WO2021229382A1

WO2021229382A1 - Service continuity for layer-3 ue-to-network relay

Info

Publication number: WO2021229382A1
Application number: PCT/IB2021/053875
Authority: WO
Inventors: Zhang FU; Shabnam Sultana
Original assignee: Telefonaktiebolaget Lm Ericcson (Publ)
Priority date: 2020-05-15
Filing date: 2021-05-06
Publication date: 2021-11-18

Abstract

A remote UE (301) that is configured to establish a direct connection with a RAN access point, obtain a UE identifier that identifies a relay UE with which the remote UE has a direct connection, and obtain a session identifier that identifies an established session used by the relay UE to relay traffic from the remote UE to a core network function. The remote UE is further configured to transmit, using the direction connection with the RAN access point, a session establishment request. The session establishment request includes: i) the UE identifier that identifies the relay UE, ii) the session identifier that identifies the session used by the relay UE to relay traffic from the remote UE, and iii) a network address that the remote UE received from the relay UE.

Description

SERVICE CONTINUITY FOR LAYER-3 UE-TO-NETWORK RELAY

TECHNICAL FIELD

[001] Disclosed are embodiments related to layer-3 (L3) UE-to-Network (UE-NW) relays.

BACKGROUND

[002] FIG. 1 shows the high level view of the non-roaming 5G System (5GS) architecture for vehicle-to-everything (V2X) communication over the PC5 and Uu reference points. Two user equipments (UEs) can communicate with each other either directly via the PC5 sidelink or they can communicate with each other through the Uu interface and via an application server (AS). A UE is any device (e.g., smartphone, computer, tablet, sensor, appliance, vehicle, etc.) capable of wireless communication with another device (e.g., another UE or an access point, such as a base station).

[003] 3GPP TR 23.752 V0.3.0 solution #6 describes the basic idea of the Layer-3 UE- to-Network relay. As described in TR 23.752, the ProSe 5G UE-to-Network Relay entity provides the functionality to support connectivity to the network for Remote UEs. The ProSe 5G UE-to-Network Relay entity can be used for both public safety services and commercial services (e.g. interactive service). A UE is considered to be a Remote UE for a certain ProSe UE-to- Network relay if it has successfully established a PC5 link to this ProSe 5G UE-to-Network Relay. A Remote UE can be located within NG-RAN coverage or outside of NG-RAN coverage. The ProSe 5G UE-to-Network Relay shall relay unicast traffic (UL and DL) between the Remote UE and the network. The ProSe UE-to-Network Relay shall provide generic function that can relay any IP traffic.

[004] Basic Procedures

[005] A ProSe 5G UE-to-Network Relay capable UE may register to the network (if not already registered) and establish a PDU session enabling the necessary relay traffic, or it may need to connect to additional PDU session(s) or modify the existing PDU session in order to provide relay traffic towards Remote UE(s). PDU session(s) supporting UE-to-Network Relay shall only be used for Remote ProSe UE(s) relay traffic. FIG. 2 is a message flow diagram illustrating steps performed by, among other entities, a ProSe UE-to-NW Relay. The steps shown in FIG. 2 are described below.

0. During the Registration procedure, Authorization and provisioning is performed for the ProSe UE-to-NW relay and Remote UE.

1. The ProSe 5G UE-to-Network Relay may establish a PDU session for relaying with default PDU session parameters received in step 0 or pre-configured in the UE-to-NW relay, e.g. S-NSSAI, DNN, SSC mode. In case of IPv6, the ProSe UE-to-Network Relay obtains the IPv6 prefix via prefix delegation function from the network as defined in TS 23.501.

2. Based on the Authorization and provisioning in step 0, the Remote UE performs discovery of a ProSe 5G UE-to-Network Relay. As part of the discovery procedure the Remote UE learns about the connectivity service the ProSe UE-to-Network Relay provides.

3. The Remote UE selects a ProSe 5G UE-to-Network Relay and establishes a connection for One-to-one ProSe Direct Communication as described in TS 23.287.

If there is no PDU session satisfying the requirements of the PC5 connection with the remote UE, e.g. S-NSSAI, DNN, QoS, the ProSe 5G UE-to-Network Relay initiates a new PDU session establishment or modification procedure for relaying.

4. IPv6 prefix or IPv4 address is allocated for the remote UE as it is defined in

TS 23.303 clauses 5.4.4.2 and 5.4.4.3. From this point the uplink and downlink relaying can start.

5. The ProSe 5G UE-to-Network Relay sends a Remote UE Report (Remote User ID, IP info) message to the SMF for the PDU session associated with the relay. The Remote User ID is an identity of the Remote UE user (provided via User Info) that was successfully connected in step 3. The SMF stores the Remote User IDs and the related IP info in the ProSe 5G UE-to-Network Relay's for the PDU connection associated with the relay. For IP info the following principles apply: a) for IPv4, the UE-to-network Relay shall report TCP/UDP port ranges assigned to individual Remote UE(s) (along with the Remote User ID); b) for IPv6, the UE-to-network Relay shall report IPv6 prefix(es) assigned to individual Remote UE(s) (along with the Remote User ID).

[006] The Remote UE Report message shall be sent when the Remote UE disconnects from the ProSe 5G UE-to-Network Relay (e.g. upon explicit layer-2 link release or based on the absence of keep alive messages over PC5) to inform the SMF that the Remote UE(s) have left.

[007] In the case of Registration Update procedure involving SMF change the Remote

User IDs and related IP info corresponding to the connected Remote UEs are transferred to the new SMF as part of SM context transfer for the ProSe 5G UE-to-Network Relay. In order for the SMF to have the Remote UE(s) information, the HPLMN and the VPLMN where the ProSe 5G UE-to-Network Relay is authorised to operate, needs to support the transfer of the Remote UE related parameters in case the SMF is in the HPLMN. When Remote UE(s) disconnect from the ProSe UE-to-Network Relay, it is up to implementation how relaying PDU sessions are cleared/disconnected by the ProSe 5G UE-to-Network Relay.

[008] After being connected to the ProSe 5G UE-to-Network Relay, the Remote UE keeps performing the measurement of the signal strength of the discovery message sent by the ProSe 5G UE-to-Network Relay for relay reselection.

[009] The solution can also work when the ProSe 5G UE-to-Network Relay UE connects in EPS using LTE. In this case for the Remote UE report the procedures defined in TS 23.303 can be used.

SUMMARY

[0010] Certain challenges presently exist. For example, according to 3GPP TS 22.278, when the ProSe communication is facilitating a UE-to-Network relay, the 3GPP network shall be able to ensure service continuity when the Remote UE changes from a direct 3GPP communication to an Indirect 3GPP Communication and vice-versa, but the solution described above does not address this service continuity issue.

[0011] Accordingly, in one embodiment there is provided a remote UE that is configured to establish a direct connection with a RAN access point, obtain a UE identifier that identifies a relay UE with which the remote UE has a direct connection, and obtain a session identifier that identifies an established session used by the relay UE to relay traffic from the remote UE to a core network function. The remote UE is further configured to transmit, using the direction connection with the RAN access point, a session establishment request. The session establishment request includes: i) the UE identifier that identifies the relay UE, ii) the session identifier that identifies the session used by the relay UE to relay traffic from the remote UE, and iii) a network address that the remote UE received from the relay UE.

[0012] In another aspect there is provided a remote that is configured to initiate the establishment of a direction connection with a relay UE and, after initiating the establishment of the direct connection and before transmitting user plane data to the relay UE, transmit to the relay UE a message. The message includes: i) a UE identifier that identifies the remote UE, ii) a session identifier that identifies a session used by the remote UE to transmit user plane traffic to a core network function, and iii) a network address that has been allocated to the remote UE.

[0013] In another aspect there is provided a relay UE that is configured to receive a request message transmitted by a remote UE with which the relay UE has a direct connection and respond to the request message by transmitting to the remote UE a response message. The response message comprises a temporary ID assigned to the relay UE and further comprises a session ID identifying an established session that is used by the relay UE to relay traffic from the remote UE to a core network function.

[0014] In another aspect there is provided a relay UE that is configured to receive via a direct connection with a remote UE a message transmitted by the remote UE. The message includes a temporary ID assigned to the remote UE and a first session ID identifying a session that is used by the remote UE to transmit user traffic to a core network function. The relay UE is further configured to transmit to a management function a session modification request after receiving the message transmitted by the remote UE. The session modification request includes the temporary ID and the first session ID.

[0015] The embodiments provide the advantage of achieving service continuity when the remote UE changes from a direct 3GPP communication to an indirect 3GPP Communication via a Layer-3 UE-to-Network relay and vice-versa. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate various embodiments.

[0017] FIG. 1 shows the high level view of the non-roaming 5G System (5GS) architecture for vehicle-to-everything (V2X) communication.

[0018] FIG. 2 is a message flow diagram illustrating steps performed by, among other entities, a ProSe UE-to-NW Relay.

[0019] FIG. 3. illustrates a system according to an embodiment.

[0020] FIG. 4 illustrates a protocol stack for the Layer-3 UE-to-Network (UE-NW) Relay according to an embodiment.

[0021] FIG. 5. is a message flow diagram illustrating a message flow according to an embodiment.

[0022] FIG. 6. is a message flow diagram illustrating a message flow according to an embodiment.

[0023] FIG. 7 is a flowchart illustrating a process according to some embodiments.

[0024] FIG. 8 is a flowchart illustrating a process according to some embodiments.

[0025] FIG. 9 is a flowchart illustrating a process according to some embodiments.

[0026] FIG. 10 is a flowchart illustrating a process according to some embodiments.

[0027] FIG. 11 is a flowchart illustrating a process according to some embodiments.

[0028] FIG. 12 is a flowchart illustrating a process according to some embodiments.

[0029] FIG. 13 is a flowchart illustrating a process according to some embodiments.

[0030] FIG. 14 is a flowchart illustrating a process according to some embodiments.

[0031] FIG. 15 illustrates a UE according to some embodiments.

[0032] FIG. 16 illustrates a CN node according to some embodiments. DETAILED DESCRIPTION

[0033] This disclosure provides, among other things, ways to achieve service continuity when a remote UE (e.g., remote ProSe UE) moves from a direct Uu path to an indirect Uu path via a UE-to-Network relay and vice-versa.

[0034] In one embodiment, service continuity is maintained such that when a remote UE moves out of RAN coverage and connects to a Layer-3 (L3) relay UE, the ongoing traffic through its PDU session through the Uu interface should be forwarded to the PDU session that is maintained by the relay UE for remote UEs. Similarly, when the remote UE moves into RAN coverage and can establish its own PDU session, its ongoing traffic through the PDU session that is maintained by the relay UE should be forwarded to its own PDU session.

[0035] In one embodiment, IP address preservation is not required. When the remote UE connects to a Layer-3 UE-to-Network relay, the remote UE gets an IPv6 prefix as described in clause 6.3.3.1 TS 23.287. When the remote UE is in the RAN coverage and can establish its own PDU session, the IPv6 prefix is assigned as described in clause 4.3.2.23GPP TS 23.502 V 16.4.0 (“TS 23.502”).

[0036] In one embodiment, the “make-before-break” principle is followed, meaning that the rmote UE temporarily keeps its current path (a.k.a., the “previous” path) (PC5 or Uu) until the new path has been established, in order to minimize any packet loss and/or packet delay.

[0037] FIG. 3 illustrates a system 300 according to an embodiment. System 300 includes a first UE 301 (referred to herein as the “remote” UE or “UE-1”), a second UE 302 (a.k.a., “UE- 2”), which function as a L3 UE-to-Network (UE-NW) relay, a radio access network (RAN) access point (AP) 304, which in this example is a Next Generation (NG) RAN (NG-RAN) base station (denoted “gNB”), a core network 306, which in this example is a 5G core network (5GC), an application server (AS) 308. As shown in FIG. 3, 5GC includes at a first Access and Mobility Management Function (AMF) (a.k.a., AMF-1), a second AMF (a.k.a., AMF-2), a first Session Management Function (SMF) (a.k.a., SMF-1), a second SMF (a.k.a., SMF-2), a first User Plane Function (UPF) (a.k.a., UPF-1), a second UPF (a.k.a., UPF-2), and a Branching Point (BP) UPF. FIG. 4 shows the protocol stack for remote UE 301 and UE-NW relay 302. [0038] AMF-1 and SMF-1 serve UE-1 when UE-1 has a direct connection with AP 304

(i.e., UE-1 has a direct Uu path with AP 304). AMF-2 and SMF-2 serve UE-2, and it is assumed that UE-2 always has a direct connection with an AP. UPF-1 is the UPF PDU session anchor (PSA) for UE-1 PDU session of its direct connection. UPF-2 is the UPF PSA for the UE-2 PDU session which is used for transferring traffic of UE- 1 when it connects to UE-2 for an indirect AP connection. AMF-1 and AMF-2 may be the same AMF. Likewise, SMF-1 and SMF-2 may be the same SMF, and UPF-1 and UPF-2 may be the same UPF.

[0039] FIG. 5 is a message flow diagram illustrating service continuity for path switching from an indirect Uu path via UE-2 (relay UE) to a direct Uu path. The steps shown in FIG. 5 are described below.

[0040] Step 0. UE-1 (remote UE) accesses the network via UE-2. UE-l’s traffic is going through a PDU session of UE-2. That is, when UE-2 transmits application layer protocol data units (PDUs), which are encapsulated in Internet Protocol (IP) packets, the PDUs are received at UE-2 and forwarded by UE-2 to a UPF in the 5GC 306 via AP 304 (gNB in this example).

[0041] Step 1. UE-1 moves into coverage of a gNB and can have a direct Uu path to the gNB. In this step, the UE-1 may establish a Radio Resource Control (RRC) connection with the gNB and initiate the registration procedure with 5GC.

[0042] Step 2. UE-1 gets UE-2’s Globally Unique Temporary Identity (GUTI) and the

PDU session ID for UE-2’s PDU session, which UE-l’s traffic is going through. Step 2 can happen before step 1. For example, step 2 comprises UE- 1 transmitting a request message to UE-2 and UE-2 responding to the request by transmitting a response message comprising UE-2’s GUTI and the PDU session ID.

[0043] Step 3. The UE-1 starts to establish a PDU session via the direct Uu path. That is,

UE- 1 transmits a PDU session establishment request, which is received by the gNB and forwarded to an AMF (e.g., AMF-1). In the PDU session establishment request, the UE-1 includes extra parameters such as, UE-2’s GUTI, UE-2’s PDU session ID, UE-1 ’s old IPv6 Prefix which was provided to UE- 1 by UE-2. Accordingly, the PDU session establishment request may include not only a new PDU session ID generated to UE-1 and a Request Type value (e.g., “initial request”), but also the extra parameters mentioned above. [0044] Step 4 (optional). Steps 4 and 5 are performed if UE-1 and UE-2 are served by different AMFs (i.e., AMF-1 not the same AMF as AMF-2), otherwise steps 4 and 5 are not necessary. AMF-1 sends the UE context request to AMF-2 to get the Subscription Permanent Identifier (SUPI) of UE-2 as well as the ID of the SMF who is serving UE-2 (i.e., SMF-2 ID).

[0045] Step 5 (optional). AMF-2 gives AMF-1 the SUPI of UE-2 and the SMF-2 ID.

[0046] Step 6. AMF-1 sends an Nsmf_PDUSession_CreateSMContext request to SMF-1 with the extra parameters: UE-2’s SUPI, SMF-2 ID (if SMF-2 if different from SMF-1), PDU session ID of UE-2’s PDU session, UE-l’s old IPv6 prefix. Accordingly, the Nsmf_PDUSession_CreateSMContext request may include not only UE-1 ’s SUPI, UE-1 ’s PDU session ID, and Request Type, but also the extra parameters mentioned above.

[0047] Step 7. SMF-1 initiates an N4 Session Establishment procedure as described in steps 8-10 in clause 4.3.2.2.1 TS 23.502. For example, in step 7, SMF-1 selects a UPF (e.g., UPF-1) and transmits to the selected UPF an N4 Session Establishment Request or an N4 Session Modification Request.

[0048] Step 8. SMF-1 selects a BP UPF and configures the BP UPF via the N4 interface.

It provides the BP UPF with the necessary UF traffic forwarding rules (related with the prefix of the IPv6 source address anchored in UPF-1). Also, SMF-1 provides core network (CN) tunnel information for an N9 tunnel setup to the BP UPF and obtains CN tunnel information from the BP UPF.

[0049] Step 9. SMF-1 performs N4 Session Modification procedure with UPF-1. During this procedure, SMF-1 provides the CN Tunnel Info received from the BP UPF to set up an N9 tunnel between BP UPF and UPF-1.

[0050] Step 10 (optional). This step is performed when SMF-1 and SMF-2 are different

SMFs. SMF-1 invokes Nsmf_PDUsession_Update request to SMF-2 with the extra parameters, such as UE-2’s SUPI, UE-2’s PDU session ID, DF traffic forwarding rules (related with the old IPv6 prefix of UE-1 which is anchored in UPF-2), CN Tunnel Info from the BP UPF.

[0051] Step 11. If SMF-1 and SMF-2 are not the same SMF, then SMF-2 performs N4

Session Modification procedure with UPF-2, otherwise SMF-1 performs the N2 Session Modification Procedure with UPF-2. During this procedure, SMF-l/SMF-2 provides CN Tunnel Info of the BP UPF to set up an N9 tunnel between BP UPF and UPF-2.

[0052] Step 12 (optional). This step is performed when SMF-1 and SMF-2 are different

SMFs. SMF-2 sends back the Nsmf_PDUsession_Update response with the extra parameters, such as CN Tunnel Info for N9 tunnel with UPF-2.

[0053] Step 13. SMF-1 provides the BP UPF with the necessary UL traffic forwarding rules (related with the old IPv6 prefix of UE-1 which is anchored in UPF-2). Also, the SMF-1 provides CN Tunnel Info for N9 tunnel got from UPF-2 (via SMF-2) to setup an N9 tunnel between BP and UPF-2.

[0054] Step 14. RAN handling and RRC reconfiguration

[0055] Step 15. SMF-1 provides AN Tunnel Info to the BP UPF as well as the DL traffic forwarding rules.

[0056] At this point, the traffic with the old and new IPv6 prefixes of UE- 1 can be forwarded to/from the corresponding anchor UPFs via the BP UPF.

[0057] Step 16. After a timeout, SMF-2 removes the DF traffic forwarding rule for the old IPv6 prefix of UE- 1 , so that UE-2 can allocate that prefix to some other remote UEs connected to it. SMF-1 removes the corresponding UF traffic forwarding rule in the BP UPF and releases the N9 tunnel between the BP UPF and UPF-2.

[0058] SMF-1 may optionally release the BP UPF from the User Plane path as describe in step 14-18 in clause 4.3.5.3 TS 23.502.

[0059] FIG. 6 is a message flow diagram illustrating service continuity for path switching from a direct Uu path to an indirect Uu path via UE-2. The steps shown in FIG. 6 are described below.

[0060] Step 0. UE-1 and UE-2 both have Uu connections and can send and receive traffic via their own PDU sessions.

[0061] Step 1. UE-1 moves out of the network coverage and initiates the relay selection and path establishment with the selected relay as described in 3GPP TR 23.752 V0.3.0 solution #6 - - i.e., UE-1 gets a new IPv6 prefix from UE-2 and can send and receive traffic using the new IPv6 prefix via UE-2’s PDU session.

[0062] Step 2. UE-1 gives its GUTI, PDU session ID, and its old IPv6 prefix to UE-2, indicating that it wants to move its traffic with the old IPv6 prefix to the new path. Step 2 may be performed by UE- 1 during the procedure of establishing the direct connection with UE-2 (e.g., as part of step 4 shown in FIG. 2).

[0063] Step 3. The UE-2 starts to modify its PDU session. That is, UE-2 transmits to its serving AMF (i.e., AMF-2) a PDU session modification request. In the PDU session modification request, UE-2 includes extra parameters such as, UE-l’s GUTI, UE-l’s PDU session ID, UE-1 ’s old IPv6 Prefix, which UE-2 obtained in step 2. Accordingly, the PDU session modification request may include not only PDU session ID identifying UE-2’s PDU session to be modified, but also the extra parameters mentioned above.

[0064] Step4 (optional). Steps 4 and 5 are performed if UE-1 and UE-2 are served by different AMFs, otherwise steps 4 and 5 are not necessary. AMF-2 sends the UE context request to AMF-1 to get the SUPI of UE-1 as well as the ID of the SMF who is serving UE-1 (i.e. SMF- 1 ID).

[0065] Step 5 (optional). AMF-1 gives AMF-2 the SUPI of UE-1 and the SMF-1 ID.

[0066] Step 6. AMF-2 sends an Nsmf_PDUSession_UpdateSMContext request to SMF-2 with the extra parameters: UE-1 ’s SUPI, SMF-1 ID (if SMF-1 is different from SMF-2), UE-1 ’s old IPv6 prefix. Accordingly, the Nsmf_PDUSession_CreateSMContext request may include not only UE-2’s SUPI, and UE-2’s PDU session ID, but also the extra parameters mentioned above.

[0067] Step 7. SMF-2 selects a BP UPF and configures the selected BP UPF via N4. It provides the BP UPF with the necessary UL traffic forwarding rules (related with the prefix of the IPv6 source address anchored in UPF-2). Also, the SMF-2 provides AN Tunnel Info for N3 tunnel setup and CN Tunnel Info for N9 tunnel setup to the BP UPF and obtains CN Tunnel Info from the BP UPF. [0068] Step 8. SMF-2 performs N4 Session Modification procedure with UPF-2. During this procedure, SMF-2 provides CN Tunnel Info received from the BP UPF to set up an N9 tunnel between BP and UPF-2.

[0069] Step 9 (optional). Step 9 is performed when SMF-1 and SMF-2 are different

SMFs. SMF-2 invokes Nsmf_PDUsession_Update request to SMF-1 with the extra parameters, such as UE-1 ’s SUPI, UE-1 ’s PDU session ID, DL traffic forwarding rules (related with the old IPv6 prefix of UE-1 which is anchored in UPF-1), CN Tunnel Info from the BP UPF.

[0070] SteplO. If SMF-1 is not the same as SMF-2, then SMF-1 performs N4 Session

Modification procedure with UPF-1, otherwise SMF-2 performs the N4 Session Modification procedure with UPF-1. During this procedure, SMF-l/SMF-2 provides CN Tunnel Info of the BP UPF to set up an N9 tunnel between BP UPF and UPF-1.

[0071] Step 11 (optional). This step is performed when SMF-1 and SMF-2 are different

SMFs. SMF-1 sends back the Nsmf_PDUsession_Update response with the extra parameters, such as CN Tunnel Info for N9 tunnel with UPF-1.

[0072] Step 12. SMF-2 provides the BP UPF with the necessary UF traffic forwarding rules (related with the old IPv6 prefix of UE-1 which is anchored in UPF-1). Also, SMF-2 provides CN Tunnel Info for N9 tunnel got from UPF-1 (via SMF-1) to setup an N9 tunnel between BP and UPF-1.

[0073] Step 13. SMF interacts with NG-RAN and the UE corresponding to the PDU session modification, including providing to RAN the CN Tunnel Info for the N3 tunnel setup with BP UPF. Details are omitted here. After step 13, UE-2 maintains a routing rule mapping UE-1 and its old IPv6 prefix, and UE-2 also informs UE-1 that it can send the traffic belongs to the old PDU session through the new path now.

[0074] At this point the traffic with the old and new IPv6 prefixes of UE- 1 can be forwarded to/from the corresponding anchor UPF via the BP UPF and UE-2.

[0075] Step 14. After a timeout, SMF-1 removes the DF traffic forwarding rule for the old IPv6 prefix of UE-1. SMF-2 removes the corresponding UF traffic forwarding rule in the BP UPF and releases the N9 tunnel between the BP UPF and UPF-1. SMF-2 may optionally release the BP UPF from the User Plane path as describe in step 14-18 in clause 4.3.5.3 TS 23.502.

[0076] FIG. 15 is a block diagram of a UE 1500 (e.g., UE-1 or UE-2), according to some embodiments. As shown in FIG. 15, UE 1500 may comprise: processing circuitry (PC) 1502, which may include one or more processors (P) 1555 (e.g., one or more general purpose microprocessors and/or one or more other processors, such as an application specific integrated circuit (ASIC), field-programmable gate arrays (FPGAs), and the like); communication circuitry 1548, which is coupled to an antenna arrangement 1549 comprising one or more antennas and which comprises a transmitter (Tx) 1545 and a receiver (Rx) 1547 for enabling UE 1500 to transmit data and receive data (e.g., wirelessly transmit/receive data); and a local storage unit (a.k.a., “data storage system”) 1508, which may include one or more non-volatile storage devices and/or one or more volatile storage devices. In embodiments where PC 1502 includes a programmable processor, a computer program product (CPP) 1541 may be provided. CPP 1541 includes a computer readable medium (CRM) 1542 storing a computer program (CP) 1543 comprising computer readable instructions (CRI) 1544. CRM 1542 may be a non-transitory computer readable medium, such as, magnetic media (e.g., a hard disk), optical media, memory devices (e.g., random access memory, flash memory), and the like. In some embodiments, the CRI 1544 of computer program 1543 is configured such that when executed by PC 1502, the CRI causes UE 1500 to perform steps described herein (e.g., steps described herein with reference to the flow charts). In other embodiments, UE 1500 may be configured to perform steps described herein without the need for code. That is, for example, PC 1502 may consist merely of one or more ASICs. Hence, the features of the embodiments described herein may be implemented in hardware and/or software

[0077] FIG. 16 is a block diagram of an core network (CN) node 1600, according to some embodiments, for implementing any one of the CN functions (e.g., AMF, SMF, UPF, etc.). As shown in FIG. 16, CN node 1600 may comprise: processing circuitry (PC) 1602, which may include one or more processors (P) 1655 (e.g., a general purpose microprocessor and/or one or more other processors, such as an application specific integrated circuit (ASIC), field- programmable gate arrays (FPGAs), and the like), which processors may be co-located in a single housing or in a single data center or may be geographically distributed (i.e., CN node 1600 may be a distributed computing apparatus); at least one network interface 1648 comprising a transmitter (Tx) 1645 and a receiver (Rx) 1647 for enabling CN node 1600 to transmit data to and receive data from other nodes connected to a network 110 (e.g., an Internet Protocol (IP) network) to which network interface 1648 is connected (directly or indirectly) (e.g., network interface 1648 may be wirelessly connected to the network 110, in which case network interface 1648 is connected to an antenna arrangement); and a storage unit (a.k.a., “data storage system”) 1608, which may include one or more non-volatile storage devices and/or one or more volatile storage devices. In embodiments where PC 1602 includes a programmable processor, a computer program product (CPP) 1641 may be provided. CPP 1641 includes a computer readable medium (CRM) 1642 storing a computer program (CP) 1643 comprising computer readable instructions (CRI) 1644. CRM 1642 may be a non-transitory computer readable medium, such as, magnetic media (e.g., a hard disk), optical media, memory devices (e.g., random access memory, flash memory), and the like. In some embodiments, the CRI 1644 of computer program 1643 is configured such that when executed by PC 1602, the CRI causes CN node 1600 to perform steps described herein (e.g., steps described herein with reference to the flow charts). In other embodiments, CN node 1600 may be configured to perform steps described herein without the need for code. That is, for example, PC 1602 may consist merely of one or more ASICs. Hence, the features of the embodiments described herein may be implemented in hardware and/or software.

[0078] Summary of Various Embodiments

[0079] Remote UE

[0080] Al. A method 700 (see FIG. 7) performed by a remote UE (301) that has a direct connection with a relay UE (302), the method comprising: the remote UE establishing (s702) a direct connection with a radio access network, RAN, access point; the remote UE obtaining (s704) a UE identifier that identifies the relay UE (e.g., the relay UE’s GUTI) and a session identifier that identifies an established session used by the relay UE to relay traffic from the remote UE to a core network function; and the remote UE transmitting (s706), using the direction connection with the RAN access point, a session establishment request, wherein the session establishment request comprises: i) the UE identifier that identifies the relay UE, ii) the session identifier that identifies the session used by the relay UE to relay traffic from the remote UE, and iii) a network address (e.g. IPv6 Prefix) that the remote UE received from the relay UE.

[0081] A2. The method of embodiment Al, wherein the session establishment request comprises a new session ID generated by the remote UE and a request type indicating the session establishment request is an initial request.

[0082] Remote UE

[0083] Bl. A method 800 (see FIG. 8) performed by a remote UE (301) that has a direct connection with a radio access network, RAN, access point (e.g., a gNB), the method comprising: the remote UE initiating (s802) the establishment of a direction connection with a relay UE (302); after initiating the establishment of the direct connection and before transmitting user plane data to the relay UE, the remote UE transmitting (s804) to the relay UE a message comprising: i) a UE identifier that identifies the remote UE (e.g., the remote UE’s GUTI), ii) a session identifier that identifies a session used by the remote UE to transmit user plane traffic to a core network function, and iii) a network address (e.g. IPv6 Prefix) that has been allocated to the remote UE.

[0084] B2. The method of embodiment B 1, wherein the message triggers the relay UE to transmit a PDU session modification request that comprises: i) the UE identifier, ii) the session identifier, and iii) the network address.

[0085] Rely UE

[0086] C 1. A method 900 (see FIG. 9) performed by a relay UE (302) that has a direct connection with a remote UE (301), the method comprising: the relay UE receiving (s902) a request message transmitted by the remote UE; and the relay UE responding (s904) to the request message by transmitting to the remote UE a response message that comprises a temporary identifier, ID, assigned to the relay UE (e.g. GUTI) and further comprises a session ID identifying an established session that is used by the relay UE to relay traffic from the remote UE to a core network function.

[0087] C2. The method of embodiment C 1 , wherein the established session is an established PDU session. [0088] Relay UE

[0089] Dl. A method 1000 (see FIG. 10) performed by a relay UE (302) that has a direct connection with a remote UE (301), the method comprising: the relay UE receiving (sl002) via the direct connection with the remote UE a message transmitted by the remote UE, the message comprising: a temporary identifier, ID, assigned to the remote UE (e.g. GUTI) and a first session ID identifying a session that is used by the remote UE to transmit user traffic to a core network function; and after receiving the message, the relay UE transmitting (sl004) to a management function (e.g., AMF-2) a session modification request, the session modification request comprising the temporary ID and the first session ID received from the remote UE.

[0090] D2. The method of embodiment D 1 , wherein the session modification request further comprises: a second session ID identifying an established session used by the relay UE.

[0091] AMF-1

[0092] El. A method 1100 (see FIG. 11) performed by a first management function (e.g.,

AMF-1), the method comprising: the first management function receiving (si 102) a session establishment request transmitted by a remote UE, the session establishment request comprising: a temporary identifier, ID, assigned to a relay UE that was or is providing a relay service to the remote UE and a session ID identifying a session used by the relay UE to relay traffic from the remote UE; and after receiving the session establishment request, the first management function transmitting (si 104) to a first session management function (e.g., SMF-1) a session management request message (e.g., Nsmf_PDUSession_CreateSMContext) comprising the session ID.

[0093] E2. The method of embodiment El, wherein the session establishment request further comprising a network address (e.g., IPv6 prefix) allocated to the remote UE.

[0094] E3. The method of embodiment El or E2, further comprising: after receiving the session establishment request, the first management function transmitting to a second management function a request for context information for the relay UE, the request for context information comprising the temporary ID assigned to the relay UE; and the first management function receiving a responsive message transmitted by the second management function in response to the request for the context information, the responsive message comprising a subscription identity for the relay UE and a session management function ID identifying the first session management function or a second management function.

[0095] E4. The method of any one of embodiments E1-E3, wherein the session management request message further comprises the subscription identity for the relay UE.

[0096] AMF-2

[0097] FI. A method 1200 (see FIG. 12) performed by a first management function (e.g.,

AMF-2), the method comprising: the first management function receiving (sl202) a session modification request transmitted by a relay UE that has a direct connection with a remote UE, the session modification request comprising: i) a temporary identifier, ID, assigned to the remote UE and ii) a session ID identifying a session that is used by the remote UE to transmit user traffic to a core network function; and after receiving the session modification request, the first management function transmitting (sl204) a message (e.g.,

Nsmf_PDUSession_UpdateSMContext message) to a session management function, wherein the message comprises the session ID.

[0098] F2. The method of embodiment FI, further comprising using the temporary ID to obtain a subscription identity (e.g., SUPI) associated with the temporary ID, wherein the message further comprises the subscription identity.

[0099] F3. The method of embodiment F2, wherein using the temporary ID to obtain the subscription identity comprises: the first management function transmitting to a second management function a request message comprising the temporary ID and receiving a responsive message responding to the request message wherein the responsive message comprises the subscription identity.

[00100] F4. The method of embodiment F3, wherein the responsive message further comprises an SMF ID identifying an SMF serving the remote UE.

[00101] SMF- 1

[00102] Gl. A method 1300 (see FIG. 13) performed by a first session management function, SMF(e.g., SMF-1), the method comprising: the first SMF receiving (si 302) a session management request message (e.g., Nsmf_PDUSession_CreateSMContext) transmitted by a first management function (e.g., AMF-1) that is serving a remote UE, the session management request message comprising: i) a first session identifier (e.g., a first PDU session identifier) identifying a session used by a relay UE to relay traffic from the remote UE and ii) a network address (e.g., IPv6 prefix) allocated to the remote UE; and after receiving the session management request message, the fist SMF transmitting (si 304) to a UPF a session request message (e.g., N4 Session Establishment Request or an N4 Session Modification Request).

[00103] G2. The method of embodiment Gl, wherein the session management request further comprises a second session ID that was generated by the remote UE.

[00104] G3. The method of embodiment G2, wherein the session management request further comprises a subscription identity for the remote UE.

[00105] G4. The method of any one of embodiments G1-G3, wherein the session management request message (e.g., Nsmf_PDUSession_CreateSMContext) further comprises: a subscription identity of the relay UE and an SMF ID identifying an SMF (e.g., SMF-2) serving the relay UE.

[00106] SMF-2

[00107] HI. A method 1400 (see FIG. 14) performed by a first session management function, SMF (e.g., SMF-2), the method comprising: the first SMF receiving (sl402) a session management request message (e.g., Nsmf_PDUSession_UpdateSMContext) transmitted by a first management function (e.g., AMF-2) that is serving a relay UE that has a direct connection with a remote UE, the session management request message comprising: i) a first session identifier (e.g., PDU session identifier) identifying an established session used by the remote UE and ii) a second session identifier identifying an established session used by the relay UE; and after receiving the session management request message, the first SMF transmitting (si 404) to a UPF a first session request message (e.g., N4 Session Establishment Request or an N4 Session Modification Request).

[00108] H2. The method of embodiment HI, wherein the session management request message further comprises a subscription identity for the remote UE. [00109] H3. The method of embodiment HI or H2, wherein the session management request message further comprises an SMF ID identifying a second SMF (e.g., SMF-1) that is serving the remote UE.

[00110] H4. The method of embodiment H3, further comprising the first SMF transmitting to the second SMF a request message comprising a subscription identity for the remote UE, a session ID identifying an established session used by the remote UE, a DL traffic forwarding rule, CN tunnel information obtained from a BP UPF.

[00111] H5. The method of any one of embodiments H1-H4, wherein the session management request message (e.g., Nsmf_PDUSession_UpdateSMContext) further comprises: a subscription identity of the remote UE and an SMF ID identifying an SMF (e.g., SMF-1) serving the remote UE.

[00112] II. A computer program (1543) comprising instructions (1544) which when executed by processing circuitry (1502) of a UE (1500) causes the UE (1500) to perform the method of any one of embodiments A1-D2.

[00113] 12. A computer program (1643) comprising instructions (1644) which when executed by processing circuitry (1602) of a CN node (1600) causes the CN node (1600) to perform the method of any one of embodiments E1-H5.

[00114] 13. A carrier containing the computer program of embodiment II or 12, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a computer readable storage medium (1542, 6742).

[00115] FI. A UE (1500), the UE (1500) being adapted to perform the method of any one of embodiments A1-D2.

[00116] Gl. A UE (1500), the UE (1500) comprising: processing circuitry (1502); and a memory (1542), the memory containing instructions (1544) executable by the processing circuitry, whereby the RAN node is operative to perform the method of any one of the embodiments A1-D2.

[00117] HI. A CN node (1600), the CN node (1600) being adapted to perform the method of any one of embodiments E1-H5. [00118] II. A CN node (1600), the CN node (1600) comprising: processing circuitry (1602); and a memory (1642), the memory containing instructions (1644) executable by the processing circuitry, whereby the CN node is operative to perform the method of any one of the embodiments E1-H5.

[00119] While various embodiments are described herein, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of this disclosure should not be limited by any of the above -described exemplary embodiments. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

[00120] Additionally, while the processes described above and illustrated in the drawings are shown as a sequence of steps, this was done solely for the sake of illustration. Accordingly, it is contemplated that some steps may be added, some steps may be omitted, the order of the steps may be re-arranged, and some steps may be performed in parallel.

[00121] References:

[00122] [1] 3GPP TS 23.303 V15.10.0, Proximity-based services (ProSe).

[00123] [2] 3GPP TS 23.287 Architecture enhancements for 5G System (5GS) to support Vehicle-to-Everything (V2X) services.

[00124] [3] 3GPP TR 23.752, Study on system enhancement for Proximity based

Services (ProSe) in the 5G System (5GS).

[00125] [4] 3GPP TS 23.501, System architecture for the 5G System (5GS).

[00126] [5] 3GPP TS 23.502, Procedures for the 5G System (5GS).

Claims

1. A remote UE (301), the remote UE being configured to: establish a direct connection with a radio access network, RAN, access point (304); obtain a UE identifier that identifies a relay UE (302) with which the remote UE has a direct connection, obtain a session identifier that identifies an established session used by the relay UE to relay traffic from the remote UE to a core network function; and transmit, using the direction connection with the RAN access point, a session establishment request, wherein the session establishment request comprises: i) the UE identifier that identifies the relay UE, ii) the session identifier that identifies the session used by the relay UE to relay traffic from the remote UE, and iii) a network address that the remote UE received from the relay UE.

2. The remote UE of claim 1 , wherein the session establishment request comprises a new session ID generated by the remote UE and a request type indicating the session establishment request is an initial request.

3. The remote UE of claim 1 or 2, wherein the UE identifier that identifies the relay UE is a Globally Unique Temporary Identity, GUTI, assigned to the relay UE.

4. The remote UE of claim 1, 2, or 3, wherein the network address is an IPv6 prefix.

5. A remote UE (301), the remote UE being configured to: initiate the establishment of a direction connection with a relay UE (302); after initiating the establishment of the direct connection and before transmitting user plane data to the relay UE, transmit to the relay UE a message comprising: i) a UE identifier that identifies the remote UE, ii) a session identifier that identifies a session used by the remote UE to transmit user plane traffic to a core network function, and iii) a network address that has been allocated to the remote UE.

6. The remote UE of claim 5, wherein the message triggers the relay UE to transmit a protocol data unit, PDU, session modification request that comprises: i) the UE identifier, ii) the session identifier, and iii) the network address.

7. A relay UE (302), the relay UE being configured to: receive a request message transmitted by a remote UE (301) with which the relay UE has a direct connection; and respond to the request message by transmitting to the remote UE a response message that comprises a temporary identifier, ID, assigned to the relay UE and further comprises a session ID identifying an established session that is used by the relay UE to relay traffic from the remote UE to a core network function.

8. The relay UE of claim 7, wherein the established session is an established protocol data unit, PDU, session.

9. A relay UE (302), the relay UE being configured to: receive via a direct connection with a remote UE (301) a message transmitted by the remote UE, the message comprising: a temporary identifier, ID, assigned to the remote UE and a first session ID identifying a session that is used by the remote UE to transmit user traffic to a core network function; and after receiving the message, transmit to a management function (AMF-2) a session modification request, the session modification request comprising the temporary ID and the first session ID.

10. The relay UE of claim 9, wherein the session modification request further comprises: a second session ID identifying an established session used by the relay UE.

11. The relay UE of claim 9 or 10, wherein the session modification request is a protocol data unit, PDU, session modification request.

12. The relay UE of claim 9, 10, or 11, wherein the management function is an Access and Mobility Management Function, AMF.