U2U relay communication

Abstract

A method comprises: for a U2U relay communication between UE1 and UE2: determining a first local identifier (LID) such that the first LID is unique among all LIDs associated with an identifier of a first hop in a mapping table; storing, in a mapping table, first mapping information mapped to the U2U relay communication ID, wherein the first mapping information comprises an identifier of a first hop associated with the first LID; and-indicating to establish a portion of a connection for U2U relay communication via the first hop, wherein the indication comprises the first LID; supervising whether the UE1 intends to send data of the U2U relay communication to the UE2; identifying, based on the U2U relay communication ID, identified mapping information, the identified mapping information comprising an identifier of an egress hop associated with the identified LID, where the identified mapping information is mapped to the U2U relay communication ID in a mapping table; and transmitting data including the identified LID on the egress hop.

Description

Technical Field

[0001] The present disclosure relates to U2U relay communications (eg, on a sidelink).

[0002] abbreviation

[0003] 3GPP: Third Generation Partnership Project

[0004] 5G / 6G / 7G: fifth generation / sixth generation / seventh generation

[0005] CP: Control Plane

[0006] C-RNTI: Cell RNTI

[0007] DCA: Direct Communication Acceptance

[0008] DCR: Direct Communication Request

[0009] DST: Destination

[0010] E2E: End to End

[0011] gNB: Next Generation NodeB

[0012] HARQ: Hybrid Automatic Repeat Request

[0013] ID: Identifier

[0014] IP: Internet Protocol

[0015] L2: Layer 2 (usually includes MAC sublayer, RLC sublayer and / or PDCP sublayer)

[0016] LID: Local ID

[0017] MAC: Media Access Control

[0018] NR: New Radio

[0019] PDCP: Packet Data Convergence Protocol

[0020] PHY: Physical layer (= Layer 1)

[0021] ProSe: Proximity Services

[0022] QoS: Quality of Service

[0023] RD: Relay Discovery

[0024] RLC: Radio Link Control

[0025] RNTI: Radio Network Temporary Identifier

[0026] RRC: Radio Resource Control

[0027] SD: Sidelink Discovery

[0028] SDAP: Service Data Application Protocol

[0029] SL: Sidelink

[0030] SRAP: Sidelink Relay Adaptation Protocol

[0031] src: source

[0032] TMSI: Temporary Mobile Subscriber Identity

[0033] TR: Technical Report

[0034] TS: Technical Specification

[0035] U2N: UE to Network

[0036] U2U: UE to UE

[0037] UE: User Equipment

[0038] UP: User Plane

[0039] V2X: Vehicle to Everything Background Art

[0040] The objectives for 3GPP Rel-18 Sidelink (SL) UE-to-UE (U2U) relay are described in 3GPP RP-221262 as follows:

[0041] The goal of this work item is to specify the solutions needed to enhance NR sidelink relay for V2X, public safety and commercial use cases.

[0042] 1. Specify mechanisms to support single-hop Layer 2 and Layer 3 UE-to-UE relay (ie, source UE->relay UE->destination UE) for unicast [RAN2, RAN3, RAN4].

[0043] A. Common parts for layer 2 and layer 3 trunking will be given priority until RAN#98

[0044] i. Relay discovery and (re)selection [RAN2, RAN4]

[0045] ii. If SA2 concludes that relay and remote UE authorization is required, provide signaling support for relay and remote UE authorization [RAN3]

[0046] B. Layer 2 relay specific parts

[0047] i. UE-to-UE relay adaptation layer design [RAN2]

[0048] ii. Control Plane Procedures [RAN2]

[0049] iii. QoS treatment (if required), subject to SA2 progress [RAN2]

[0050] NOTE 1A: This work should be considered for forward compatibility to support more than one hop in future releases.

[0051] NOTE 1B: For a given destination UE, a remote UE is only connected to a single relay UE at a given time.

[0052] 3GPP TR 38.836 captures the results of studies on SL relaying including U2U relaying. It has been agreed that L2 U2U relaying requires the following adaptation layer, copied from 3GPP TR 38.836:

[0053] 5.5.1 Architecture and Protocol Stack

[0054] For L2 UE to UE relay architecture, the protocol stack is similar to L2 UE to network relay, except for the fact that the termination points are two remote UEs. The protocol stack for the user plane and control plane for L2 UE to UE relay architecture is described in Figure 5 .5.1-1 and Figure 5 .Described in 5.1-2.

[0055] An adaptation layer is supported on the second PC5 link (i.e., the PC5 link between the relay UE and the destination UE) for L2UE-to-UE relay. For L2 UE-to-UE relay, an adaptation layer is placed on the RLC sublayer for both CP and UP on the second PC5 link. Sidelink SDAP / PDCP and RRC are terminated between the two remote UEs, while RLC, MAC, and PHY are terminated in each PC5 link.

[0056] For the first hop of L2 UE to UE relay:

[0057] - N:1 mapping is supported by the first hop PCV adaptation layer between the remote UE SL radio bearer and the first hop PC5 RLC channel for relaying.

[0058] - The adaptation layer on the first PC5 hop between the source remote UE and the relay UE supports identifying traffic destined for different destination remote UEs.

[0059] For the second hop of L2 UE to UE relay:

[0060] - The second hop PC5 adaptation layer may be used to support bearer mapping between an ingress RLC channel on the first PC5 hop and an egress RLC channel on the second PC5 hop at the relay UE.

[0061] - The PC5 adaptation layer supports N:1 bearer mapping between multiple ingress PC5 RLC channels on the first PC5 hop and one egress PC5 RLC channel on the second PC5 hop, and supports remote UE identification functionality.

[0062] For L2 UE to UE relay:

[0063] - Identity information of the remote UE end-to-end radio bearers is included in the adaptation layer in the first PC5 hop and the second PC5 hop.

[0064] - In addition, the identity information of the source remote UE and / or the identity information of the destination remote UE are candidate information to be included in the adaptation layer, which will be decided in the WI stage.

[0065] Figure 1 shows a user plane protocol stack for L2 UE-to-UE relay, and Figure 2 The control plane protocol stack for L2 UE-to-UE relay is shown. The adaptation layer is shown directly above the RLC layer and below the PDCP layer.

[0066] 3GPP TS 38.351 specifies the SL Relay Adaptation Protocol (SRAP) for L2 U2N relay. Figure 3 (copied from 3GPP TS 38.351) shows how to use the 8-bit UE ID to indicate the local ID of the remote UE in the SRAP PDU header:

[0067] According to 3GPP TS23.303 clause 5.3.1.2, there are the following Model A and Model B for ProSe direct discovery:

[0068] Model A (“I am here”)

[0069] This model defines two roles for a ProSe-enabled UE participating in ProSe direct discovery.

[0070] - Announcing UE: This UE announces certain information which can be used by nearby UEs that have the right to discover it.

[0071] - Monitoring UE: A UE that monitors certain information of interest in the vicinity of announcing UE.

[0072] In this model, announcing UEs broadcast discovery messages at predefined discovery intervals, and monitoring UEs interested in these messages read the discovery messages and process them.

[0073] Model A is equivalent to “I am here” because the announcing UE will broadcast information about itself in the discovery message, such as the ProSe application code of the announcing UE.

[0074] Model B (“Who’s there?” / “Are you there?”)

[0075] This model defines two roles for a ProSe-enabled UE participating in ProSe direct discovery.

[0076] - Discoverer UE: This UE sends a request containing some information about what this UE is interested in discovering.

[0077] - Discoverer UE: The UE that receives the request message, which can respond with some information related to the discoverer's request.

[0078] Model B is equivalent to “Who’s there / Are you there” in that the discoverer UE sends information about other UEs from which it hopes to receive responses, for example, the information may be information about the ProSe application identity corresponding to the group, and members of the group may respond.

[0079] 3GPP TR 23.700-33 proposes a number of advanced solutions to support SL U2U relay. In Section 6.1 of 3GPP TR 23.700-33, it is recommended to integrate the discovery of DST UE and the discovery and selection of SL U2U relay UE. 3GPP TR 23.700-33 discloses two alternative solutions:

[0080] - Alternative 1 (such as Figure 4 ): UE-to-UE relay discovery and selection can be integrated into the unicast link creation process as described in 3GPP TS23.304 section 6.4.3.1.

[0081] - Alternative 2 (such as Figure 5 ): UE-to-UE relay discovery and selection are integrated into the Model B direct discovery process.

[0082] Basically, under Option 1 ( Figure 4 ), UE-1 (SRC UE) broadcasts DCR for direct communication with UE-2 (DST UE) to indicate that relaying is permitted. UE-2 may not receive DCR because it is far away from UE-1 (e.g. Figure 4), but UE Relay 1 and UE Relay 2 are near both UE-1 and UE-2, receive the DCR broadcast from UE-1, and decide to participate in the relay. Therefore, the UE Relay 1 and the UE Relay 2 broadcast another DCR received by UE-2. UE-2 decides which relay UE will accept (here: UE Relay 1 is selected). After creating the security context, UE-2 sends a DCA to the selected relay UE (UE Relay 1), and the relay UE forwards the same DCA to UE-1. Therefore, by creating direct communications between UE-1 and UE Relay 1 and between UE Relay 1 and UE-2 and relaying these direct communications at UE Relay 1, a connection for U2U communication between UE-1 and UE-2 is created. According to Alternative Scheme 1, the selection of relay UEs participating in the connection is performed in the direction from the DSTUE to the SRC UE.

[0083] According to Alternative 2 ( Figure 5 ), UE-1 (SRC UE) broadcasts a discovery solicitation to indicate that it wants to establish a connection with UE-2 for U2U communication. UE-R receives the discovery solicitation. Since the UE-R recognizes that UE-R (itself) is not a DST UE, it broadcasts a corresponding discovery solicitation. Although Figure 5 It is shown that UE-2 also receives a discovery request from UE-1, but it is assumed that UE-2 receives the discovery request not from UE-1 but only from UE-R. UE-2 and UE-R reply with a discovery response. If multiple UE-Rs reply with corresponding discovery responses, UE-1 can select one of the multiple UE-Rs for relaying. Then, PC5 links for direct communication between UE-1 and UE-R and between UE-R and UE-2 and relaying of these direct communications at UE-R are created, so that a connection for U2U communication between UE-1 and UE-2 is established. According to alternative 2, the selection of the relay UE participating in the connection is performed in the direction from the SRC UE to the DST UE. Summary of the invention

[0084] The object of the present invention is to improve the prior art.

[0085] According to a first aspect of the present invention, there is provided a device, the device comprising:

[0086] one or more processors, and

[0087] a memory storing instructions that, when executed by the one or more processors, cause the apparatus to perform:

[0088] For each of the one or more terminal-to-terminal relay communications between the corresponding source terminal and the corresponding destination terminal:

[0089] - monitoring whether the relay terminal receives, at a respective first hop terminating at the relay terminal, a request to establish a first part of a connection for a respective terminal-to-terminal relay communication via the respective first hop, wherein the request includes the respective first local identifier;

[0090] - if the relay terminal receives the request, determining the corresponding second local identifier so that the corresponding second local identifier is unique among all local identifiers associated with the identifier of the corresponding second hop terminating at the relay terminal in the mapping table;

[0091] - storing the corresponding first mapping information mapped to the corresponding second mapping information in a mapping table, wherein the corresponding first mapping information includes an identifier of the corresponding first hop associated with the corresponding first local identifier, and the corresponding second mapping information includes an identifier of the corresponding second hop associated with the corresponding second local identifier; and

[0092] - a second part indicating establishment of a connection for a corresponding terminal-to-terminal relay communication via a corresponding second hop, wherein the indication includes a corresponding second local identifier;

[0093] supervising whether the relay terminal receives data of one of the one or more terminal-to-terminal relay communications including the third local identifier at an ingress hop terminating at the relay terminal;

[0094] If the relay terminal receives data of one of the one or more terminal-to-terminal relay communications including the third local identifier at an ingress hop, identifying fourth mapping information including an identifier of an egress hop associated with a fourth local identifier based on third mapping information including an identifier of the ingress hop associated with the third local identifier, wherein the fourth mapping information is mapped to the third mapping information in a mapping table, and the egress hop terminates at the relay terminal; and

[0095] Data of one of the one or more terminal-to-terminal relay communications including the fourth local identifier is forwarded on the egress hop.

[0096] When the instructions are executed by the one or more processors, the device may also execute:

[0097] monitoring whether the relay terminal receives a first command to form a first portion of a connection for a first terminal-to-terminal relay communication in one or more terminal-to-terminal relay communications via a fifth hop different from the second hop after the first portion of the connection for the first terminal-to-terminal relay communication is formed via the first hop, wherein the first command includes a fifth local identifier and the fifth hop terminates at the relay terminal;

[0098] The first mapping information for the first terminal-to-terminal relay communication is replaced with fifth mapping information in the mapping table, wherein the fifth mapping information includes an identifier of a fifth hop associated with a fifth local identifier.

[0099] When the instructions are executed by the one or more processors, the device may also execute:

[0100] monitoring whether the relay terminal receives a second command to form a second portion of a connection for a second terminal-to-terminal relay communication in the one or more terminal-to-terminal relay communications via a sixth hop different from the second hop after the second portion of the connection for the second terminal-to-terminal relay communication is formed via the second hop, wherein the sixth hop terminates at the relay terminal;

[0101] If the relay terminal receives the second command, determining a sixth local identifier such that the sixth local identifier is unique among all local identifiers associated with the identifier of the sixth hop in the mapping table;

[0102] replacing the second mapping information for the second terminal-to-terminal relay communication with sixth mapping information in the mapping table, wherein the sixth mapping information includes an identifier of a sixth hop associated with a sixth local identifier; and

[0103] Instructs establishment of a second portion of a connection for a second terminal-to-terminal relay communication via a corresponding sixth hop, wherein the instruction includes a sixth local identifier.

[0104] For at least one terminal-to-terminal relay communication among the one or more terminal-to-terminal relay communications:

[0105] The request to establish a first portion of a connection for a corresponding terminal-to-terminal relay communication via a corresponding first hop may include a first direct communication accept command; and

[0106] The indication to establish the second portion of the connection for the corresponding terminal-to-terminal relay communication via the corresponding second hop may include a second direct communication accept command.

[0107] For at least one terminal-to-terminal relay communication among the one or more terminal-to-terminal relay communications:

[0108] The request to establish a first portion of a connection for a corresponding device-to-device relay communication via a corresponding first hop may include a first direct communication request command; and

[0109] The instruction to establish a second portion of the connection for the corresponding terminal-to-terminal relay communication via the corresponding second hop may include a second direct communication request command.

[0110] For each terminal-to-terminal relay communication in one or more terminal-to-terminal relay communications, at least one of the following identifiers may be a layer 2 identifier of the corresponding neighboring terminal, or each of the following identifiers may be a layer 2 identifier of the corresponding neighboring terminal:

[0111] - the identifier of the corresponding first hop,

[0112] - the identifier of the corresponding second hop,

[0113] - the identifier of the corresponding third hop, or

[0114] - an identifier of the corresponding fourth hop;

[0115] The corresponding adjacent terminal is connected to the relay terminal via a corresponding one of a corresponding first hop, a corresponding second hop, a corresponding third hop, or a corresponding fourth hop.

[0116] For each of the one or more terminal-to-terminal relay communications, at least one of the following:

[0117] The corresponding first local identifier may be shorter than the layer 2 identifier; or

[0118] The corresponding second local identifier may be shorter than the layer 2 identifier.

[0119] When the instruction is executed by the one or more processors, the apparatus may further execute, for each of the one or more terminal-to-terminal relay communications:

[0120] The corresponding second local identifier is determined without regard to at least one of the following identifiers or without regard to any of the following identifiers:

[0121] - the identifier of the corresponding source terminal,

[0122] - the identifier of the corresponding destination terminal,

[0123] - the identifier of the corresponding first hop, or

[0124] - the corresponding first local identifier.

[0125] The data may include a protocol data unit of a sidelink relay adaptation layer for terminal-to-terminal relay communication, and a header of the protocol data unit may include a third local identifier.

[0126] According to a second aspect of the present invention, there is provided a device, the device comprising:

[0127] one or more processors, and

[0128] a memory storing instructions that, when executed by the one or more processors, cause the apparatus to perform:

[0129] For each of the one or more terminal-to-terminal relay communications between the first endpoint terminal and the corresponding second endpoint terminal:

[0130] - determining the respective first local identifier such that the respective first local identifier is unique among all local identifiers associated in the mapping table with the identifier of the respective first hop terminating at the first endpoint terminal;

[0131] - storing in the mapping table corresponding first mapping information mapped to the identifier of the corresponding terminal-to-terminal relay communication, wherein the corresponding first mapping information includes an identifier of the corresponding first hop associated with the corresponding first local identifier; and

[0132] - instructing establishment of a first part of a connection for a respective terminal-to-terminal relay communication via a respective first hop, wherein the indication comprises a respective first local identifier;

[0133] supervising whether the first endpoint terminal intends to send data of one of the one or more terminal-to-terminal relay communications to the corresponding second endpoint terminal;

[0134] If the first endpoint terminal intends to send data of one of the one or more terminal-to-terminal relay communications, identifying the identified mapping information based on an identifier of the one of the one or more terminal-to-terminal relay communications, the identified mapping information including an identifier of an egress hop associated with the identified local identifier, wherein the identified mapping information is mapped to the identifier of the one of the one or more terminal-to-terminal relay communications in a mapping table, and the egress hop terminates at the first endpoint terminal; and

[0135] Data of one of the one or more terminal-to-terminal relay communications including the identified local identifier is transmitted on the egress hop.

[0136] When the instructions are executed by the one or more processors, the device may also execute:

[0137] monitoring whether the first endpoint terminal intends to form a first portion of a connection for a first terminal-to-terminal relay communication of the one or more terminal-to-terminal relay communications via a second hop different from the first hop after the first portion of the connection for the first terminal-to-terminal relay communication is formed via the first hop, wherein the second hop terminates at the first endpoint terminal;

[0138] if the first endpoint terminal intends to form a first portion of a connection for the first terminal-to-terminal relay communication via the second hop, determining a second local identifier such that the second local identifier is unique among all local identifiers associated with an identifier of the second hop in the mapping table;

[0139] replacing the first mapping information with second mapping information in the mapping table, wherein the second mapping information includes an identifier of a second hop associated with the second local identifier; and

[0140] Instructions are provided to establish a first portion of a connection for the first terminal-to-terminal relay communication via a second hop, wherein the instructions include a second local identifier.

[0141] For each terminal-to-terminal relay communication in one or more terminal-to-terminal relay communications, at least one of the following identifiers may be a layer 2 identifier of the corresponding neighboring terminal, or each of the following identifiers may be a layer 2 identifier of the corresponding neighboring terminal:

[0142] - the identifier of the corresponding first hop, or

[0143] - Identifier of the egress hop;

[0144] The corresponding first hop or exit hop terminates at the corresponding adjacent terminal and the first endpoint terminal.

[0145] For each terminal-to-terminal relay communication of the one or more terminal-to-terminal relay communications:

[0146] The corresponding first local identifier may be shorter than the layer 2 identifier.

[0147] When the instruction is executed by the one or more processors, the apparatus may further execute, for each of the one or more terminal-to-terminal relay communications:

[0148] The corresponding first local identifier is determined without regard to at least one of the following identifiers or without regard to any of the following identifiers:

[0149] - an identifier of the first endpoint terminal,

[0150] - an identifier of the corresponding second endpoint terminal, or

[0151] - The identifier of the corresponding first hop.

[0152] For at least one terminal-to-terminal relay communication among the one or more terminal-to-terminal relay communications:

[0153] The first endpoint terminal may be a source terminal of a corresponding terminal-to-terminal relay communication; and

[0154] The instruction to establish a first portion of a connection for a corresponding terminal-to-terminal relay communication via a corresponding first hop may include a direct communication request command.

[0155] For at least one terminal-to-terminal relay communication among the one or more terminal-to-terminal relay communications:

[0156] The first endpoint terminal may be a destination terminal of a corresponding terminal-to-terminal relay communication; and

[0157] The instruction to establish a first portion of a connection for a corresponding terminal-to-terminal relay communication via a corresponding first hop may include a direct communication accept command.

[0158] According to a third aspect of the present invention, there is provided a method, the method comprising:

[0159] For each of the one or more terminal-to-terminal relay communications between the corresponding source terminal and the corresponding destination terminal:

[0160] - monitoring whether the relay terminal receives, at a respective first hop terminating at the relay terminal, a request to establish a first part of a connection for a respective terminal-to-terminal relay communication via the respective first hop, wherein the request includes the respective first local identifier;

[0161] - if the relay terminal receives the request, determining the corresponding second local identifier so that the corresponding second local identifier is unique among all local identifiers associated with the identifier of the corresponding second hop terminating at the relay terminal in the mapping table;

[0162] - storing the corresponding first mapping information mapped to the corresponding second mapping information in a mapping table, wherein the corresponding first mapping information includes an identifier of the corresponding first hop associated with the corresponding first local identifier, and the corresponding second mapping information includes an identifier of the corresponding second hop associated with the corresponding second local identifier; and

[0163] - a second part indicating establishment of a connection for a corresponding terminal-to-terminal relay communication via a corresponding second hop, wherein the indication includes a corresponding second local identifier;

[0164] supervising whether the relay terminal receives data of one of the one or more terminal-to-terminal relay communications including the third local identifier at an ingress hop terminating at the relay terminal;

[0165] If the relay terminal receives data of one of the one or more terminal-to-terminal relay communications including the third local identifier at an ingress hop, identifying fourth mapping information including an identifier of an egress hop associated with a fourth local identifier based on third mapping information including an identifier of the ingress hop associated with the third local identifier, wherein the fourth mapping information is mapped to the third mapping information in a mapping table, and the egress hop terminates at the relay terminal; and

[0166] Data of one of the one or more terminal-to-terminal relay communications including the fourth local identifier is forwarded on the egress hop.

[0167] The method may further include:

[0168] monitoring whether the relay terminal receives a first command to form a first portion of a connection for a first terminal-to-terminal relay communication in one or more terminal-to-terminal relay communications via a fifth hop different from the second hop after the first portion of the connection for the first terminal-to-terminal relay communication is formed via the first hop, wherein the first command includes a fifth local identifier and the fifth hop terminates at the relay terminal;

[0169] The first mapping information for the first terminal-to-terminal relay communication is replaced with fifth mapping information in the mapping table, wherein the fifth mapping information includes an identifier of a fifth hop associated with a fifth local identifier.

[0170] The method may further include:

[0171] monitoring whether the relay terminal receives a second command to form a second portion of a connection for a second terminal-to-terminal relay communication in the one or more terminal-to-terminal relay communications via a sixth hop different from the second hop after the second portion of the connection for the second terminal-to-terminal relay communication is formed via the second hop, wherein the sixth hop terminates at the relay terminal;

[0172] If the relay terminal receives the second command, determining a sixth local identifier such that the sixth local identifier is unique among all local identifiers associated with the identifier of the sixth hop in the mapping table;

[0173] replacing the second mapping information for the second terminal-to-terminal relay communication with sixth mapping information in the mapping table, wherein the sixth mapping information includes an identifier of a sixth hop associated with a sixth local identifier; and

[0174] Instructs establishment of a second portion of a connection for a second terminal-to-terminal relay communication via a corresponding sixth hop, wherein the instruction includes a sixth local identifier.

[0175] For at least one terminal-to-terminal relay communication among the one or more terminal-to-terminal relay communications:

[0176] The request to establish a first portion of a connection for a corresponding terminal-to-terminal relay communication via a corresponding first hop may include a first direct communication accept command; and

[0177] The indication to establish the second portion of the connection for the corresponding terminal-to-terminal relay communication via the corresponding second hop may include a second direct communication accept command.

[0178] For at least one terminal-to-terminal relay communication among the one or more terminal-to-terminal relay communications:

[0179] The request to establish a first portion of a connection for a corresponding device-to-device relay communication via a corresponding first hop may include a first direct communication request command; and

[0180] The instruction to establish a second portion of the connection for the corresponding device-to-device relay communication via the corresponding second hop may include a second direct communication request command.

[0181] For each terminal-to-terminal relay communication in one or more terminal-to-terminal relay communications, at least one of the following identifiers may be a layer 2 identifier of the corresponding neighboring terminal, or each of the following identifiers may be a layer 2 identifier of the corresponding neighboring terminal:

[0182] - the identifier of the corresponding first hop,

[0183] - the identifier of the corresponding second hop,

[0184] - the identifier of the corresponding third hop, or

[0185] - an identifier of the corresponding fourth hop;

[0186] The corresponding adjacent terminal is connected to the relay terminal via a corresponding one of a corresponding first hop, a corresponding second hop, a corresponding third hop, or a corresponding fourth hop.

[0187] For each of the one or more terminal-to-terminal relay communications, at least one of the following:

[0188] The corresponding first local identifier may be shorter than the layer 2 identifier; or

[0189] The corresponding second local identifier may be shorter than the layer 2 identifier.

[0190] Determining the corresponding second local identifier may be performed without regard to at least one of the following identifiers or without regard to any of the following identifiers:

[0191] - the identifier of the corresponding source terminal,

[0192] - the identifier of the corresponding destination terminal,

[0193] - the identifier of the corresponding first hop, or

[0194] - the corresponding first local identifier.

[0195] The data may include a protocol data unit of a sidelink relay adaptation layer for terminal-to-terminal relay communication, and a header of the protocol data unit may include a third local identifier.

[0196] According to a fourth aspect of the present invention, there is provided a method, the method comprising:

[0197] For each of the one or more terminal-to-terminal relay communications between the first endpoint terminal and the corresponding second endpoint terminal:

[0198] - determining the respective first local identifier such that the respective first local identifier is unique among all local identifiers associated in the mapping table with the identifier of the respective first hop terminating at the first endpoint terminal;

[0199] - storing in the mapping table corresponding first mapping information mapped to the identifier of the corresponding terminal-to-terminal relay communication, wherein the corresponding first mapping information includes an identifier of the corresponding first hop associated with the corresponding first local identifier; and

[0200] - instructing establishment of a first part of a connection for a respective terminal-to-terminal relay communication via a respective first hop, wherein the indication comprises a respective first local identifier;

[0201] supervising whether the first endpoint terminal intends to send data of one of the one or more terminal-to-terminal relay communications to the corresponding second endpoint terminal;

[0202] If the first endpoint terminal intends to send data of one of the one or more terminal-to-terminal relay communications, identifying the identified mapping information based on an identifier of the one of the one or more terminal-to-terminal relay communications, the identified mapping information including an identifier of an egress hop associated with the identified local identifier, wherein the identified mapping information is mapped to the identifier of the one of the one or more terminal-to-terminal relay communications in a mapping table, and the egress hop terminates at the first endpoint terminal; and

[0203] Data of one of the one or more terminal-to-terminal relay communications including the identified local identifier is transmitted on the egress hop.

[0204] The method may further include:

[0205] monitoring whether the first endpoint terminal intends to form a first portion of a connection for a first terminal-to-terminal relay communication of the one or more terminal-to-terminal relay communications via a second hop different from the first hop after the first portion of the connection for the first terminal-to-terminal relay communication is formed via the first hop, wherein the second hop terminates at the first endpoint terminal;

[0206] if the first endpoint terminal intends to form a first portion of a connection for the first terminal-to-terminal relay communication via the second hop, determining a second local identifier such that the second local identifier is unique among all local identifiers associated with an identifier of the second hop in the mapping table;

[0207] replacing the first mapping information with second mapping information in the mapping table, wherein the second mapping information includes an identifier of a second hop associated with the second local identifier; and

[0208] Instructions are provided to establish a first portion of a connection for the first terminal-to-terminal relay communication via a second hop, wherein the instructions include a second local identifier.

[0209] For each terminal-to-terminal relay communication in one or more terminal-to-terminal relay communications, at least one of the following identifiers may be a layer 2 identifier of the corresponding neighboring terminal, or each of the following identifiers may be a layer 2 identifier of the corresponding neighboring terminal:

[0210] - the identifier of the corresponding first hop, or

[0211] - Identifier of the egress hop;

[0212] The corresponding first hop or exit hop terminates at the corresponding adjacent terminal and the first endpoint terminal.

[0213] For each terminal-to-terminal relay communication of the one or more terminal-to-terminal relay communications:

[0214] The corresponding first local identifier may be shorter than the layer 2 identifier.

[0215] Determining the corresponding first local identifier may be performed without regard to at least one of the following identifiers or without regard to any of the following identifiers:

[0216] - an identifier of the first endpoint terminal,

[0217] - an identifier of the corresponding second endpoint terminal, or

[0218] - The identifier of the corresponding first hop.

[0219] For at least one terminal-to-terminal relay communication among the one or more terminal-to-terminal relay communications:

[0220] The first endpoint terminal may be a source terminal of a corresponding terminal-to-terminal relay communication; and

[0221] The instruction to establish a first portion of a connection for a corresponding terminal-to-terminal relay communication via a corresponding first hop may include a direct communication request command.

[0222] For at least one terminal-to-terminal relay communication among the one or more terminal-to-terminal relay communications:

[0223] The first endpoint terminal may be a destination terminal of a corresponding terminal-to-terminal relay communication; and

[0224] The instruction to establish a first portion of a connection for a respective terminal-to-terminal relay communication via a respective first hop may include a direct communication accept command.

[0225] Each of the methods of the third aspect and the fourth aspect may be a method of U2U relay communication.

[0226] According to a fifth aspect of the present invention, a computer program product is provided, the computer program product comprising an instruction set, which, when executed on a device, is configured to cause the device to perform a method according to any of the third and fourth aspects. The computer program product may be embodied as a computer readable medium or may be directly loadable into a computer.

[0227] According to some embodiments of the present invention, at least one of the following advantages can be achieved:

[0228] The protocol overhead in U2U relay communication can be reduced;

[0229] Delays can be minimized;

[0230] The additional signaling effort may be small;

[0231] Multi-hop U2U relay can be supported;

[0232] • Robustness against modifications to the L2 ID of any UE involved in the E2E communication.

[0233] It should be understood that any of the above modifications may be applied alone or in combination to the corresponding aspects to which they refer, unless they are explicitly stated to exclude alternatives. BRIEF DESCRIPTION OF THE DRAWINGS

[0234] Additional details, features, objects and advantages will be apparent from the following detailed description of preferred embodiments of the present invention taken in conjunction with the accompanying drawings, in which:

[0235] Figure 1 The user plane protocol stack for L2 UE to UE relay (according to 3GPP TR 38.836, Figure 5 .5.1-1);

[0236] Figure 2 The control plane protocol stack for L2 UE to UE relay (according to 3GPP TR 38.836, Figure 5 .5.1-2);

[0237] Figure 3 The SRAP data PDU format with SRAP header for U2N relay is shown (according to 3GPP TS38.351, Figure 6 .2.2-1);

[0238] Figure 4 5G ProSe UE to UE relay selection, Alternative 1 (according to 3GPP TR 23.700-33, Figure 6 .1.2.1-1);

[0239] Figure 5 5G ProSe UE-to-UE relay selection, Alternative 2 (according to 3GPP TR 23.700-33, Figure 6 .1.2.2-1)

[0240] Figure 6 shows a message sequence chart according to some example embodiments of the present invention;

[0241] Figure 7 shows a message sequence chart according to some example embodiments of the present invention;

[0242] FIG8 illustrates establishment of a connection for multiple U2U relay communications according to some example embodiments of the present invention;

[0243] Fig. 9 An apparatus according to an example embodiment of the present invention is shown;

[0244] Fig.10 A method according to an example embodiment of the present invention is shown;

[0245] Fig.11 An apparatus according to an example embodiment of the present invention is shown;

[0246] Fig.12 A method according to an example embodiment of the present invention is shown; and

[0247] Fig.13 An apparatus according to an example embodiment of the invention is shown. DETAILED DESCRIPTION

[0248] Hereinafter, some embodiments of the present invention will be described in detail with reference to the accompanying drawings, wherein the features of the embodiments may be freely combined with each other unless otherwise described. However, it should be clearly understood that the description of some embodiments is given by way of example only and is by no means intended to be understood as limiting the present invention to the disclosed details.

[0249] Furthermore, it should be understood that the apparatus is configured to perform the corresponding method, although in some cases only the apparatus or only the method is described.

[0250] Some example embodiments of the present invention may solve or overcome the technical problem of how to include identity information of a source remote UE (also referred to herein as a source UE) and / or identity information of a destination remote UE (also referred to herein as a destination UE) into an adaptation layer.

[0251] It is known from the studies on SL relay and the specification of Rel-17 L2 U2N relay that it is preferable to allocate short IDs for SRC UE and DST UE for addressing the corresponding UE in the L2 relay adaptation layer, rather than using existing IDs (such as ProSe L2 ID, C-RNTI or TMSI of the corresponding UE). The short ID may be similar to the local ID of the remote UE that is allocated to the serving relay UE unique to the Rel-17 L2 U2N relay. Allocating short IDs is preferable because multiplexing of data from different SRC UEs or DST UEs (remote UEs in L2 U2N relay) is supported in L2 U2U relay (L2 U2N relay), and using short IDs ( Figure 3 The 8-bit UE ID for L2 U2N relay shown in FIG. 10 ) can significantly reduce the protocol overhead.

[0252] In U2U relay, a SRC UE may use the same serving U2U relay UE to connect to different DST UEs, or different SRC UEs may also use the same serving U2U relay UE to connect to the same DST UE. In the former case, for the direction from SRC UE to DST UE, it is possible to multiplex data from the same SRC UE to different DST UEs at the SRC UE or a serving U2U relay UE other than the last hop serving U2U relay UE on the L2 U2U relay adaptation layer. For the direction from DST UE to SRC UE, it is possible to multiplex data from different DST UEs to the same SRC UE at (multiple) serving U2U relay UEs on the L2 U2U relay adaptation layer. In the latter case, similar multiplexing of data to / from the same DST UE is possible.

[0253] In Rel-17 L2 U2N relay, the local ID of the remote UE is locally unique for the serving L2 U2N relay UE. The local ID is assigned to both the remote UE and the relay UE by the serving gNB using, for example, the RRC reconfiguration procedure (see 3GPP TS 38.331). In L2U2U relay, the gNB (or another centralized control entity) may not assign such a local ID because L2U2U communication is not centrally controlled.

[0254] In order to explain some example embodiments of the present invention, some terms are first explained. A "hop" is a direct connection between two UEs. That is, via a hop, the UEs at the endpoints of the hop can communicate directly with each other via a PC5 link. At each endpoint of the hop, the hop can be specified by the ID of the other endpoint. However, in some example embodiments, the hop can be identified by a hop ID, which can be explicitly mapped to the ID of the other endpoint.

[0255] U2U relay communication passes through at least two hops. Each hop forms part of the connection for U2U relay communication. UEs in the middle of the U2U relay communication relay direct communications that terminate at the hops of these UEs.

[0256] In order to create (establish) U2U relay communication, any of the alternatives 1 and 2 discussed in the prior art section may be used. That is, the endpoints of the U2U relay communication may be designated as the SRC UE and the DST UE, wherein the SRC UE initiates the creation of a connection for the U2U relay communication. According to alternative 1, the DST UE selects a hop to a relay UE, which then selects a hop to another relay UE or SRC UE, etc. In order to establish direct communication on the hop, a DCA is sent on the corresponding hop in the direction from the DST UE to the SRC UE.

[0257] For alternative 2, the SRC UE selects a first relay UE, which in turn selects another relay UE or a DST UE, etc. In this alternative, the DCR is used to establish direct communication on the corresponding hop.

[0258] According to some example embodiments, on each of the hops forming the U2U relay communication, a local ID (LID) identifies a different U2U relay communication. Each LID is unique on the corresponding hop. That is, if there are two U2U relay communications on the hop, the two U2U relay communications have different LIDs on the corresponding hop. However, on different hops of the U2U relay communication, different LIDs or the same LID may be assigned to the U2U relay communication.

[0259] At one UE, the same LID may be used on different hops. For example, the same LID may be used for the same U2U relay communication on a hop towards an SRC UE and on a hop towards a DST UE, and / or the same LID may be used on different hops for different U2U relay communications through the UE.

[0260] Each relay UE maintains a mapping table in which mapping information of different fragments are mapped to each other. For each U2U relay communication in the U2U relay communication, the mapping information maps the first mapping information with the second mapping information. The first mapping information includes an ID of a hop terminated at the corresponding UE, and the hop forms part of a connection for the U2U relay communication associated with the LID of the U2U relay communication on the hop. The second mapping information includes an ID of another hop terminated at the UE, and the other hop forms part of a connection for the U2U relay communication associated with the LID of the U2U relay communication on the other hop.

[0261] Each endpoint UE (SRC UE, DST UE) of the U2U relay communication also maintains a mapping table in which the first mapping information (as described in the previous paragraph) is mapped to the identifier of the U2U relay communication.

[0262] Since the UE can be both a relay UE of one U2U relay communication and an endpoint UE of another U2U relay communication, the UE can maintain both mapping tables. In this case, the two mapping tables can be regarded as one (combined) mapping table.

[0263] If U2U relay communication is created, each of the SRC UE and the DST UE can send data of the U2U relay communication via the created connection. That is, accordingly, the SRC UE can be a TX UE or a RX UE, and the DST UE can be a RX UE or a TX UE. When the TX UE sends data to the RX UE via the U2U relay communication, the TX UE includes the LID of the U2U relay communication for the jump terminating at the TX UE into, for example, the PDU of the L2U2U side link relay adaptation protocol sublayer (preferably into its header). The relay UE at the other end point of the jump identifies the ID of the TX UE and the LID included in the PDU. In the mapping table of the relay UE, the combination is mapped to the ID of another link and the LID of the U2U relay communication for the other link. Therefore, the relay UE forwards data on the other link and includes the LID for the other link into the PDU instead of the LID received from the SRC UE. This process continues until the data reaches the RX UE.In some example embodiments, the LID may be omitted on the last hop to the RX UE.

[0264] Figure 6 The diagram illustrates the establishment of a connection for U2U relay communication between a SRC UE and a DST UE according to some example embodiments of the present invention. Figure 6 As shown in , the SRC UE determines to initiate a DCR towards the DST UE. In the DCR, it is indicated that relaying is acceptable. The SRC UE broadcasts the DCR, which includes the ID of the SRC UE (such as the L2 ID of the SRC UE). The DCR also includes the ID of the DST UE. The ID can be the L2 ID of the DST UE or the ID of the DST UE of a higher layer.

[0265] The DCR broadcast by the SRC UE is received by the U2U relay UE1, but not by the DST UE. The U2U relay UE1 understands that the DCR is not intended for itself, and broadcasts another DCR. The DCR includes the ID of the U2U relay UE1 (such as the L2ID of the UE), and again includes the ID of the DST UE. Figure 6In the example of , the process is repeated at U2U relay UE2. Finally, the DST UE receives the DCR. Potentially, the DST UE receives the DCR from different relay UEs. In this case, the DST UE selects one of the relay UEs, from which the DST UE receives the DCR for the first hop. Therefore, the DST UE replies to the DCR via a DCA. The DCA not only includes the L2 ID of the SRC ID and the L2 ID of the DST UE, but also additionally includes a LID (LID#3), which specifies the U2U relay communication between the SRC UE and the DST UE, on the hop between the DST UE and the selected U2U relay UE2. LID#3 is unique on the hop between the DST UE and the U2U relay UE2.

[0266] Correspondingly, the U2U relay UE2 may have received DCRs from multiple U2U relay UE1s. Therefore, the U2U relay UE2 selects one U2U relay UE1 among the multiple U2U relay UE1s and sends a DCA to the selected U2U relay UE1. The DCA again includes the L2 ID of the SRC UE and the L2 ID of the DST UE (which specifies a specific U2U relay communication) and LID#2. LID#2 is unique on the hop between the U2U relay UE2 and the U2U relay UE1. The U2U relay UE2 maintains a record in a mapping table, which includes an ID of a hop between the U2U relay UE2 and the DST UE associated with LID#3, which is mapped to an ID of a hop between the U2U relay UE2 and the U2U relay UE1 associated with LID#2. LID#3 and LID#2 may be the same as or different from each other. A corresponding process is performed on the U2U relay UE1, which selects a hop to the SRC UE and includes LID#1 into the DCA for the SRC ID. LID#1 is unique across the hops between the SRC UE and the U2U relay UE1. The U2U relay UE1 maintains a mapping table, which includes a record including an ID of a hop between the U2U relay UE1 and the U2U relay UE2 associated with LID#2, the ID of the hop being mapped to an ID of a hop between the SRC UE and the U2U relay UE1 associated with LID#1.

[0267] The SRC UE and DST UE store the ID of the U2U relay communication (which may be the ID of the other of the SRC UE and the DST UE (such as the L2 ID)) in their respective mapping tables, which is mapped together with the LID of the corresponding link (LID#1 on the SRC UE, LID#3 on the DST UE) to the ID of the corresponding link terminating at the SRC UE and the DST UE respectively.

[0268] Figure 7 A message sequence diagram of Alternative Solution 2 according to some example embodiments of the present invention is shown. Figure 7 As shown in , the SRC UE first performs discovery of the DST UE and discovery of U2U relay UE candidates to reach the DST UE. Then, the SRC UE selects a hop (to the U2U relay UE1) and assigns LID#1 to the U2U relay communication for the hop. LID#1 is unique on the hop between the SRC UE and the U2U relay UE1. The SRC UE sends a DCR to the selected U2U relay UE1, which includes LID#1 and the L2 ID of the SRC UE and the L2 ID of the DST UE. Correspondingly, the U2U relay UE1 selects the U2U relay UE2 and determines LID#2, which is unique on the hop between the U2U relay UE 1 and the U2U relay UE2. The U2U relay UE1 sends a DCR to the selected U2U relay UE2, which includes LID#2 and the L2 ID of the SRC UE and the L2 ID of the DST UE. U2U relay UE2 performs operations corresponding to U2U relay UE1 and allocates LID#3, which is unique on the next hop (ie, the hop between U2U relay UE2 and DST UE). Then, U2U relay UE2 sends a DCR to the DST UE, wherein the DCR includes LID#3.

[0269] U2U relay UE1 and U2U relay UE2 each maintain a mapping table, which includes a record for a specific U2U relay communication. In the record, U2U relay UE1 and U2U relay UE2 store the ID of the hop used in the U2U relay communication and terminated at the relay UE, each associated with its corresponding LID. In the SRC UE and DST UE, the corresponding mapping table includes: the ID of the U2U relay communication (such as the L2 ID of the other of the SRC UE and the DST UE) is mapped to the mapping between the ID of the hop, which is terminated at the corresponding one of the SRC UE and the DST UE associated with the LID used for the U2U relay communication on the hop.

[0270] Note that in both Alternative 1 and Alternative 2, the corresponding UE can determine one of the LIDs completely independently of any UE ID (such as the ID of other relay UEs, the ID of the SRC UE, or the ID of the DST UE). The only condition that the corresponding UE must comply with is that each of the LIDs on the corresponding hop is unique on that corresponding hop.

[0271] When the connection for U2U relay communication is established, each of the SRC UE and the DST UE can transmit data to the other of the SRC UE or the DST UE via the U2U relay communication. Figure 6 The example of is explained for the case where the SRC UE sends data to the DST UE. That is, the SRC UE is the TX UE and the DST UE is the RX UE. In this case, the SRC UE sends data on the hop to the U2U relay UE1 in direct U2U communication. The PDU carrying data on the U2U SRAP sublayer includes LID#1 (for example, the local UE ID field in the header of the PDU is set to LID#1). The U2U relay UE1 understands that the PDU is received from the SRC UE on the hop and includes LID#1. In the mapping table of the U2U relay UE1, the ID of the hop to the U2U relay UE2 and LID#2 are mapped to the combination of the ID of the hop to the SRC UE and LID#1. Therefore, the U2U relay UE1 forwards the received PDU to the U2U relay UE2, where LID#1 is replaced by LID#2.

[0272] U2U relay UE2 understands that it received a PDU from U2U relay UE1 on a hop and that the PDU includes LID#2. In the mapping table of U2U relay UE2, the combination of hop ID and LID is mapped to the hop of the DST UE associated with LID#3. Therefore, U2U relay UE2 forwards the PDU on the hop to the DST UE in direct U2U communication and replaces LID#2 with LID#3 in the PDU. Therefore, the data finally reaches the DST UE.

[0273] In a system including multiple UEs, each UE may be a SRC UE or a DST UE or a relay UE for a specific U2U relay communication. In addition, in such a system, the connection of each relay communication may be established through alternative 1 or alternative 2. An example of such a system is shown in FIG8 , which includes Figures 8a to 8c . In this example, each UE from UE1 to UE4 is connected to each of the other UEs from UE1 to UE4 via one or more relay UEs from relay UE UE-R1 to relay UE UE-R3. In Figure 8, the hop is specified by the number of the endpoint of the hop (i.e., hop 1-R1 represents the hop between UE1 and UE-R1), and the U2U relay communication is specified by Cxy, where x and y are the numbers of the endpoints of the U2U relay communication. For example, C13 represents U2U relay communication between UE1 and UE3. Figures 8a to 8c In each of the figures, two U2U relay communications are additionally created, indicated by the thick dashed lines.

[0274] like Figure 8a As shown in , the connection for communication C13 and communication C24 has been established. UE1 is the SRC for C13. Alternative 2 is used. Therefore, UE1 assigns LID=1 to C13 on hop 1-R1 in the DCR message. UE-R1 sends a DCR to UE-2, where LID=1 is associated with C13 on hop R1-R2. Correspondingly, UE-R2 sends a DCR to UE-R3 with LID=1. Finally, UE-R3 sends a DCR to UE3 with LID=1 for C13. Therefore, C13 is established.

[0275] Then, C24 is established when UE2=SRC UE and UE4=DST UE. Alternative 2 is used. UE2 can assign any LID for communication C24 on hop 2-R1. In this case, LID=2 is determined by UE2. However, UE-R1 cannot freely determine the LID for C24 on the hop to UE-R2 because LID=1 has been used for communication C13. Therefore, UE-R1 determines LID=4 for C24 on hop R1-R2. Correspondingly, UE-R2 cannot freely determine the LID for C24 on hop R2-R3 because LID=1 has been used by C13 on the hop. Therefore, UE-R2 determines LID=4 for C24 on hop R2-R3. UE-R3 can select any LID for communication C24 for hop R3-4. In this example, UE-R3 determines LID=1. Therefore, the connection for U2U relay communication C24 is also established.

[0276] In this example, after the establishment of C13 and C24, C14 and C23 are established, as shown in FIG. Figure 8b As shown in . In this case, once again, UE1 and UE2 are SRC UEs, and UE3 and UE4 are DST UEs. However, in these cases, for the purpose of establishment, alternative 1 is used. Specifically as follows:

[0277] To establish C23, UE3 cannot freely determine the LID on hop R3-3 because LID=1 is used for C13 on that hop. Therefore, UE3 determines LID=2 for C23 on hop R3-3. This LID is provided to UE-R3 by DCA. UE-R3 cannot freely determine the LID for C23 on hop R2-R3 because LID 1 and LID 4 are already used for C13 and C24 on that hop. Therefore, UE-R3 determines LID=3 for C23 on hop R2-R3. Correspondingly, UE-R2 determines LID=3 for C23 on hop R1-R2, and UE-R1 determines LID=1 for C23 on hop 2-R1.

[0278] Correspondingly, the corresponding LID is allocated to C14 on the corresponding hop between UE1 and UE4.

[0279] like Figure 8c As shown in , C12 and C34 are established. In C12, UE1 is a SRC UE and UE2 is a DST UE. Alternative 1 is used. Therefore, UE2 determines a LID different from 1 and 2 that have been used on hop 2-R1 for C12 on hop 2-R1 (here: LID=7). UE-R1 determines LID=7 for C12 on hop 1-R1. This LID is different from 1 and 2 that have been used on hop 1-R1.

[0280] To establish U2U relay communication C34, UE3 is a SRC UE and UE4 is a DST UE. Alternative 2 is used. Therefore, UE3 determines LID=3 for C34 on hop R3-3. UE-R3 determines LID=5 for C34 on hop R3-4. Therefore, further connections for communication C12 and communication C34 are established.

[0281] Table 1 shows Figure 8c UE-R1 in the example. Note that the mapping table of the relay UE does not need to store the identifier of the corresponding U2U relay communication for each record. Table 2 shows the mapping table for Figure 8c The mapping table of UE1 in the example of FIG. In the mapping table, U2U relay communication is identified and mapped to a certain combination of hop ID and LID.

[0282] Link ID Local ID Link ID Local ID 1-R1 1 R1-R2 1 1-R1 2 R1-R2 7 1-R1 7 2-R1 7 2-R1 1 R1-R2 3 2-R1 2 R1-R2 4

[0283] Table 1: Figure 8c The mapping table of UE-R1 in the example

[0284]

[0285]

[0286] Table 2: Figure 8c The mapping table of UE1 in the example

[0287] If reselection of the relay UE in U2U relay communication is performed, this may not affect the end-to-end connection. That is, in this case, the corresponding hops and the corresponding LIDs can be exchanged in the mapping table. However, the direction of allocating the LID is the same as when it was originally established (i.e., from the DST UE to the SRC UE in Alternative 1, and from the SRC UE to the DST UE in Alternative 2). Note that in a multi-hop U2U relay connection, the reselection of the serving U2U relay UE may not have an end-to-end impact on any one of the SRC UE and the DST UE. However, the reselection of the serving U2U relay UE in a two-hop U2U relay connection has an end-to-end impact on both the SRC UE and the DST UE. In this case, the reallocation of the LID can be regarded as a new allocation.

[0288] LID is used by SRC UE, DST UE and serving U2U relay UE on the U2U relay adaptation layer for SL U2U relay-based data transmission in both directions: from SRC UE to DST UE (SRC UE=TX UE, DST UE=RX UE) and from DST UE to SRC UE (DST UE=TX UE, SRCUE=RX UE).

[0289] In some example embodiments, a SRC UE, a DST UE, or one of the serving U2U relay UEs may initiate a local reallocation of a local ID that it has allocated for one of the hops that form part of the connection for the U2U relay communication (the hop towards the SRC UE in the case of alternative 1, and the hop towards the DST UE in the case of alternative 2). Such a reallocation may be useful, for example, for some preferred local ID alignment. Again, in this case, the initiating UE must take care that the new local ID is unique among the local IDs for that one of the hops.

[0290] In some example embodiments using alternative 2, the SRC UE may be configured to determine whether to initiate local ID allocation when starting L2 E2E connection establishment towards the DST UE. For example, the unicast DCR to the next selected U2U relay UE may include a corresponding flag. As another option, the relay UE may understand that local ID allocation is required if the unicast DCR command includes a local ID, and that local ID allocation is not required if the unicast DCR command does not include a local ID.

[0291] In some example embodiments using alternative 1, the DST UE may be configured to determine whether to initiate local ID allocation when selecting a U2U relay UE among those candidates from which a DCR message originating from the SRC UE is received. The corresponding DCA may include a corresponding flag. As another option, the relay UE may understand that local ID allocation is required if the unicast DCA command includes a local ID, and that local ID allocation is not required if the unicast DCA command does not include a local ID.

[0292] In some example embodiments, any one of the SRC UE, DST UE, or one of the serving U2U relay UEs may initiate: a request for E2E reallocation or E2E connection re-creation of a local ID towards the SRC UE or DST UE. This may be triggered, for example, in the case of performing a local U2U relay reselection applied to one or more serving U2U relay UEs in a multi-hop U2U relay, which may not cause E2E impact to the SRC UE and DST UE (as described above), but for some reason, takes longer than expected (e.g., a pre-configured timer protecting such an event expires) or there is no expected local ID reallocation.

[0293] In some example embodiments, SL HARQ with feedback is used to allocate a local ID on the egress hop or, i.e., to send a unicast DCR or DCA in which the local ID is included for local ID allocation. As another option to ensure that the LID is reliably sent on the corresponding hop, a local immediate acknowledgement at a higher layer on the hop for such a DCR or DCA may be used. As yet another option, any measures to ensure that the UE at the other terminating end of the hop reliably receives the LID may be omitted.

[0294] In some example embodiments, a U2U relay UE serving an E2E connection for U2U relay communication between an SRC UE and a DST UE in a multi-hop U2U relay indicates to the previous hop U2U relay UE for the U2U relay communication the ProSe L2 ID of the next hop U2U relay UE for the U2U relay communication. The "next hop" and "previous hop" here indicate the hop in the direction of creating the connection (from the DST UE to the SRC UE in the case of alternative 1, and from the SRC UE to the DST UE in the case of alternative 2). Therefore, local coordination between the previous hop U2U relay UE and the next hop U2U relay UE is enabled for local U2U relay reselection of the U2U relay UE and / or local ID reallocation with no E2E impact on both the SRC UE and the DST UE.

[0295] In another (corresponding) option according to some example embodiments, the relay UE may not know that the relay UE terminates the next (or previous) hop. However, the relay UE knows the SRC UE and the DST UE of the communication. If a first relay UE (e.g., UE-R1 in the communication path SRC UE—UE-R1—UE-R2—UE-R3—UE-R4—DST UE) wants to reselect a relay UE (e.g., UE-R2) of one of the hops that terminate the communication (e.g., because the hop is interrupted), the first relay UE may broadcast a DCR to indicate that the request is for communication between the SRC UE and the DST UE, and that the hop is for a direction toward the SRC UE or toward the DST UE, respectively. Potentially, the DCR may be forwarded by one or more candidate relay UEs until the serving relay UE (e.g., UE-R3) that has relayed communication between the SRC UE and the DST UE receives the (potentially forwarded) DCR. UE-R3 may respond to the DCR with a DCA, which may be forwarded to UE-R1 (if necessary). UE-R1 may thus replace the hop to UE-R2 with one or more other hops, such that the hop chain terminates at UE-R3. This reallocation has no effect outside the communication path between UE-R1 and UE-R3 (in particular: at the SRC UE and the DST UE). Note that in this example, UE-R1 may receive multiple DCA messages, i.e., from the same "UE-R3" via different communication paths (hop chains) between UE-R3 and UE-R1, and / or from different service relay UEs (e.g., UE-R3 and UE-R4) that were initially involved in the communication path between the SRC UE and the DST UE. In such a case, UE-R1 may select one of the corresponding communication paths. This option may be robust in finding a suitable communication path, but may result in significant overhead because it may not keep the reselection of the U2U relay UE local to the U2U relay UE's immediate previous hop U2U relay UE and the next hop U2U relay UE.

[0296] The local ID allocation according to some example embodiments of the present invention is robust against the modification of the ProSe L2 ID at the SRC UE, DST UE, or serving U2U relay UE. That is, the modification of the ProSe L2 ID at any UE involved in the L2 E2E connection between the SRC UE and the DST UE will not result in a change in the allocated local ID (and vice versa).

[0297] The local ID may be shorter than the ID (e.g., L2 ID) of the SRC UE and DST UE, or the ID of the serving relay UE where the corresponding hop terminates. For example, if the L2 ID of the UE has 24 bits, the local ID of the U2U relay communication on the hop may have 23 bits or less, for example, 8 bits as the local ID of the remote UE in the L2 U2N relay, such as Figure 3 Preferably, the local ID of the U2U relay communication on the hop has significantly fewer bits (at least 3 bits less) than any UE ID that can be used in the mapping. For example, if the number of U2U relay communications on the hop is limited to 2 n-1 +1 to 2 n If the local ID is between , the local ID may have n bits (eg, n=3, or n=4, or n=5, or n=6, or n=7).

[0298] Some exemplary embodiments of the present invention have at least one of the following technical advantages:

[0299] (i) avoiding involving many (or even all) U2U relay UE candidates along different paths for E2E SL connection between SRC UE and DST UE in local ID allocation. Thus, protocol overhead is minimized; and / or

[0300] (ii) Allocate a local ID as soon as possible. Therefore, the U2U SL adaptation function is enabled to use a local ID with minimum delay along the selected path for the E2E SL connection between the SRC UE and the DST UE via the serving U2U relay UE.

[0301] Fig. 9 An apparatus according to an exemplary embodiment of the present invention is shown. The apparatus may be a terminal, such as a UE (particularly a relay UE for U2U relay communication), or an element thereof. Fig.10 A method according to an exemplary embodiment of the present invention is shown. Fig. 9 The device can perform Fig.10 method, but not limited to this method. Fig.10 The method can be Fig. 9 The present invention is performed by a device, but is not limited to being performed by the device.

[0302] The apparatus comprises a component 110 for monitoring, a component 120 for determining, a component 130 for storing, a component 140 for indicating, a component 150 for supervising, a component 160 for identifying, and a component 170 for forwarding. The component 110 for monitoring, the component 120 for determining, the component 130 for storing, the component 140 for indicating, the component 150 for supervising, the component 160 for identifying, and the component 170 for forwarding may be a monitoring component, a determining component, a storage component, an indicating component, a supervising component, an identifying component, and a forwarding component, respectively. The component 110 for monitoring, the component 120 for determining, the component 130 for storing, the component 140 for indicating, the component 150 for supervising, the component 160 for identifying, and the component 170 for forwarding may be a monitor, a determiner, a storage device, an indicator, a supervisor, an identifier, and a forwarder, respectively. The component 110 for monitoring, the component 120 for determining, the component 130 for storing, the component 140 for indicating, the component 150 for supervising, the component 160 for identifying, and the component 170 for forwarding may be a monitoring processor, a determining processor, a storing processor, an indicating processor, a supervising processor, an identifying processor, and a forwarding processor, respectively.

[0303] S110 to S140 are performed for each U2U relay communication ("terminal to terminal relay communication") to create a connection for the U2U relay communication. Each U2U relay communication in the U2U relay communication is defined by a corresponding source UE and a corresponding destination UE. S110 to S140 are described below for one U2U relay communication in the U2U relay communication.

[0304] The monitoring component 110 monitors whether the relay terminal receives a request for establishing a first part of a connection for terminal-to-terminal relay communication via the first hop on the first hop terminating at the relay terminal (S110). The request includes a first local identifier. For example, the request can be a DCA command (for alternative 1) or a DCR command (for alternative 2).

[0305] If the relay terminal receives the request (S110=Yes), the means 120 for determining determines the second local identifier so that the second local identifier is unique among all local identifiers associated with the identifier of the second hop in the mapping table (S120). The second hop terminates at the relay terminal.

[0306] The storing means 130 stores the first mapping information mapped to the second mapping information in the mapping table (S130). The first mapping information includes an identifier of the first hop associated with the first local identifier received in S110. The second mapping information includes an identifier of the second hop associated with the second local identifier determined in S120.

[0307] The means 140 for indicating indicates that a second part of the connection for the terminal-to-terminal relay communication is established via the corresponding second hop (S140). The indication of S140 includes a second local identifier.

[0308] As described above, S110 to S140 may be repeated for creating a corresponding connection for each or one or more U2U relay communications between a corresponding SRC UE and a corresponding DST UE. If one or more of these connections are established, they may be used for data transmission. Data transmission may be in the direction from the SRC UE (=TX UE) to the DST UE (=RX UE) or in the direction from the DST UE (=TX UE) to the SRC UE (=RX UE). That is, the terms SRC UE and DST UE may only be related to the creation of a connection, and the terms TX UE and RX UE may only be related to the transmission of data on the connection. S150 to S170 are related to data transmission of one of the U2U relay communications for which a connection is created.

[0309] The means 150 for supervising supervises whether the relay terminal receives data of the terminal-to-terminal relay communication including the third local identifier at the ingress hop terminating at the relay terminal (S150).

[0310] If the relay terminal receives data of the terminal-to-terminal relay communication including the third local identifier on the ingress hop (S150=Yes), the component 160 for identifying identifies the fourth mapping information based on the third mapping information (S160). The third mapping information includes an identifier of the ingress hop associated with the third local identifier. The fourth mapping information includes an identifier of the egress hop associated with the fourth local identifier. The fourth mapping information is mapped to the third mapping information in the mapping table. The egress hop terminates at the relay terminal.

[0311] The forwarding component 170 forwards the data of the terminal-to-terminal relay communication including the fourth local identifier on the egress hop identified in S160 in the direct U2U communication (S170).

[0312] Fig.11 An apparatus according to an exemplary embodiment of the present invention is shown. The apparatus may be a terminal, such as a UE (particularly an endpoint UE, such as a SRC UE or a DST UE for U2U relay communication), or an element thereof. Fig.12 A method according to an exemplary embodiment of the present invention is shown. Fig.11 The device can perform Fig.12 method, but not limited to this method. Fig.12 The method can be Fig.11 The present invention is performed by a device, but is not limited to being performed by the device.

[0313] The apparatus comprises a component 210 for determining, a component 220 for storing, a component 230 for indicating, a component 240 for supervising, a component 250 for identifying, and a component 260 for forwarding. The component 210 for determining, the component 220 for storing, the component 230 for indicating, the component 240 for supervising, the component 250 for identifying, and the component 260 for forwarding may be a determining component, a storing component, an indicating component, a supervising component, an identifying component, and a forwarding component, respectively. The component 210 for determining, the component 220 for storing, the component 230 for indicating, the component 240 for supervising, the component 250 for identifying, and the component 260 for forwarding may be a determiner, a storage device, an indicator, a supervisor, an identifier, and a forwarder, respectively. The component 210 for determining, the component 220 for storing, the component 230 for indicating, the component 240 for supervising, the component 250 for identifying, and the component 260 for forwarding may be a determining processor, a storing processor, an indicating processor, a supervising processor, an identifying processor, and a forwarding processor, respectively.

[0314] S210 to S230 are performed for each U2U relay communication ("terminal to terminal relay communication") to create a connection for the U2U relay communication. Each U2U relay communication in the U2U relay communication is defined by a corresponding source UE and a corresponding destination UE. S210 to S230 are described below for one U2U relay communication in the U2U relay communication.

[0315] The means 210 for determining determines the first local identifier such that the first local identifier is unique among all local identifiers associated with the identifier of the first hop in the mapping table (S210).The first hop terminates at a first endpoint terminal.

[0316] The storage component 220 stores first mapping information mapped to the identifier of the terminal-to-terminal relay communication in the mapping table (S220). The first mapping information includes an identifier of the first hop associated with the first local identifier.

[0317] The means 230 for indicating indicates establishing a first part of a connection for a terminal-to-terminal relay communication via a corresponding first hop (S230). The indication of S230 includes a first local identifier.

[0318] As described above, S210 to S230 may be repeated for creating a corresponding connection for each or one or more U2U relay communications between a corresponding first endpoint UE (SRC UE or DST UE) and a second endpoint UE (DST UE or SRC UE). If one or more of these connections are established, they may be used for data transmission. Data transmission may be in the direction from the SRC UE (=TX UE) to the DST UE (=RX UE) or in the direction from the DST UE (=TX UE) to the SRC UE (=RXUE). That is, the terms SRC UE and DST UE may only relate to the creation of a connection, and the terms TX UE and RX UE may only relate to the transmission of data on the connection. S240 to S260 relate to data transmission of one of the U2U relay communications for which the connection is created.

[0319] The means 240 for supervising supervises whether the first endpoint terminal (SRC UE or DST UE) intends to transmit data of the terminal-to-terminal relay communication to the second endpoint terminal (DST UE or SRC UE) of the terminal-to-terminal relay communication (S240).

[0320] If the first endpoint terminal intends to send data of the terminal-to-terminal relay communication (S240=Yes), the component 250 for identifying identifies the identified mapping information based on the identifier of the terminal-to-terminal relay communication (S250). The identified mapping information includes an identifier of the egress hop associated with the identified local identifier. The identified mapping information is mapped to the terminal-to-terminal relay communication in a mapping table. The egress hop terminates at the first endpoint terminal.

[0321] The means 250 for transmitting transmits the data of the terminal-to-terminal relay communication including the identified local identifier on the egress hop identified in S240 in the direct U2U communication (S250).

[0322] Fig.13 An apparatus according to an example embodiment of the present invention is shown. The apparatus comprises at least one processor 810, at least one memory 820 storing instructions, which, when executed by at least one processor 810, causes the apparatus to perform at least a method according to at least one of the following figures and the related description: Fig.10 or Fig.12 .

[0323] Some example embodiments are explained with respect to 5G networks. However, the present invention is not limited to 5G. The present invention may also be used in other communication networks, for example, in previous or upcoming generations of 3GPP networks (such as 4G, 6G or 7G, etc.). The present invention may also be used in non-3GPP communication networks that provide U2U relay communication services.

[0324] A piece of information may be sent from one entity to another in one or more messages. Each of these messages may include another (different) piece of information.

[0325] The names of network elements, network functions, protocols and methods are based on current standards. In other versions or other technologies, the names of these network elements and / or network functions and / or protocols and / or methods may be different, as long as they provide corresponding functions. The same applies to terminals accordingly.

[0326] Unless otherwise stated or otherwise clear from the context, a statement that two entities are different means that they perform different functions. This does not necessarily mean that they are based on different hardware. That is, each of the entities described in this specification can be based on different hardware, or some or all of the entities can be based on the same hardware. This does not necessarily mean that they are based on different software. That is, each of the entities described in this specification can be based on different software, or some or all of the entities can be based on the same software. Each of the entities described in this specification can be deployed in the cloud.

[0327] Based on the above description, it should be clear that the exemplary embodiments of the present invention provide, for example, a terminal (such as a UE or an MTC device) or a component thereof, an apparatus embodying the terminal or its components, a method for controlling and / or operating the terminal or its components, (multiple) computer programs for controlling and / or operating the terminal and / or its components, and a medium that carries such (multiple) computer programs and forms (multiple) computer program products.

[0328] As non-limiting examples, implementation of any of the blocks, devices, systems, techniques, or methods described above includes implementation as hardware, software, firmware, dedicated circuits or logic, general purpose hardware or controllers or other computing devices, or some combination thereof. Each of the entities described in this specification may be embodied in the cloud.

[0329] It should be understood that what has been described above is what is currently considered to be the preferred exemplary embodiment of the present invention. However, it should be noted that the description of the preferred exemplary embodiment is given by way of example only and that various modifications may be made without departing from the scope of the present invention as defined in the appended claims.

[0330] Unless otherwise specified, the terms "first X" and "second X" include options: "first X" is the same as "second X"; and "first X" is different from "second X". As used herein, "at least one of: " and "at least one of " and similar expressions (wherein a list of two or more elements is connected by "and" or "or") mean at least any one of the elements, or at least any two or more of the elements, or at least all of the elements.

Claims

1. A device comprising: one or more processors, and a memory storing instructions that, when executed by the one or more processors, cause the apparatus to perform: For each of the one or more terminal-to-terminal relay communications between the corresponding source terminal and the corresponding destination terminal: - monitoring whether a relay terminal receives, at a respective first hop terminating at said relay terminal, a request to establish a first part of a connection for a respective said terminal-to-terminal relay communication via said respective first hop, wherein said request comprises a respective first local identifier; - if the relay terminal receives the request, determining a corresponding second local identifier such that the corresponding second local identifier is unique among all local identifiers associated with an identifier of a corresponding second hop terminating at the relay terminal in a mapping table; - storing, in the mapping table, corresponding first mapping information mapped to corresponding second mapping information, wherein the corresponding first mapping information comprises the identifier of the corresponding first hop associated with the corresponding first local identifier, and the corresponding second mapping information comprises the identifier of the corresponding second hop associated with the corresponding second local identifier; as well as - instructing establishment of a second part of said connection for a corresponding said device-to-device relay communication via said corresponding second hop, wherein said indication comprises said corresponding second local identifier; supervising whether the relay terminal receives data of one of the one or more terminal-to-terminal relay communications including a third local identifier at an ingress hop terminating at the relay terminal; if the relay terminal receives the data of the one of the one or more terminal-to-terminal relay communications including the third local identifier at the ingress hop, identifying fourth mapping information including an identifier of an egress hop associated with a fourth local identifier based on third mapping information including an identifier of the ingress hop associated with the third local identifier, wherein the fourth mapping information is mapped to the third mapping information in the mapping table, and the egress hop terminates at the relay terminal; as well as The data of the one of the one or more terminal-to-terminal relay communications including the fourth local identifier is forwarded on the egress hop.

2. The apparatus of claim 1 , wherein the instructions, when executed by the one or more processors, further cause the apparatus to perform: monitoring whether the relay terminal receives a first command to form the first portion of the connection for a first terminal-to-terminal relay communication of the one or more terminal-to-terminal relay communications via a fifth hop different from the second hop after the first portion of the connection for the first terminal-to-terminal relay communication is formed via the first hop, wherein the first command includes a fifth local identifier and the fifth hop terminates at the relay terminal; The first mapping information for the first device-to-device relay communication is replaced in the mapping table with fifth mapping information, wherein the fifth mapping information includes an identifier of the fifth hop associated with the fifth local identifier.

3. The apparatus according to any one of claims 1 to 2, wherein the instructions, when executed by the one or more processors, further cause the apparatus to execute: monitoring whether the relay terminal receives a second command to form the second portion of the connection for a second terminal-to-terminal relay communication of the one or more terminal-to-terminal relay communications via a sixth hop different from the second hop after the second portion of the connection for the second terminal-to-terminal relay communication is formed via the second hop, wherein the sixth hop terminates at the relay terminal; If the relay terminal receives the second command, determining a sixth local identifier such that the sixth local identifier is unique among all local identifiers associated with the identifier of the sixth hop in the mapping table; replacing the second mapping information for the second device-to-device relay communication with sixth mapping information in the mapping table, wherein the sixth mapping information includes the identifier of the sixth hop associated with the sixth local identifier; and Instructing establishment of the second portion of the connection for the second device-to-device relay communication via the corresponding sixth hop, wherein the instruction includes the sixth local identifier.

4. The apparatus according to any one of claims 1 to 3, wherein for at least one of the one or more terminal-to-terminal relay communications: the request to establish the first portion of the connection for the corresponding device-to-device relay communication via the corresponding first hop comprises a first direct communication accept command; and The indication to establish the second portion of the connection for the corresponding device-to-device relay communication via the corresponding second hop comprises a second direct communication accept command.

5. The apparatus according to any one of claims 1 to 4, wherein for at least one of the one or more terminal-to-terminal relay communications: the request to establish the first portion of the connection for the corresponding device-to-device relay communication via the corresponding first hop comprises a first direct communication request command; and The indication to establish the second portion of the connection for the corresponding device-to-device relay communication via the corresponding second hop comprises a second direct communication request command.

6. The apparatus according to any one of claims 1 to 5, wherein for each of the one or more terminal-to-terminal relay communications, at least one of the following identifiers is a layer 2 identifier of a corresponding neighboring terminal, or each of the following identifiers is a layer 2 identifier of the corresponding neighboring terminal: - said identifier of said corresponding first hop, - said identifier of said corresponding second hop, - said identifier of said corresponding third hop, or - said identifier of said corresponding fourth hop; The corresponding neighboring terminal is connected to the relay terminal via a corresponding one of the corresponding first hop, the corresponding second hop, the corresponding third hop, or the corresponding fourth hop.

7. The apparatus according to any one of claims 1 to 6, wherein for each of the one or more terminal-to-terminal relay communications, at least one of the following: the corresponding first local identifier is shorter than the layer 2 identifier; or The corresponding second local identifier is shorter than the layer 2 identifier.

8. The apparatus according to any one of claims 1 to 7, wherein the instructions, when executed by the one or more processors, further cause the apparatus to perform, for each of the one or more terminal-to-terminal relay communications: The determining of the corresponding second local identifier is performed without regard to at least one of the following identifiers or without regard to any of the following identifiers: - an identifier of the corresponding source terminal, - an identifier of the corresponding destination terminal, - said identifier of said corresponding first hop, or - said corresponding first local identifier.

9. The apparatus according to any one of claims 1 to 8, wherein the data comprises a protocol data unit of a sidelink relay adaptation layer for the terminal-to-terminal relay communication, and a header of the protocol data unit comprises the third local identifier.

10. An apparatus comprising: one or more processors, and a memory storing instructions that, when executed by the one or more processors, cause the apparatus to perform: For each of the one or more terminal-to-terminal relay communications between the first endpoint terminal and the corresponding second endpoint terminal: - determining a respective first local identifier such that the respective first local identifier is unique among all local identifiers associated in a mapping table with an identifier of a respective first hop terminating at the first endpoint terminal; - storing in the mapping table corresponding first mapping information mapped to the corresponding identifier of the terminal-to-terminal relay communication, wherein the corresponding first mapping information comprises the identifier of the corresponding first hop associated with the corresponding first local identifier; as well as - an indication of establishing a first part of a connection for a corresponding said terminal-to-terminal relay communication via said corresponding first hop, wherein said indication comprises said corresponding first local identifier; supervising whether the first endpoint terminal intends to send data of one of the one or more terminal-to-terminal relay communications to the corresponding second endpoint terminal; If the first endpoint terminal intends to send the data of the one of the one or more terminal-to-terminal relay communications, identifying the identified mapping information based on the identifier of the one of the one or more terminal-to-terminal relay communications, the identified mapping information comprising an identifier of an egress hop associated with the identified local identifier, wherein the identified mapping information is mapped to the identifier of the one of the one or more terminal-to-terminal relay communications in the mapping table, and the egress hop terminates at the first endpoint terminal; as well as The data of the one of the one or more terminal-to-terminal relay communications including the identified local identifier is transmitted over the egress hop.

11. The apparatus of claim 10, wherein the instructions, when executed by the one or more processors, further cause the apparatus to perform: monitoring whether the first endpoint terminal intends to form the first portion of the connection for a first terminal-to-terminal relay communication of the one or more terminal-to-terminal relay communications via a second hop different from the first hop after the first portion of the connection for the first terminal-to-terminal relay communication is formed via the first hop, wherein the second hop terminates at the first endpoint terminal; if the first endpoint terminal intends to form the first portion of the connection for the first terminal-to-terminal relay communication via the second hop, determining a second local identifier such that the second local identifier is unique among all local identifiers associated with an identifier of the second hop in the mapping table; replacing the first mapping information with second mapping information in the mapping table, wherein the second mapping information includes the identifier of the second hop associated with the second local identifier; as well as Instructing establishment of the first portion of the connection for the first device-to-device relay communication via the second hop, wherein the instruction includes the second local identifier.

12. The apparatus according to any one of claims 10 to 11, wherein for each of the one or more terminal-to-terminal relay communications, at least one of the following identifiers is a layer 2 identifier of a corresponding neighboring terminal, or each of the following identifiers is a layer 2 identifier of the corresponding neighboring terminal: - said identifier of said corresponding first hop, or - said identifier of said egress hop; The corresponding first hop or the exit hop is terminated at the corresponding adjacent terminal and the first endpoint terminal.

13. The apparatus according to any one of claims 10 to 12, wherein for each of the one or more terminal-to-terminal relay communications: The corresponding first local identifier is shorter than the layer 2 identifier.

14. The apparatus according to any one of claims 10 to 13, wherein the instructions, when executed by the one or more processors, further cause the apparatus to perform, for each of the one or more device-to-device relay communications: The determining of the corresponding first local identifier is without considering at least one of the following identifiers or without considering any of the following identifiers: - an identifier of said first endpoint terminal, - an identifier of the corresponding second endpoint terminal, or - said identifier of said corresponding first hop.

15. The apparatus according to any one of claims 10 to 14, wherein for at least one of the one or more terminal-to-terminal relay communications: The first endpoint terminal is a source terminal of the corresponding terminal-to-terminal relay communication; and The indication to establish the first portion of the connection for the corresponding device-to-device relay communication via the corresponding first hop comprises a direct communication request command.

16. The apparatus according to any one of claims 10 to 15, wherein for at least one of the one or more terminal-to-terminal relay communications: The first endpoint terminal is a destination terminal of the corresponding terminal-to-terminal relay communication; and The indication of establishing the first portion of the connection for the respective device-to-device relay communication via the respective first hop comprises a direct communication accept command.

17. A method comprising: For each of the one or more terminal-to-terminal relay communications between the corresponding source terminal and the corresponding destination terminal: - monitoring whether a relay terminal receives, at a respective first hop terminating at said relay terminal, a request to establish a first part of a connection for a respective said terminal-to-terminal relay communication via said respective first hop, wherein said request comprises a respective first local identifier; - if the relay terminal receives the request, determining a corresponding second local identifier such that the corresponding second local identifier is unique among all local identifiers associated with an identifier of a corresponding second hop terminating at the relay terminal in a mapping table; - storing, in the mapping table, corresponding first mapping information mapped to corresponding second mapping information, wherein the corresponding first mapping information comprises the identifier of the corresponding first hop associated with the corresponding first local identifier, and the corresponding second mapping information comprises the identifier of the corresponding second hop associated with the corresponding second local identifier; as well as - instructing establishment of a second part of said connection for a corresponding said device-to-device relay communication via said corresponding second hop, wherein said indication comprises said corresponding second local identifier; supervising whether the relay terminal receives data of one of the one or more terminal-to-terminal relay communications including a third local identifier at an ingress hop terminating at the relay terminal; if the relay terminal receives the data of the one of the one or more terminal-to-terminal relay communications including the third local identifier at the ingress hop, identifying fourth mapping information including an identifier of an egress hop associated with a fourth local identifier based on third mapping information including an identifier of the ingress hop associated with the third local identifier, wherein the fourth mapping information is mapped to the third mapping information in the mapping table, and the egress hop terminates at the relay terminal; as well as The data of the one of the one or more terminal-to-terminal relay communications including the fourth local identifier is forwarded on the egress hop.

18. A method comprising: For each of the one or more terminal-to-terminal relay communications between the first endpoint terminal and the corresponding second endpoint terminal: - determining a respective first local identifier such that the respective first local identifier is unique among all local identifiers associated in a mapping table with an identifier of a respective first hop terminating at the first endpoint terminal; - storing in the mapping table corresponding first mapping information mapped to the corresponding identifier of the terminal-to-terminal relay communication, wherein the corresponding first mapping information comprises the identifier of the corresponding first hop associated with the corresponding first local identifier; as well as - an indication of establishing a first part of a connection for a corresponding said terminal-to-terminal relay communication via said corresponding first hop, wherein said indication comprises said corresponding first local identifier; supervising whether the first endpoint terminal intends to send data of one of the one or more terminal-to-terminal relay communications to the corresponding second endpoint terminal; If the first endpoint terminal intends to send the data of the one of the one or more terminal-to-terminal relay communications, identifying the identified mapping information based on the identifier of the one of the one or more terminal-to-terminal relay communications, the identified mapping information comprising an identifier of an egress hop associated with the identified local identifier, wherein the identified mapping information is mapped to the identifier of the one of the one or more terminal-to-terminal relay communications in the mapping table, and the egress hop terminates at the first endpoint terminal; as well as The data of the one of the one or more terminal-to-terminal relay communications including the identified local identifier is transmitted over the egress hop.

19. A computer program product comprising a set of instructions which, when executed on a device, are configured to cause the device to perform the method according to any one of claims 17 and 18.

Images