping with the MSBs of Knrp-sess ID provided by WTRU1 in the message payload. The relay-specific ID1 and relay-specific MSBs of Knrp-sess ID may be put in the adaptation header (e.g., as specified in <FIG> at <FIG>). In examples, the relay may use WTRU1 L2 ID received on the DCR message as WTRU1 E2E ID and may put it in the adaptation header instead of the relay-specific ID. In examples, the MSBs of Knrp-sess ID provided by WTRU1 may be put in the adaptation header. For the remainder of the procedure, the MSBs and LSBs of Knrp-sess ID may be treated as specified in <FIG>, for example. In examples, the WTRU2 may receive the DCR message (e.g., directly) from WTRU1 (e.g., receive the DCR message without an adaptation header) and may continue the PC5 unicast link establishment procedure with WTRU1 directly, without adding an adaptation header. The WTRU2 may send a direct communication accept message (e.g., without including an adaptation header). The authentication and/or security procedures may be executed between WTRU1 and WTRU2, if needed, before sending the DCA message (not shown in <FIG>).

In examples, the WTRU3 may receive the DCR message from the relay, which may include an adaptation header. The WTRU3 may continue the PC5 unicast link establishment procedure with WTRU1 indirectly, for example, via the relay. An adaptation header may be specified with the PC5 messages exchanged between WTRU3 and WTRU1 via the relay. If WTRU3 sends a message via the relay, the adaptation header may include the destination ID (e.g., WTRU1 E2E ID) that the WTRU3 has received on the DCR message. The adaptation header may include WTRU3's ID associated to the E2E link, for example, WTRU3 ID (generated by WTRU3). The WTRU3 may send a DCA message for WTRU1 via the relay, for example, including an adaptation header.

In examples, if receiving a message for WTRU1, the relay may remove the destination ID from the adaptation header or replace the destination ID (e.g., WTRU1 E2E ID) with WTRU1 L2 ID in the adaptation header as specified with the DCR message. The relay may save the WTRU1 L2 ID into the relay's mapping table before forwarding the DCR message with WTRU1's E2E ID. The relay may add WTRU3 E2E ID as the source ID in the adaptation header before forwarding the message to WTRU1. The relay may generate a relay-specific ID for WTRU3 (e.g., relay-specific ID3) to be used as WTRU3 E2E ID. In examples, the relay may use WTRU3 L2 ID as WTRU3 E2E ID. The relay may keep the mapping of WTRU3 information (e.g., WTRU3 L2 ID and WTRU3 E2E ID).

In examples, the WTRU1 may support receiving replies for direct or indirect communication (e.g., responses directly from the WTRU2 or from the WTRU3 via the relay). If a response is directly received from a target WTRU (e.g., WTRU2), the WTRU1 may continue the direct link establishment procedure with the target WTRU (e.g., normal PC5 link establishment behavior). In examples, the PC5 messages may not include an adaptation layer. If a response from a target WTRU (e.g., WTRU3) is received via a relay (e.g., including an adaptation header), the WTRU1 may continue the indirect link establishment procedure and communication via this relay. In examples, WTRU1 may receive/send messages which may include an adaptation header. The target WTRU E2E ID (e.g., as received in the adaptation header from the relay, for example, WTRU3 E2E ID) may be specified in the adaptation header if the WTRU1 receives a message via the relay. The WTRU1 may save the mapping between its L2 ID (e.g., source L2 ID used on the DCR message and possibly WTRU1 ID (e.g., generated by WTRU1) which may be used as source E2E ID in the adaptation header if WTRU1 sends a message via the relay) and the target WTRU's info (e.g., WTRU3 E2E ID received in the adaptation header and application layer ID) for this E2E link.

Examples of standalone direct/indirect discovery may be provided herein. In examples when a WTRU communicates with a peer WTRU via a relay, the relay may be able to forward messages between E2E peer WTRUs based on the adaptation layer header content. In examples, the usage of an adaptation layer may be decided by the WTRUs and relay during the indirect link establishment procedure. In examples when a standalone discovery procedure is performed before the indirect link establishment procedure and if the adaptation layer is still decided during the indirect link establishment procedure, the procedure (e.g., the whole procedure) may become inefficient. In examples, broadcast messages may be provided even if WTRU1 has discovered WTRU3 during the discovery procedure. WTRU1 may not specify the discovered WTRU3 E2E ID with the DCR message since no adaptation may be used with the DCR message.

In examples provided herein, the WTRUs/relay may decide during the discovery phase if an adaptation layer header may be used. The WTRUs and relay may use an adaptation layer header decided during the discovery phase for indirect link establishment, which may simplify the indirect link establishment procedure and avoid unnecessary broadcast messages (e.g., the relay may forward a direct communication request to a peer WTRU (e.g., WTRU3) based on adaptation layer, instead of broadcasting it).

Examples during discovery phase may be provided herein. In examples, the ProSe WTRU-to-WTRU relay may receive an announcement message from a target WTRU that may announce its supported application ID. If receiving the announcement message, the relay may assign an E2E ID for the target WTRU (e.g., a relay specific ID or may re-use the target WTRU L2 ID as received with the announcement message) and may broadcast the announcement message with the assigned E2E ID. The assigned E2E ID may be included in the announcement message or in an adaptation layer header.

In examples, the ProSe WTRU-to-WTRU relay may receive a solicitation message from a source WTRU. The solicitation message may include a specific target WTRU ID or an application ID to search for WTRUs (e.g., all WTRUs) running that application. If receiving the solicitation message, the relay may assign an E2E ID for the source WTRU (e.g., a relay specific ID or may re-use the source WTRU L2 ID as received with the solicitation message) and may broadcast the solicitation message with the assigned source WTRU E2E ID. The assigned source WTRU E2E ID may be included in the solicitation message or in an adaptation layer header. If receiving the solicitation message, a target WTRU (e.g., interested in the announced application ID or recognizing its specified target WTRU ID) may respond with a response message and may specify the source WTRU E2E ID received with the solicitation message.

In examples, the relay may receive the response message from the target WTRU. The relay may assign an E2E ID for the target WTRU (e.g., a relay specific ID or may re-use the target WTRU L2 ID). If the solicitation message received by the target WTRU included an adaptation header, the response message may have an adaptation header including the source WTRU E2E ID. If the solicitation message received by the target included no adaptation header, the source WTRU E2E ID may be specified in the response message. The relay may forward the response message to WTRU1 with the assigned target WTRU E2E ID specified either in the adaptation header or into the response message.

In examples when the source and target WTRUs are successfully discovered, the source and target WTRUs may set up a unicast link via the relay using the DCR message (e.g., adding the adaptation layer). The target WTRU E2E ID may already be discovered so WTRU1 may send the DCR message with an adaptation header including the target WTRU E2E ID. The DCR message may be sent to the selected relay.

Examples of a standalone discovery-based procedure may be provided with the assumption that the peer WTRUs may communicate via relay. The relay may be able to forward messages between peer WTRUs based on the adaptation layer header. The WTRU (e.g., target or source) may receive the discovery message from (e.g., directly from) the announcing WTRU or via a relay. In examples, the WTRU may decide to provide direct link establishment or establishment via the relay (e.g., indirect link establishment). The decision may be based on policies or link quality, for example.

Examples based on WTRU-to-WTRU discovery are provided herein. <FIG> illustrates an example of a discovery procedure if an adaptation header is included. As shown in <FIG>, the relay WTRU may add an adaptation header to the announcement message before forwarding it. The target WTRU (e.g., WTRU2) may send an announcement message that may include a supported application ID, for example. WTRU2 may (e.g., may also) include an indication (e.g., relay allowed), indicating if relays may forward the message. The relay may receive the announcement message from WTRU2. The relay may allocate an E2E ID for WTRU2 (e.g., may generate a relay-specific ID or may re-use WTRU2 L2 ID as WTRU2 E2E ID) and may keep the mapping with WTRU2 L2 ID as received with the announcement message from WTRU2. The relay may forward the announcement message with information (e.g., additional information) including the relay ID and WTRU2 E2E ID.

In examples, before forwarding the announcement message, the adaptation header may not be added, and the announcement message may be sent with information (e.g., additional information) in the message. In examples, before forwarding the announcement message, the adaptation header including WTRU2 E2E ID may be added. The relay ID may be added to the adaptation header or to the message.

WTRU1 may initiate the link establishment procedure when receiving the announcement message from WTRU2 via the relay. WTRU1 may send a DCR message via the relay with an adaptation header including WTRU2 E2E ID as received on the announcement message.

The relay may add WTRU1 E2E ID in the adaptation header and may replace WTRU2 E2E ID with WTRU2 ID, based on the information from its mapping table. The relay may forward the DCR message to target WTRU2. A difference with these examples is that in other examples, the DCR message sent by WTRU1 may already include an adaptation header so the relay may modify the information in the adaptation header and may not need to add it. In examples, WTRU2 may complete the link establishment by sending a DCA message which may be forwarded to WTRU1 by the relay.

<FIG> illustrates an example of a discovery procedure when an adaptation header is included. As shown in <FIG>, the target WTRU2 may receive a solicitation message from source WTRU1 via the relay WTRU, where the relay WTRU may add an adaptation header to the solicitation message before forwarding it. WTRU1 may send a solicitation message that may include WTRU2 E2E ID and an application ID for an intended service (e.g., any intended service). The WTRU1 may (e.g., may also) include an indication if relaying is allowed.

The relay, if receiving the solicitation message, may allocate an E2E ID for WTRU1 (e.g. may generate a relay-specific ID or may re-use WTRU1 L2 ID as WTRU1 E2E ID) and may keep the mapping with WTRU1 L2 ID as received with the solicitation message from WTRU1. The relay may broadcast the solicitation message and may act according to one of the following: an adaptation header may not be added for the solicitation message and the solicitation message may be sent with additional information that may include WTRU1 E2E ID and relay L2 ID; or an adaptation header including WTRU1 E2E ID may be added before forwarding the solicitation message.

If the solicitation message received via the relay does not include an adaptation header, then WTRU2 may send a response message including WTRU1 E2E ID. If the solicitation message received via the relay includes an adaptation header, then WTRU2 may send a response message and may add an adaptation header where WTRU1 E2E ID is included.

The relay may generate an E2E ID for WTRU2 and may keep the mapping with WTRU2 L2 ID or may use WTRU2 L2 ID as received on the response message as WTRU2 E2E ID. The relay WTRU may forward the response message to WTRU1. If the solicitation message received via the relay does not include an adaptation header, the relay may include WTRU2 E2E ID in the response message. If the solicitation message received via the relay includes an adaptation header, the relay may put WTRU2 E2E ID in the adaptation header. The relay may replace WTRU1 E2E ID as received by WTRU2 with WTRU1 L2 ID from its mapping table.

In examples, if the discovery procedure is completed, the link establishment procedure may be triggered (e.g., WTRU1 may send a DCR message including WTRU2 E2E ID in the adaptation header and WTRU2 may respond with a DCA message including WTRU1 E2E ID in the adaptation header).

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

Although the implementations described herein may consider 3GPP specific protocols, it is understood that the implementations described herein are not restricted to this scenario and may be applicable to other wireless systems. For example, although the solutions described herein consider LTE, LTE-A, New Radio (NR) or <NUM> specific protocols, it is understood that the solutions described herein are not restricted to this scenario and are applicable to other wireless systems as well.

Claim 1:
A relay wireless transmit/receive unit (WTRU) for establishing an end-to-end (E2E) link, comprising:
a processor configured to:
receive a first message from a first WTRU, wherein the first message comprises an adaptation header that indicates a first set of most significant bits (MSBs) for the first WTRU that are associated with a first session key identifier;
generate a second session key identifier;
generate a second set of MSBs based on the second session key identifier, wherein the second set of MSBs have a mapping to the first set of MSBs;
send a second message to a second WTRU, wherein the second message indicates the second set of MSBs;
generate a first set of least significant bits (LSBs) based on the second session key identifier, wherein the first set of LSBs have a mapping to a second set of LSBs that are associated with the second WTRU; and
send a third message to the first WTRU, wherein the third message indicates the first set of least significant bits (LSBs).