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Content for  TS 23.304  Word version:  19.1.0

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6.4.3 Unicast mode 5G ProSe Direct Communication  6.4.3.1 Layer-2 link establishment over PC5 reference point  6.4.3.2 Link identifier update for a unicast link  6.4.3.3 Layer-2 link release over PC5 reference point  6.4.3.4 Layer-2 link modification for a unicast link  6.4.3.5 Layer-2 link maintenance over PC5 reference point  6.4.3.6 Layer-2 link management over PC5 reference point for 5G ProSe UE-to-Network Relay  6.4.3.7 Layer-2 link management over PC5 reference point for 5G ProSe UE-to-UE Relay  6.4.3.7.1 Common part for Layer-2 link management over PC5 reference point for 5G ProSe UE-to-UE Relay  6.4.3.7.2 Layer-2 link management over PC5 reference point for 5G ProSe Layer-2 UE-to-UE Relay  6.4.3.7.3 Layer-2 link management over PC5 reference point for 5G ProSe Layer-3 UE-to-UE Relay  6.4.3.7.4 Layer-2 link management over PC5 reference point for 5G ProSe UE-to-UE Relay Communication with integrated Discovery  6.4.3.8 Layer-2 link management over PC5 reference point for 5G ProSe multi-hop UE-to-Network Relay  6.4.3.8.1 Layer-2 Link establishment and management (based on Model A discovery)  6.4.3.8.2 IP address/prefix management for 5G ProSe Layer-3 Multi-hop UE-to-Network Relay  6.4.3.8.3 Relay reselection and mobility support  6.4.3.9 Layer-2 link management over PC5 reference point for Multi-hop 5G ProSe UE-to-Network Relay (based on Model B Discovery)  6.4.3.10 Layer-2 link management for 5G ProSe Layer-3 Multi-hop UE-to-UE Relay  6.4.3.10.1 Layer-2 Link establishment and management for IP PDU type  6.4.3.10.2 Layer-2 link establishement and management over PC5 reference point for non-IP PDU type 
...

 

6.4.3  Unicast mode 5G ProSe Direct Communication  p. 118

6.4.3.1  Layer-2 link establishment over PC5 reference point  p. 118

To perform unicast mode of ProSe Direct communication over PC5 reference point, the UE is configured with the related information as described in clause 5.1.3.
Figure 6.4.3.1-1 shows the layer-2 link establishment procedure for the unicast mode of ProSe Direct communication over PC5 reference point.
Copy of original 3GPP image for 3GPP TS 23.304, Fig. 6.4.3.1-1: Layer-2 link establishment procedure
Figure 6.4.3.1-1: Layer-2 link establishment procedure
(⇒ copy of original 3GPP image)
Up
Step 1.
The UE(s) determine the destination Layer-2 ID for signalling reception for PC5 unicast link establishment as specified in clause 5.8.2.4.
Step 2.
The ProSe application layer in UE-1 provides application information for PC5 unicast communication. The application information includes the ProSe Service Info, UE's Application Layer ID. The target UE's Application Layer ID may be included in the application information.
The ProSe application layer in UE-1 may provide ProSe Application Requirements for this unicast communication. UE-1 determines the PC5 QoS parameters and PFI as specified in clause 5.6.1.
If UE-1 decides to reuse the existing PC5 unicast link as specified in clause 5.3.4, the UE triggers the Layer-2 link modification procedure as specified in clause 6.4.3.4.
Step 3.
UE-1 sends a Direct Communication Request message to initiate the unicast layer-2 link establishment procedure. The Direct Communication Request message includes:
  • Source User Info: the initiating UE's Application Layer ID (i.e. UE-1's Application Layer ID).
  • If the ProSe application layer provided the target UE's Application Layer ID in step 2, the following information is included:
    • Target User Info: the target UE's Application Layer ID (i.e. UE-2's Application Layer ID).
  • ProSe Service Info: the information about the ProSe identifier(s) requesting Layer-2 link establishment.
  • Security Information: the information for the establishment of security.
The source Layer-2 ID and destination Layer-2 ID used to send the Direct Communication Request message are determined as specified in clauses 5.8.2.1 and 5.8.2.4. The destination Layer-2 ID may be broadcast or unicast Layer-2 ID. When unicast Layer-2 ID is used, the Target User Info shall be included in the Direct Communication Request message.
UE-1 sends the Direct Communication Request message via PC5 broadcast or unicast using the source Layer-2 ID and the destination Layer-2 ID.
A default PC5 DRX configuration may be used for transmitting and receiving of this message (see TS 38.300).
Step 4.
Security with UE-1 is established as below:
Step 4a.
If the Target User Info is included in the Direct Communication Request message, the target UE, i.e. UE-2, responds by establishing the security with UE-1.
Step 4b.
If the Target User Info is not included in the Direct Communication Request message, the UEs that are interested in using the announced ProSe Service(s) over a PC5 unicast link with UE-1 responds by establishing the security with UE-1.
When the security protection is enabled, UE-1 sends the following information to the target UE:
  • If IP communication is used:
    • IP Address Configuration: For IP communication, IP address configuration is required for this link and indicates one of the following values:
      • "DHCPv4 server" if only IPv4 address allocation mechanism is supported by the initiating UE, i.e., acting as a DHCPv4 server; or
      • "IPv6 Router" if only IPv6 address allocation mechanism is supported by the initiating UE, i.e., acting as an IPv6 Router; or
      • "DHCPv4 server & IPv6 Router" if both IPv4 and IPv6 address allocation mechanism are supported by the initiating UE; or
      • "address allocation not supported" if neither IPv4 nor IPv6 address allocation mechanism is supported by the initiating UE.
    • Link-Local IPv6 Address: a link-local IPv6 address formed locally based on RFC 4862 if UE-1 does not support the IPv6 IP address allocation mechanism, i.e. the IP Address Configuration indicates "address allocation not supported".
  • QoS Info: the information about PC5 QoS Flow(s). For each PC5 QoS Flow, the PFI and the corresponding PC5 QoS parameters (i.e. PQI and conditionally other parameters such as MFBR/GFBR, etc.) and optionally the associated ProSe identifier(s).
  • Optional PC5 QoS Rule(s).
The source Layer-2 ID used for the security establishment procedure is determined as specified in clauses 5.8.2.1 and 5.8.2.4. The destination Layer-2 ID is set to the source Layer-2 ID of the received Direct Communication Request message.
Upon receiving the security establishment procedure messages, UE-1 obtains the peer UE's Layer-2 ID for future communication, for signalling and data traffic for this unicast link.
Step 5.
A Direct Communication Accept message is sent to UE-1 by the target UE(s) that has successfully established security with UE-1:
Step 5a.
(UE oriented Layer-2 link establishment) If the Target User Info is included in the Direct Communication Request message, the target UE, i.e. UE-2 responds with a Direct Communication Accept message if the Application Layer ID for UE-2 matches.
Step 5b.
(ProSe Service oriented Layer-2 link establishment) If the Target User Info is not included in the Direct Communication Request message, the UEs that are interested in using the announced ProSe Service(s) respond to the request by sending a Direct Communication Accept message (UE-2 and UE-4 in Figure 6.4.3.1-1).
The Direct Communication Accept message includes:
  • Source User Info: Application Layer ID of the UE sending the Direct Communication Accept message.
  • QoS Info: the information about PC5 QoS Flow(s). For each PC5 QoS Flow, the PFI and the corresponding PC5 QoS parameters requested by UE-1 (i.e. PQI and conditionally other parameters such as MFBR/GFBR, etc.) and optionally the associated ProSe identifiers(s).
  • Optional PC5 QoS Rule(s).
  • If IP communication is used:
    • IP Address Configuration: For IP communication, IP address configuration is required for this link and indicates one of the following values:
      • "DHCPv4 server" if only IPv4 address allocation mechanism is supported by the target UE, i.e., acting as a DHCPv4 server; or
      • "IPv6 Router" if only IPv6 address allocation mechanism is supported by the target UE, i.e., acting as an IPv6 Router; or
      • "DHCPv4 server & IPv6 Router" if both IPv4 and IPv6 address allocation mechanism are supported by the target UE; or
      • "address allocation not supported" if neither IPv4 nor IPv6 address allocation mechanism is supported by the target UE.
    • Link-Local IPv6 Address: a link-local IPv6 address formed locally based on RFC 4862 if the target UE does not support the IPv6 IP address allocation mechanism, i.e. the IP Address Configuration indicates "address allocation not supported" and UE-1 included a link-local IPv6 address in the security establishment in step 4. The target UE shall include a non-conflicting link-local IPv6 address.
If both UEs (i.e. the initiating UE and the target UE) are selected to use link-local IPv6 address, they shall disable the duplicate address detection defined in RFC 4862.
The ProSe layer of the UE that established PC5 unicast link passes the PC5 Link Identifier assigned for the unicast link and the PC5 unicast link related information down to the AS layer. The PC5 unicast link related information includes Layer-2 ID information (i.e. source Layer-2 ID and destination Layer-2 ID). This enables the AS layer to maintain the PC5 Link Identifier together with the PC5 unicast link related information.
Two UEs may negotiate the PC5 DRX configuration in the AS layer and the PC5 DRX parameter values can be configured per pair of source and destination Layer-2 IDs in the AS layer.
Step 6.
ProSe data is transmitted over the established unicast link as below:
The PC5 Link Identifier and PFI are provided to the AS layer, together with the ProSe data.
Optionally in addition, the Layer-2 ID information (i.e. source Layer-2 ID and destination Layer-2 ID) is provided to the AS layer.
UE-1 sends the ProSe data using the source Layer-2 ID (i.e. UE-1's Layer-2 ID for this unicast link) and the destination Layer-2 ID (i.e. the peer UE's Layer-2 ID for this unicast link).
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6.4.3.2  Link identifier update for a unicast link  p. 122

Figure 6.4.3.2-1 shows the link identifier update procedure for a unicast link. When privacy requirements are configured for a ProSe Identifier associated with the unicast link, identifiers used for the unicast mode of 5G ProSe communication over PC5 reference point (e.g. Application Layer ID, Source Layer-2 ID and IP address/prefix) shall be changed over time as specified in clauses 5.8.2.1 and 5.8.2.4. A UE may decide to change the identifiers for other reasons, e.g. application layer requirement. This procedure is used to update and exchange new identifiers between the source and the peer UEs for a unicast link before using the new identifiers, to prevent service interruptions. When there are privacy requirements as indicated above, this procedure is executed over a security protected unicast link.
If a UE has multiple unicast links using the same Application Layer IDs or Layer-2 IDs, the UE needs to perform the link identifier update procedure over each of the unicast links.
Copy of original 3GPP image for 3GPP TS 23.304, Fig. 6.4.3.2-1: Link identifier update procedure
Figure 6.4.3.2-1: Link identifier update procedure
(⇒ copy of original 3GPP image)
Up
Step 0.
UE-1 and UE-2 have a unicast link established as described in clause 6.4.3.1.
Step 1.
UE-1 decides to change its identifier(s), e.g. due to the Application Layer ID change or upon expiry of a timer. UE-1 generates its new Layer-2 ID and sends a Link Identifier Update Request message to UE-2 using the old identifiers.
The Link Identifier Update Request message includes the new identifier(s) to use (including the new Layer-2 ID, Security Information, optionally the new Application Layer ID and optionally new IP address/prefix if IP communication is used). The new identifier(s) shall be cyphered to protect privacy if security is configured for the unicast link. After sending the Link Identifier Update Request message, if the UE-1 has data to send, UE-1 keeps sending data traffic to UE-2 with the old identifiers until UE-1 sends the Link Identifier Update Ack message to UE-2.
Step 2.
Upon reception of the Link Identifier Update Request message, UE-2 changes its identifier(s). UE-2 responds with a Link Identifier Update Response message which includes the new identifier(s) to use (including the new Layer-2 ID, Security Information, optionally the new Application Layer ID and optionally a new IP address/prefix if IP communication is used). The new identifier(s) shall be cyphered to protect privacy if security is configured for the unicast link. The Link Identifier Update Response message is sent using the old identifiers. UE-2 continues to receive traffic with the old Layer-2 ID from UE-1 until UE-2 receives traffic with the new Layer-2 ID from UE-1. After sending the Link Identifier Update Response message, UE-2 keeps sending data traffic to UE-1 with the old identifier, if UE-2 has data to send, until UE-2 receives the Link Identifier Update Ack message from UE-1.
Step 3.
Upon reception of the Link Identifier Update Response message, UE-1 responds with a Link Identifier Update Ack message. The Link Identifier Update Ack message includes the new identifier(s) from UE-2, as received on the Link Identifier Update Response message. The Link Identifier Update Ack message is sent using the old identifiers. UE-1 continues to receive traffic with the old Layer-2 ID from UE-2 until UE-1 receives traffic with the new Layer-2 ID from UE-2.
Step 4.
The ProSe layer of UE-1 passes the PC5 Link Identifier for the unicast link and the updated Layer-2 IDs (i.e. new Layer-2 ID for UE-1 for the source and new Layer-2 ID of UE-2 for the destination) down to the AS layer. This enables the AS layer to update the provided Layer-2 IDs for the unicast link.
UE-1 starts using its new identifiers and UE-2's new identifiers for this unicast link.
Step 5.
Upon reception of the Link Identifier Update Ack message, the ProSe layer of UE-2 passes the PC5 Link Identifier for the unicast link and the updated Layer-2 IDs (i.e. new Layer-2 ID of UE-2 for the source and new Layer-2 ID for UE-1 for the destination) down to the AS layer. This enables the AS layer to update the provided Layer-2 IDs for the unicast link.
UE-2 starts using its new identifiers and UE-1's new identifiers for this unicast link.
Up

6.4.3.3  Layer-2 link release over PC5 reference point  p. 123

Figure 6.4.3.3-1 shows the layer-2 link release procedure over PC5 reference point.
Copy of original 3GPP image for 3GPP TS 23.304, Fig. 6.4.3.3-1: Layer-2 link release procedure
Figure 6.4.3.3-1: Layer-2 link release procedure
(⇒ copy of original 3GPP image)
Up
Step 0.
UE-1 and UE-2 have a unicast link established as described in clause 6.4.3.1.
Step 1.
UE-1 sends a Disconnect Request message to UE-2 in order to release the layer-2 link and deletes all context data associated with the layer-2 link. The Disconnect Request message includes Security Information.
Step 2.
Upon reception of the Disconnect Request message, UE-2 shall respond with a Disconnect Response message and deletes all context data associated with the layer-2 link. The Disconnect Response message includes Security Information.
The ProSe layer of each UE informs the AS layer that the unicast link has been released. The ProSe layer uses PC5 Link Identifier to indicate the released unicast link. This enables the AS layer to delete the context related to the released unicast link.
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6.4.3.4  Layer-2 link modification for a unicast link  p. 124

Figure 6.4.3.4-1 shows the layer-2 link modification procedure for a unicast link. This procedure is used to:
  • add new PC5 QoS Flow(s) in the existing PC5 unicast link.
    • This covers the case for adding new PC5 QoS Flow(s) to the existing ProSe service(s) as well as the case for adding new PC5 QoS Flow(s) to new ProSe service(s).
  • modify existing PC5 QoS Flow(s) in the existing PC5 unicast link.
    • This covers the case for modifying the PC5 QoS parameters for existing PC5 QoS Flow(s).
    • This also covers the case for removing the associated ProSe service(s) from existing PC5 QoS Flow(s) as well as the case for associating new ProSe service(s) with existing PC5 QoS Flow(s).
  • remove existing PC5 QoS Flow(s) in the existing PC5 unicast link.
Copy of original 3GPP image for 3GPP TS 23.304, Fig. 6.4.3.4-1: Layer-2 link modification procedure
Figure 6.4.3.4-1: Layer-2 link modification procedure
(⇒ copy of original 3GPP image)
Up
Step 0.
UE-1 and UE-2 have a unicast link established as described in clause 6.4.3.1.
Step 1.
The ProSe application layer in UE-1 provides application information for PC5 unicast communication. The application information includes the ProSe Service Info and the initiating UE's Application Layer ID. The target UE's Application Layer ID may be included in the application information. If UE-1 decides to reuse the existing PC5 unicast link as specified in clause 5.3.4, so decides to modify the unicast link established with UE-2, UE-1 sends a Link Modification Request to UE-2.
The Link Modification Request message includes:
  1. To add new PC5 QoS Flow(s) in the existing PC5 unicast link:
    • QoS Info: the information about PC5 QoS Flow(s) to be added. For each PC5 QoS Flow, the PFI, the corresponding PC5 QoS parameters (i.e. PQI and conditionally other parameters such as MFBR/GFBR, etc.) and optionally the associated ProSe identifier(s).
    • Optional PC5 QoS Rule(s).
  2. To modify PC5 QoS Flow(s) in the existing PC5 unicast link:
    • QoS Info: the information about PC5 QoS Flow(s) to be modified. For each PC5 QoS Flow, the PFI, the corresponding PC5 QoS parameters (i.e. PQI and conditionally other parameters such as MFBR/GFBR, etc.) and optionally the associated ProSe identifier(s).
    • Optional PC5 QoS Rule(s).
  3. To remove PC5 QoS Flow(s) in the existing PC5 unicast link:
    • PFIs.
Step 2.
UE-2 responds with a Link Modification Accept message.
The Link Modification Accept message includes:
  • For case a) and case b) described in step 1:
    • QoS Info: the information about PC5 QoS Flow(s) requested by UE-1. For each PC5 QoS Flow, the PFI, the corresponding PC5 QoS parameters (i.e. PQI and conditionally other parameters such as MFBR/GFBR, etc.) and optionally the associated ProSe identifier(s).
    • Optional PC5 QoS Rule(s).
The ProSe layer of each UE provides information about the unicast link modification to the AS layer. This enables the AS layer to update the context related to the modified unicast link.
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6.4.3.5  Layer-2 link maintenance over PC5 reference point  p. 125

The PC5 Signalling Protocol shall support keep-alive functionality that is used to detect if a particular PC5 unicast link is still valid. Either side of the PC5 unicast link can initiate the layer-2 link maintenance procedure (i.e. keep-alive procedure), based on for example triggers from the AS layer or internal timers. The UEs shall minimize the keep-alive signalling, e.g. cancel the procedure if data are successfully received over the PC5 unicast link.
Copy of original 3GPP image for 3GPP TS 23.304, Fig. 6.4.3.5-1: Layer-2 link maintenance procedure
Figure 6.4.3.5-1: Layer-2 link maintenance procedure
(⇒ copy of original 3GPP image)
Up
Step 0.
UE-1 and UE-2 have a unicast link established as described in clause 6.4.3.1.
Step 1.
Based on trigger conditions, UE-1 sends a Keep-alive message to UE-2 in order to determine the status of the PC5 unicast link.
Step 2.
Upon reception of the Keep-alive message, UE-2 responds with a Keep-alive Ack message.
The UE initiating the keep-alive procedure shall determine the follow-up actions based on the result of the signalling, e.g. proceed with implicit layer-2 link release.
Up

6.4.3.6  Layer-2 link management over PC5 reference point for 5G ProSe UE-to-Network Relay  p. 126

The Layer-2 link procedures over PC5 reference point for unicast mode 5G ProSe Direct Communication as depicted from clause 6.4.3.1 to clause 6.4.3.5 can be used for the PC5 reference point between 5G ProSe Remote UE and 5G ProSe UE-to-Network Relay, with the following differences and clarifications:
  • The Layer-2 link modification procedure is applicable to ProSe Communication via 5G ProSe Layer-3 UE-to-Network Relay, other procedures are applicable to both ProSe Communication via 5G ProSe Layer-2 UE-to-Network Relay and ProSe Communication via 5G ProSe Layer-3 UE-to-Network Relay.
  • The UE oriented Layer-2 link establishment is used with UE-1 representing the 5G ProSe Remote UE and UE-2 representing the 5G ProSe UE-to-Network Relay. For other procedures either UE-1 represents the 5G ProSe Remote UE and UE-2 represents the 5G ProSe UE-to-Network Relay, or UE-1 represents the 5G ProSe UE-to-Network Relay and UE-2 represents the 5G ProSe Remote UE. I.e. the Layer-2 link establishment is initiated by the 5G ProSe Remote UE, while other procedures may be initiated either by the 5G ProSe Remote UE or by the 5G ProSe UE-to-Network Relay.
For the UE oriented Layer-2 link establishment as described in the clause 6.4.3.1,
  • In step 1, the 5G ProSe Remote UE determines the destination Layer-2 ID for PC5 unicast link establishment based on the unicast source Layer-2 ID of the selected 5G ProSe UE-to-Network Relay (as specified in clause 5.8.3) during UE-to-Network Relay discovery as specified in clause 6.3.2.3.
  • In step 2, 5G ProSe Remote UE (UE-1) determines the Relay Service Code to be used. The Relay Service Code to be used is selected from the received Relay Service Code(s) during UE-to-Network Relay discovery as specified in clause 6.3.2.3.
  • In step 3, 5G ProSe Remote UE (UE-1) sends a unicast Direct Communication Request message to the selected 5G ProSe UE-to-Network Relay. The destination Layer-2 ID used to send the Direct Communication Request message shall be unicast Layer-2 ID as determined in step 1. The Direct Communication Request message includes:
    • Source User Info: the identity of the Remote UE requesting relay operation (i.e. User Info ID).
    • Target User Info: the identity of the UE-to-Network Relay provided to the 5G ProSe Remote UE during UE-to-Network Relay Discovery procedure (i.e. User Info ID).
    • Relay Service Code: indicates the connectivity service (which may be non-emergency or emergency) provided by the 5G ProSe UE-to-Network Relay as requested by the 5G ProSe Remote UE.
    • Security Information: the information for the establishment of security.
  • In step 4 and step 5, step 4a and step 5a are performed if the 5G ProSe UE-to-Network Relay's identity matches the Target User Info and the Relay Service Code is one of the Relay Service Codes included during UE-to-Network Relay discovery as specified in clause 6.3.2.3. The Source User Info in the Direct Communication Accept message is the identity of the UE-to-Network Relay (i.e. User Info ID). In the case of 5G ProSe Layer-2 UE-to-Network Relay, the Remote UE does not send the IP Address Configuration, Link-Local IPv6 Address and QoS Info to the 5G ProSe Layer-2 UE-to-Network Relay and the Direct Communication Accept message does not include IP Address Configuration, Link-Local IPv6 Address and QoS Info. In the case of 5G ProSe Layer-3 UE-to-Network Relay, the Direct Communication Accept message does not include the IP Address Configuration indicating the value "address allocation not supported".
  • In the case of 5G ProSe Layer-2 UE-to-Network Relay, step 6 is not performed.
For the link identifier update as described in the clause 6.4.3.2,
  • Application Layer ID is replaced by User Info ID.
  • In the case of 5G ProSe Layer-2 UE-to-Network Relay, the changed identifiers do not include IP address/prefix.
For the Layer-2 link release as described in the clause 6.4.3.3,
  • In step1, if the Layer-2 link release procedure is initiated by the 5G ProSe UE-to-Network Relay, the Disconnect Request message may indicate the 5G ProSe UE-to-Network Relay is temporarily not available as described in clause 5.12.
  • If the service authorization for acting as a 5G ProSe Remote UE or as a 5G ProSe UE-to-Network Relay is revoked, the 5G ProSe Remote UE or the 5G ProSe UE-to-Network Relay should initiate the release of the layer-2 link that the revoked authorization affects.
  • A 5G ProSe Layer-2 Remote UE or a 5G ProSe Layer-2 UE-to-Network Relay initiates the release of the layer-2 link upon receiving an indication from its AS layer to trigger PC5 unicast link release as specified in TS 38.331.
A 5G ProSe Remote UE and a 5G ProSe UE-to-Network Relay shall set up a separate PC5 unicast links if an existing unicast link(s) was established with a different Relay Service Code or without a Relay Service Code.
Each PC5 unicast link for 5G ProSe UE-to-Network Relay is associated with a Unicast Link Profile, which includes:
  • User Info ID and Layer-2 ID of 5G ProSe Remote UE; and
  • User Info ID and Layer-2 ID of 5G ProSe UE-to-Network Relay; and
  • Relay Service Code; and
  • In the case of 5G ProSe Layer-3 UE-to-Network Relay, the network layer protocol and the information about PC5 QoS Flow(s).
The Unicast Link Profile shall be updated accordingly after a Layer-2 link modification or Layer-2 link identifier update.
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6.4.3.7  Layer-2 link management over PC5 reference point for 5G ProSe UE-to-UE Relay |R18|  p. 127

6.4.3.7.1  Common part for Layer-2 link management over PC5 reference point for 5G ProSe UE-to-UE Relay  p. 127
For the 5G ProSe Communication via 5G ProSe UE-to-UE Relay as described in clause 6.7.1 and clause 6.7.2:
  • The Direct Communication Request message over the first hop PC5 reference point includes:
    • user info (i.e. Application Layer ID) of source 5G ProSe End UE: the identity of the source 5G ProSe End UE requesting relay operation.
    • User Info ID of 5G ProSe UE-to-UE Relay: the identity of the UE-to-UE Relay provided to the source 5G ProSe End UE during 5G ProSe UE-to-UE Relay Discovery procedure.
    • user info (i.e. Application Layer ID) of target 5G ProSe End UE: the identity of the target 5G ProSe End UE provided to the source 5G ProSe End UE during UE-to-UE Relay Discovery procedure.
    • (optional) Destination Layer-2 ID of target 5G ProSe End UE: the unicast destination Layer-2 ID of the target 5G ProSe End UE determined by the source 5G ProSe End UE as specified in clause 5.8.2.4.
    • ProSe Service Info: the information about the ProSe identifier(s) requesting Layer-2 link establishment.
    • RSC: the connectivity service provided by the 5G ProSe UE-to-UE Relay as requested by the source 5G ProSe End UE.
    • Security Information: the information for the establishment of security for the first hop PC5 link establishment (see TS 33.503).
The Direct Communication Request message over the second hop PC5 reference point includes:
  • user info (i.e. Application Layer ID) of source 5G ProSe End UE.
  • user info (i.e. Application Layer ID) of target 5G ProSe End UE.
  • User Info ID of 5G ProSe UE-to-UE Relay.
  • ProSe Service Info: the information about the ProSe identifier(s).
  • RSC: the connectivity service provided by the 5G ProSe UE-to-UE Relay as requested by the source 5G ProSe End UE.
  • Security Information: the information for the establishment of security for the second hop PC5 link establishment (see TS 33.503).
The Direct Communication Accept message over the second hop PC5 reference point includes:
  • user info (i.e. Application Layer ID) of target 5G ProSe End UE.
The Direct Communication Accept message over the first hop PC5 reference point includes:
  • user info (i.e. Application Layer ID) of target 5G ProSe End UE.
  • User Info ID of 5G ProSe UE-to-UE Relay.
The Link Modification Request message over the first hop PC5 reference point includes:
  • user info (i.e. Application Layer ID) of target 5G ProSe End UE: the identity of the target 5G ProSe End UE provided to the source 5G ProSe End UE during UE-to-UE Relay Discovery procedure.
  • (optional) Destination Layer-2 ID of target 5G ProSe End UE: the unicast destination Layer-2 ID of the target 5G ProSe End UE determined by the source 5G ProSe End UE as specified in clause 5.8.2.4.
The Link Modification Request message over the second hop PC5 reference point includes:
  • user info (i.e. Application Layer ID) of source 5G ProSe End UE.
  • user info (i.e. Application Layer ID) of target 5G ProSe End UE.
The Link Modification Accept message over the second hop PC5 reference point includes:
  • user info (i.e. Application Layer ID) of target 5G ProSe End UE.
The Link Modification Accept message over the first hop PC5 reference point includes:
  • user info (i.e. Application Layer ID) of target 5G ProSe End UE.
Each end-to-end unicast link for 5G Layer-2 ProSe UE-to-UE Relay is associated with a Unicast Link Profile, which includes:
  • user info (i.e. Application Layer ID) and Layer-2 ID of source 5G ProSe End UE; and
  • user info (i.e. Application Layer ID) and Layer-2 ID of target 5G ProSe End UE; and
  • Relay Service Code; and
  • information about PC5 QoS Flow(s).
Each PC5 unicast link for 5G Layer-3 ProSe UE-to-UE Relay over the first hop is associated with a Unicast Link Profile, which includes:
  • user info (i.e. Application Layer ID) and Layer-2 ID of the 5G ProSe End UE; and
  • User Info ID and Layer-2 ID of 5G ProSe UE-to-UE Relay; and
  • Relay Service Code; and
  • the network layer protocol and the information about PC5 QoS Flow(s).
Each PC5 unicast link for 5G Layer-3 ProSe UE-to-UE Relay over the second hop is associated with a Unicast Link Profile, which includes:
  • User Info ID and Layer-2 ID of 5G ProSe UE-to-UE Relay; and
  • user info (i.e. Application Layer ID) and Layer-2 ID of the 5G ProSe End UE; and
  • Relay Service Code; and
  • the network layer protocol and the information about PC5 QoS Flow(s).
The Unicast Link Profile shall be updated accordingly after a Layer-2 link modification or Layer-2 link identifier update.
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6.4.3.7.2  Layer-2 link management over PC5 reference point for 5G ProSe Layer-2 UE-to-UE Relay  p. 129
For the 5G ProSe Communication via 5G ProSe Layer-2 UE-to-UE Relay as described in clause 6.7.2, the description in clause 6.4.3.7.1 applies. In the case of ProSe communication via 5G ProSe Layer-2 UE-to-UE Relay, an end-to-end Direct Communication Request message between the source 5G ProSe End UE and the target 5G ProSe End UE is transmitted after the per-hop connections have been established. The information from end-to-end unicast link profile in clause 6.4.3.7.1 is used for mapping of the destination Layer-2 ID as specified in TS 38.300 and TS 38.331.
The message contents over PC5 reference point for unicast mode 5G ProSe Direct Communication as depicted from clause 6.4.3.1 to clause 6.4.3.5 are same for the end-to-end connection between peer 5G ProSe End UEs.
When the 5G ProSe End UEs initiate End-to-End PC5-S signalling to release an end-to-end ProSe link via 5G ProSe Layer 2 UE-to-UE relay, the 5G ProSe End UE which has initiated the PC5-S release procedure triggers Layer-2 link modification or a Layer-2 link release procedure as described in clause 6.4.3.7 towards 5G ProSe Layer-2 UE-to-UE relay.
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6.4.3.7.3  Layer-2 link management over PC5 reference point for 5G ProSe Layer-3 UE-to-UE Relay  p. 129
For the 5G ProSe Communication via 5G ProSe Layer-3 UE-to-UE Relay as described in clause 6.7.1, the description in clause 6.4.3.7.1 applies with following differences and clarifications:
  • In the Security Procedure of the first hop PC5 reference point, the source 5G ProSe Layer-3 End UE provides the IP Address Configuration or Link-Local IPv6 Address and QoS Info of the end-to-end QoS to the 5G ProSe Layer-3 UE-to-UE Relay. If the PC5 link is used for transferring Ethernet traffic, the source 5G ProSe Layer-3 End UE provides its Ethernet MAC address instead of IP related information.
  • In the Security Procedure of the second hop PC5 reference point, the 5G ProSe Layer-3 UE-to-UE Relay provides the IP Address Configuration or Link-Local IPv6 Address and QoS Info of the second hop QoS to the target 5G ProSe End UE. If the PC5 link is used for transferring Ethernet traffic, the 5G ProSe Layer-3 UE-to-UE Relay provides the Ethernet MAC address of the source 5G ProSe Layer-3 End UE instead of IP related information.
  • The Direct Communication Accept message over the second hop PC5 reference point additionally includes IP Address Configuration or Link-Local IPv6 Address and QoS Info of the second hop QoS. If the PC5 link is used for transferring Ethernet traffic, the target 5G ProSe Layer-3 End UE provides its Ethernet MAC address instead of IP related information.
  • The 5G ProSe Layer-3 UE-to-UE Relay decides the QoS Info of the first hop QoS with considering the received second hop QoS, the Direct Communication Accept message over the first hop PC5 reference point additionally includes IP Address Configuration or Link-Local IPv6 Address, QoS Info of the first hop QoS and may include IP address of the target 5G ProSe End UE. If the PC5 link is used for transferring Ethernet traffic, 5G ProSe Layer-3 UE-to-UE Relay provides the Ethernet MAC address of the target 5G ProSe Layer-3 End UE instead of IP related information.
  • For adding new end-to-end QoS flow or modifying existing end-to-end QoS flow, in the Link Modification Request message over the first hop PC5 reference point, the source 5G ProSe End UE additionally includes QoS Info of the end-to-end QoS as described in the clause 6.4.3.4. For removing end-to-end QoS flows(s), in the Link Modification Request message over the first hop PC5 reference point, the source 5G ProSe End UE includes PFI(s) of the QoS flow(s) of the first hop as described in the clause 6.4.3.4. If the PC5 link is used for transferring Ethernet traffic, the source 5G ProSe Layer-3 End UE may provide its Ethernet MAC address.
  • For adding new end-to-end QoS flow or modifying existing end-to-end QoS flow, in the Link Modification Request message over the second hop PC5 reference point, the 5G ProSe Layer-3 UE-to-UE Relay additionally includes QoS Info of the second hop QoS to the target 5G ProSe End UE. For removing end-to-end QoS flow(s), in the Link Modification Request message over the second hop PC5 reference point, the 5G ProSe Layer-3 UE-to-UE Relay includes PFI(s) of the QoS flow(s) of the second hop. If the PC5 link is used for transferring Ethernet traffic, the 5G ProSe Layer-3 UE-to-UE Relay provides the Ethernet MAC address of the source 5G ProSe Layer-3 End UE.
  • For adding new end-to-end QoS flow or modifying existing end-to-end QoS flow, the Link Modification Accept message over the second hop PC5 reference point additionally includes QoS Info of the second hop QoS. If the PC5 link is used for transferring Ethernet traffic, the target 5G ProSe Layer-3 End UE may provide its Ethernet MAC address.
  • For adding new end-to-end QoS flow or modifying existing end-to-end QoS flow, the 5G ProSe Layer-3 UE-to-UE Relay decides the QoS Info of the first hop QoS with considering the received second hop QoS, the Link Modification Accept message over the first hop PC5 reference point additionally includes QoS Info of the first hop QoS and may include IP address of the target 5G ProSe End UE. If the PC5 link is used for transferring Ethernet traffic, 5G ProSe Layer-3 UE-to-UE Relay provides the Ethernet MAC address of the target 5G ProSe Layer-3 End UE instead of IP related information.
When the PC5 link between a 5G ProSe Layer-3 End UE and the 5G ProSe Layer-3 UE-to-UE Relay is released, the 5G ProSe Layer-3 UE-to-UE Relay may initiate the PC5 link release to the peer 5G ProSe Layer-3 End UE(s) or notify the peer 5G ProSe Layer-3 End UE(s) the peer PC5 link is released.
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6.4.3.7.4  Layer-2 link management over PC5 reference point for 5G ProSe UE-to-UE Relay Communication with integrated Discovery  p. 130
This clause is for the 5G ProSe UE-to-UE Relay Communication with integrated Discovery procedure as described in clause 6.7.3.
The Direct Communication Request message over the first hop PC5 reference point includes:
  • user info (i.e. Application Layer ID) of source 5G ProSe End UE.
  • (optional) user info (i.e. Application Layer ID) of target 5G ProSe End UE: the identity of the target 5G ProSe End UE if provided from the ProSe application layer.
  • (optional) Destination Layer-2 ID of target 5G ProSe End UE: the unicast destination Layer-2 ID of the target 5G ProSe End UE determined by the source 5G ProSe End UE as specified in clause 5.8.2.4.
  • ProSe Service Info: the information about the ProSe identifier(s) requesting Layer-2 link establishment.
  • RSC: the connectivity service provided by the 5G ProSe UE-to-UE Relay as requested by the source 5G ProSe End UE.
  • Relay_indication: indicates whether a 5G ProSe UE-to-UE Relay can send a Direct Communication Request message based on the received Direct Communication Request message which contains the relay_indication.
  • Security Information: the information for the establishment of security for the first hop PC5 link establishment (see TS 33.503).
The Direct Communication Request message over the second hop PC5 reference point includes:
  • user info (i.e. Application Layer ID) of source 5G ProSe End UE.
  • User Info ID of 5G ProSe UE-to-UE Relay.
  • (optional) user info of target 5G ProSe End UE.
  • ProSe Service Info: the information about the ProSe identifier(s).
  • RSC: the connectivity service provided by the 5G ProSe UE-to-UE Relay as requested by the source 5G ProSe End UE.
  • Security Information: the information for the establishment of security for the second hop PC5 link establishment (see TS 33.503).
The Direct Communication Accept message over the second hop PC5 reference point includes:
  • user info (i.e. Application Layer ID) of target 5G ProSe End UE.
The Direct Communication Accept message over the first hop PC5 reference point includes:
  • user info (i.e. Application Layer ID) of target 5G ProSe End UE.
  • User Info ID of 5G ProSe UE-to-UE Relay.
For the 5G ProSe Communication via 5G ProSe Layer-3 UE-to-UE Relay, additional clarifications are as following:
  • In the Security Procedure of the second hop PC5 reference point, the 5G ProSe Layer-3 UE-to-UE Relay provides the IP Address Configuration or Link-Local IPv6 Address to the target 5G ProSe End UE.
  • The Direct Communication Accept message over the second hop PC5 reference point additionally includes IP Address Configuration or Link-Local IPv6 Address (if IP communication is used), Ethernet MAC address of target 5G ProSe End UE (if Ethernet communication is used). QoS Info is not included in the Security Procedure or Direct Communication Accept message of the second hop PC5 reference point.
  • In the Security Procedure of the first hop PC5 reference point, the source 5G ProSe End UE provides the IP Address Configuration, Link-Local IPv6 Address and QoS Info of the end-to-end QoS to the 5G ProSe Layer-3 UE-to-UE Relay.
  • The 5G ProSe Layer-3 UE-to-UE Relay provides the QoS info of the second hop QoS to the target 5G ProSe End UE using the Layer-2 link modification as described in the clause 6.4.3.4.
  • The 5G ProSe Layer-3 UE-to-UE Relay decides the QoS Info of the first hop QoS with considering the received second hop QoS from the target 5G ProSe End UE, the Direct Communication Accept message over the first hop PC5 reference point additionally includes IP Address Configuration or Link-Local IPv6 Address, QoS Info of the first hop QoS and may include IP address of the target 5G ProSe End UE (if IP communication is used) or Ethernet MAC address of target 5G ProSe End UE (if Ethernet communication is used).
For the 5G ProSe Communication via 5G ProSe Layer-2 UE-to-UE Relay, the message contents over PC5 reference point for unicast mode 5G ProSe Direct Communication as depicted from clause 6.4.3.1 to clause 6.4.3.5 are same for the end-to-end connection between peer 5G ProSe End UEs.
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6.4.3.8  Layer-2 link management over PC5 reference point for 5G ProSe multi-hop UE-to-Network Relay |R19|  p. 131

6.4.3.8.1  Layer-2 Link establishment and management (based on Model A discovery)  p. 131
Each of the 5G ProSe Intermediate UE-to-Network Relay establishes a Layer-2 Link with its immediate parent Intermediate UE-to-Network Relay or the 5G ProSe UE-to-Network Relay, before it can serve the 5G ProSe Remote UE, or a child Intermediate UE-to-Network Relay. RSC based configuration for the 5G ProSe Intermediate UE-to-Network Relay indicates whether it should establish the Layer-2 Link with a parent relay before it can participate in the discover operation.
Layer-2 link management procedures as defined in clause 6.4.3.6 for 5G ProSe UE-to-Network Relay operation are used. When establishing the Layer-2 link with its parent relay (either a 5G ProSe UE-to-Network Relay or another 5G ProSe Intermediate UE-to-Network Relay), the 5G ProSe Intermediate UE-to-Network Relay takes the role of the 5G ProSe Remote UE and its parent relay takes the role of 5G ProSe UE-to-Network Relay. The Layer-2 link is established per RSC.
The 5G ProSe Remote UE uses the procedure defined in clause 6.4.5.6 to establish a Layer-2 Link with the selected 5G ProSe Intermediate UE-to-Network Relay. The Intermediate UE-to-Network Relay takes the role of of 5G ProSe UE-to-Network Relay in the procedure.
When an Intermediate UE-to-Network Relay has a child Intermediate UE-to-Network Relay or a 5G ProSe Remote UE connected, it updates the Layer-2 link with its parent relay, using the procedure defined in clause 6.4.3.4, with the following enhancements:
  • The link modification procedure is enhanced to inform the parent relay, e.g. another 5G ProSe Intermediate UE-to-Network Relay or the 5G ProSe UE-to-Network Relay, of the User Info of the child relay(s) or the Remote UE(s). The Link Modification Request message contains a list of 5G ProSe Remote UE (Remote User ID, Remote UE Info) and the corresponding PC5 QoS Flow associated with each 5G ProSe Remote UE. The Remote User ID and Remote UE Info are as defined in clause 6.5.1.1.
An Intermediate UE-to-Network Relay triggers a link modification procedure towards its parent relay if a new Remote User ID is received from its child relay during the link modification procedure.
The 5G ProSe UE-to-Network Relay's Remote UE reporting procedure includes all the Remote UE information reported by its child relays.
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6.4.3.8.2  IP address/prefix management for 5G ProSe Layer-3 Multi-hop UE-to-Network Relay  p. 132
When IP based PDU session types are used by the 5G ProSe UE-to-Network Relay, the Intermediate UE-to-Network Relay needs to act as an IP Router.
The actual IP address allocation is performed by the 5G ProSe UE-to-Network Relay, as defined in clause 6.5.1.
To support DHCP based IP address configuration, the 5G ProSe Intermediate UE-to-Network Relay acts as a DHCPv4 or DHCPv6 proxy. To support IPv6 SLAAC, the 5G ProSe Intermediate UE-to-Network Relay also relays the Router Solicitation and Router Announcement messages between the 5G ProSe Remote UE and the 5G ProSe UE-to-Network Relay.
The 5G ProSe Intermediate UE-to-Network Relay builds its local IP routing table based on the Remote UE info from the link modification procedures as described in clause 6.4.3.8.1. The local IP routing table is per RSC and used based on RSC of the link the packet is received.
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6.4.3.8.3  Relay reselection and mobility support  p. 132
There are two types of situations for parent relay reselection, i.e. for a single 5G ProSe Remote UE, and for a 5G ProSe Intermediate UE-to-Network Relay with multiple child relays or 5G ProSe Remote UEs.
For a single 5G ProSe Remote UE, when the connection with an old parent relay (either a 5G ProSe Intermediate UE-to-Network Relay or a 5G ProSe UE-to-Network Relay) is lost or the link quality drops below a configured threshold, the 5G ProSe Remote UE triggers the reselection of the relays that offers the same service, identified by the same RSC.
Copy of original 3GPP image for 3GPP TS 23.304, Fig. 6.4.3.8.3-1: Relay reselection for 5G ProSe Remote UE with 5G ProSe Multi-hop UE-to-Network Relays
Figure 6.4.3.8.3-1: Relay reselection for 5G ProSe Remote UE with 5G ProSe Multi-hop UE-to-Network Relays
(⇒ copy of original 3GPP image)
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Figure 6.4.3.8.3-1 depicts the Relay reselection operation for this situation. When the 5G ProSe Remote UE has lost the connection or has an imminent connection loss/deteriorated connection with the 5G ProSe Intermediate UE-to-Network Relay-1, the 5G ProSe Remote UE performs relay reselection by using the relay discovery procedure in clause 6.3.2.5. The 5G ProSe Remote UE discovered the 5G ProSe Intermediate UE-to-Network Relay-2 that offers the same RSC. In case there are multiple 5G ProSe Intermediate UE-to-Network Relays discovered, the 5G ProSe Intermediate UE-to-Network Relay that offers connection to the same 5G ProSe UE-to-Network Relay is prioritized.
5G ProSe Remote UE establishes the Layer-2 link with the 5G ProSe Intermediate UE-to-Network Relay-2 as specified in clause 6.4.3.8.1. After the connection establishment, the Intermediate UE-to-Network Relay-2 uses the Layer-2 Link Modification procedure to update the 5G ProSe UE-to-Network Relay regarding the 5G ProSe Remote UE. If the same 5G ProSe UE-to-Network Relay is used, it switches the connection/routing context for the 5G ProSe Remote UE from the Layer-2 link with the 5G Intermediate UE-to-Network Relay-1 to that of the Layer-2 link with the 5G ProSe Intermediate UE-to-Network Relay-2.
The 5G ProSe Remote UE tears down the link with the 5G ProSe Intermediate UE-to-Network Relay-1 (or the link failure is detected), which will trigger the 5G ProSe Intermediate UE-to-Network Relay-1 to update the 5G ProSe UE-to-Network Relay to remove its association with 5G ProSe Remote UE.
If the same 5G ProSe UE-to-Network Relay is selected after the relay reselection, the 5G ProSe Remote UE can keep its IP address/prefix (in case of Layer-3 UE-to-Network relay).
If a new 5G ProSe UE-to-Network Relay is used after the relay reselection, the procedures as that described in clause 6.4.3.8.1 will be executed. In this case, IP address/prefix changes may happen (in case of Layer-3 UE-to-Network relay).
The relay reselection procedure can be used by a 5G ProSe Intermediate UE-to-Network Relay, taking the role of the 5G ProSe Remote UE in the procedure.
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6.4.3.9  Layer-2 link management over PC5 reference point for Multi-hop 5G ProSe UE-to-Network Relay (based on Model B Discovery) |R19|  p. 133

The Layer-2 link procedures over PC5 reference point for unicast mode 5G ProSe Direct Communication as depicted from clause 6.4.3.6 is used for the PC5 reference point among the 5G ProSe Remote UE, the 5G ProSe Intermediate UE-to-Network Relay and the UE-to-Network Relay after Model B Discovery, with the following differences and clarifications:
For the UE oriented Layer-2 link establishment as described in the clause 6.4.3.1,
  • The 5G ProSe Remote UE determines the destination Layer-2 ID for PC5 unicast link establishment based on the unicast source Layer-2 ID of the selected 5G ProSe Intermediate Relay (as specified in clause 5.8.3) during UE-to-Network Relay discovery as specified in clause 6.3.2.5.3.
  • The 5G ProSe Intermediate Relay determines the destination Layer-2 ID for PC5 unicast link establishment based on the unicast source Layer-2 ID of the selected 5G ProSe Intermediate Relay or UE-to-Network Relay (as specified in clause 5.8.3) during UE-to-Network Relay discovery as specified in clause 6.3.2.5.3.
  • 5G ProSe Remote UE sends a unicast Direct Communication Request message to the selected 5G ProSe Intermediate Relay. The Direct Communication Request message additionally includes:
    • Path information: an (ordered) list of User Info ID of 5G ProSe Intermediate Relays and the UE-to-Network Relay selected by the 5G ProSe Remote UE based on the path information provided to the 5G ProSe Remote UE during 5G ProSe UE-to-Network Relay Discovery procedure.
    • QoS Info: indicates the End to End QoS Info.
  • 5G ProSe Intermediate Relay sends a unicast Direct Communication Request message to the next 5G ProSe Intermediate Relay or the UE-to-Network Relay according to the path information in the received Direct Communication Request message. The Direct Communication Request message additionally includes:
    • Path information: an (ordered) list of User Info ID of 5G ProSe Intermediate Relays and the UE-to-Network Relay selected by the 5G ProSe Remote UE based on the path information provided to the 5G ProSe Remote UE during 5G ProSe UE-to-Network Relay Discovery procedure.
    • QoS Info: End to End QoS Info and the remaining QoS Info of hops from the Intermediate Relay to the network.
  • In step 4 and step 5, step 4a and step 5a are performed if the 5G ProSe Intermediate/UE-to-Network Relay's identity matches the Target Info (if any) and the Relay Service Code is one of the Relay Service Codes included during UE-to-Network Relay discovery as specified in clause 6.3.2.5.3.
  • Details of QoS info content is FFS.
For the Layer-2 link release as described in the clause 6.4.3.3,
  • If the Layer-2 link release procedure is initiated by the 5G ProSe Intermediate Relay, the Disconnect Request message may indicate the 5G ProSe UE-to-Network Relay is temporarily not available as described in clause 5.12.
  • If the service authorization for acting as a 5G ProSe Intermediate Relay is revoked, the 5G ProSe Intermediate Relay should initiate the release of the layer-2 link that the revoked authorization affects.
Each PC5 unicast link for 5G ProSe UE-to-Network Relay is associated with a Unicast Link Profile, which additionally includes:
  • Path Information: which contains the User Info ID of Intermediate Relay at the next hop to the Remote UE.
Each PC5 unicast link for 5G ProSe Intermediate Relay is associated with a Unicast Link Profile, which additionally includes:
  • Path Information: which contains the User Info ID of Intermediate Relay or UE-to-Network Relay at the adjancent hop.
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6.4.3.10  Layer-2 link management for 5G ProSe Layer-3 Multi-hop UE-to-UE Relay |R19|  p. 134

6.4.3.10.1  Layer-2 Link establishment and management for IP PDU type  p. 134
For the 5G ProSe Communication via 5G ProSe UE-to-UE Relay as described in clause 6.7.5.2:
  • The Direct Communication Request message over the PC5 reference point (between a 5G ProSe End UE and 5G ProSe Multi-hop UE-to-UE Relay, or between 5G ProSe Multi-hop UE-to-UE Relays) includes:
    • User info (i.e. Application Layer ID) of source 5G ProSe End UE or 5G ProSe Multi-hop UE-to-UE Relay: the identity of the source 5G ProSe End UE or 5G ProSe Multi-hop UE-to-UE Relay requesting the connection establishmet.
    • User Info ID of 5G ProSe Multi-hop UE-to-UE Relay: the identity of the 5G ProSe Multi-hop UE-to-UE Relay provided during the 5G ProSe Multi-hop UE-to-UE Relay Discovery procedure.
    • (optional)ProSe Service Info: the information about the ProSe identifier(s) requesting Layer-2 link establishment.
    • RSC: the connectivity service provided by the 5G ProSe Multi-hop UE-to-UE Relay as requested.
    • Security Information: the information for the establishment of security for the PC5 link establishment (see TS 33.503).
The Direct Communication Accept message over the PC5 reference point (between a 5G ProSe End UE and 5G ProSe Multi-hop UE-to-UE Relay, or between 5G ProSe Multi-hop UE-to-UE Relays) includes:
  • User Info ID of 5G ProSe UE-to-UE Relay.
Other link management procedures as defined in clause 6.4.3 (i.e. Link identifier update in clause 6.4.3.2, Layer-2 link release in clause 6.4.3.3, Layer-2 link modification in clause 6.4.3.4, Layer-2 link maintenance in clause 6.4.3.5) can be used for the layer-2 link without enhancements.
When a new layer-2 link is established, or an existing layer-2 link is released, the 5G ProSe Multi-hop UE-to-UE Relay need to inform the status change internally to the MANET router stack.
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6.4.3.10.2  Layer-2 link establishement and management over PC5 reference point for non-IP PDU type  p. 135
For the 5G ProSe Communication via Multi-hop 5G ProSe Layer-3 UE-to-UE Relay as described in clause 6.7.1a, the description in clause 6.4.3.7.1 applies with following differences and clarifications:
  • The Direct Communication Request message over the PC5 reference point between source End UE and the first hop UE-to-UE Relay additionally includes:
  • Path Information: an (ordered) list of User Info ID of 5G ProSe UE-to-UE Relays selected by the source 5G ProSe End UE based on the path information provided to the source 5G ProSe End UE during 5G ProSe UE-to-UE Relay Discovery procedure.
  • QoS Info: indicates the End to End QoS Info from the source End UE to the target End UE.
The Direct Communication Request message over the PC5 reference point between two UE-to-UE Relays includes:
  • User Info of source 5G ProSe End UE.
  • User Info of target 5G ProSe End UE.
  • Path information.
  • ProSe Service Info: the information about the ProSe identifier(s).
  • RSC: the connectivity service provided by the 5G ProSe UE-to-UE Relay as requested by the source 5G ProSe End UE.
  • Security Information: the information for the establishment of security for the PC5 link establishment between two UE-to-UE Relays or between target End UE and UE-to-UE Relay (see TS 33.503).
  • QoS Info: indicates the rest QoS Info from the UE-to-UE Relay to the target End UE.
The Direct Communication Request message over the PC5 reference point between between the target End UE and UE-to-UE Relay additionally includes:
  • Path information.
  • QoS Info: indicates the rest QoS Info from the UE-to-UE Relay to the target End UE.
The Direct Communication Accept message over the PC5 reference point between target End UE and UE-to-UE Relay additionally includes:
  • QoS Info which is the accepted QoS Info of the hop between target End UE and the last UE-to-UE Relay.
The Direct Communication Accept message over the PC5 reference point between two UE-to-UE Relays includes:
  • User Info of target 5G ProSe End UE.
  • Path information.
  • QoS Info which is the accepted QoS Info of the hop between two UE-to-UE Relays and the accumulated QoS Info of hops from the receiver UE-to-UE Relay to the target End UE.
The Direct Communication Accept message over the PC5 reference point between the source End UE and UE-to-UE Relay additionally includes:
  • Path information.
  • QoS Info which is the accepted QoS Info of the hop between two UE-to-UE Relays and the accumulated QoS Info of hops from the source End UE to the target End UE.
The Link Modification Request message over the PC5 reference point between source End UE and the first hop UE-to-UE Relay additionally includes:
  • Path Information: an (ordered) list of User Info ID of 5G ProSe UE-to-UE Relays provided to the source 5G ProSe End UE during 5G ProSe UE-to-UE Relay Discovery procedure.
  • QoS Info: indicates the End-to-End QoS Info from the source End UE to the target End UE.
The Link Modification Request message over the PC5 reference point between two UE-to-UE Relays includes:
  • User Info of source 5G ProSe End UE.
  • Path Information.
  • User Info of target 5G ProSe End UE.
  • QoS Info: indicates the rest QoS Info from the UE-to-UE Relay to the target End UE.
The Link Modification Request message over the PC5 reference point between the target End UE and UE-to-UE Relay additionally includes:
  • Path Information.
  • QoS Info: indicates the rest QoS Info from the UE-to-UE Relay to the target End UE.
The Link Modification Accept message over the PC5 reference point between the target End UE and UE-to-UE Relay additionally includes:
  • Path information.
  • QoS Info which is the accepted QoS Info of the hop between target End UE and UE-to-UE Relay.
The Link Modification Accept message over the PC5 reference point between two UE-to-UE Relays includes:
  • Path information.
  • QoS Info which is the accepted QoS Info of the hop between two UE-to-UE Relays and the accumulated QoS Info of hops from the UE-to-UE Relay to the target End UE.
The Link Modification Accept message over the PC5 reference point between source End UE and the first UE-to-UE Relay additionally includes:
  • Path information.
  • QoS Info which is the accepted QoS Info of the hop between source End UE and the first UE-to-UE Relay and the accumulated QoS Info of hops from the UE-to-UE Relay to the target End UE.
In the Security Procedure of the PC5 reference point between source End UE and UE-to-UE Relay, the source 5G ProSe Layer-3 End UE provides the QoS Info of the end-to-end QoS to the 5G ProSe Layer-3 UE-to-UE Relay. If the PC5 link is used for transferring Ethernet traffic, the source 5G ProSe Layer-3 End UE provides its Ethernet MAC address. The 5G ProSe Layer-3 UE-to-UE Relay may provide the Ethernet MAC address of the target 5G ProSe Layer-3 End UE in the DCA/LMA message.
In the Security Procedure of the PC5 reference point between two UE-to-UE Relays, a 5G ProSe Layer-3 UE-to-UE Relay provides the QoS Info from itself to the target 5G ProSe Layer-3 UE-to-UE Relay. If the PC5 link is used for transferring Ethernet traffic, the 5G ProSe Layer-3 UE-to-UE Relay provides the Ethernet MAC address of the source 5G ProSe Layer-3 End UE. The 5G ProSe Layer-3 UE-to-UE Relay may provide the Ethernet MAC address of the target 5G ProSe Layer-3 End UE in the DCA/LMA message
In the Security Procedure of the PC5 reference point between target End UE and a UE-to-UE Relay, the 5G ProSe Layer-3 UE-to-UE Relay provides the QoS Info of the last hop QoS to the target 5G ProSe End UE. If the PC5 link is used for transferring Ethernet traffic, the 5G ProSe Layer-3 UE-to-UE Relay provides the Ethernet MAC address of the source 5G ProSe Layer-3 End UE. The target 5G End UE may provide its Ethernet MAC address in the DCA/LMA message
The 5G ProSe Layer-3 UE-to-UE Relay decides the QoS Info of the next hop to source End UE with considering the accumulated QoS Info of the hop(s) to the target End UE which is received in the Direct Communication Accept message.
For adding new end-to-end QoS flow or modifying existing end-to-end QoS flow, the Link Modification Accept message over each PC5 reference point additionally includes QoS Info of that hop. If the PC5 link is used for transferring Ethernet traffic, the target 5G ProSe Layer-3 End UE may provide its Ethernet MAC address. For a path between a specific pair of End UEs, if at least one of the PC5 link is released, the 5G ProSe Layer-3 UE-to-UE Relay(s) in the path may release other PC5 link(s) in the path.
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