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Content for  TS 23.304  Word version:  18.5.1

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6.8  Procedures for communication path switching between PC5 and Uu reference points |R18|p. 135

6.8.1  Procedure for communication path switching from Uu reference point to PC5 reference pointp. 135

Figure 6.8.1-1 depicts the procedure for communication path switching from Uu reference point to PC5 reference point.
Copy of original 3GPP image for 3GPP TS 23.304, Fig. 6.8.1-1: Procedure for communication path switching from Uu reference point to PC5 reference point
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1)
UE-1 and UE-2 communicate with each other via Uu path, i.e. by using established PDU Sessions.
2)
UE-1 decides to perform path switching for ProSe service(s) from Uu path to PC5 path, e.g. because UE-1 and UE-2 are in proximity each other or for offloading some traffic from the network.
UE-1 determines whether and which ProSe service(s) can be switched to PC5 path based on the path selection policy.
3)
UE-1 triggers the establishment of a PC5 unicast link by using the Layer-2 link establishment procedure as specified in clause 6.4.3.1. The PC5 unicast link is established including the ProSe service(s) that can be switched to PC5 path. If any Layer-2 link already established between UE-1 and UE-2 can be used for this path switching, the Layer-2 link modification as specified in clause 6.4.3.4 is used.
4)
Traffic for the ProSe service(s) is switched from Uu path to PC5 path.
5a)
UE-1 may release its PDU Session, e.g. if no traffic transmitted over the PDU Session, or modify its PDU Session, e.g. only part of the services is switched.
5b)
UE-2 may release its PDU Session, e.g. if no traffic transmitted over the PDU Session, or modify its PDU Session, e.g. only part of the services is switched.
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6.8.2  Procedure for communication path switching from PC5 reference point to Uu reference pointp. 136

Figure 6.8.2-1 depicts the procedure for communication path switching from PC5 reference point to Uu reference point.
Copy of original 3GPP image for 3GPP TS 23.304, Fig. 6.8.2-1: Procedure for communication path switching from PC5 reference point to Uu reference point
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1)
UE-1 and UE-2 communicate with each other via PC5 path, i.e. by using the established PC5 unicast link between them.
2)
UE-1 decides to path switch ProSe service(s) from PC5 path to Uu path, e.g. if the PC5 signal strength of the unicast link with UE-2 reaches or below certain configured signal strength threshold.
UE-1 determines whether and which ProSe service(s) can be switched to Uu path based on e.g. the availability of the Uu path, the path selection policy, etc.
UE-1 sends a Path Switch Request message to UE-2 to negotiate the ProSe service(s) to be switched. UE-1 includes the ProSe service(s) that can be switched to Uu path in the Path Switch Request message.
Optionally, UE-1 can decide the Uu QoS parameters of each UE based on PC5 QoS parameters for each ProSe service. UE-1 may include Uu QoS parameters used for UE-2's Uu path for the ProSe service(s) that can be switched to a Uu path in the Path Switch Request message.
3)
UE-2 responds with a Path Switch Response message.
UE-2 determines whether and which ProSe service(s) can be switched to Uu path based on e.g., the path selection policy, availability of Uu path, etc.
If UE-2 accepts the path switch request from UE-1, UE-2 includes the accepted ProSe service(s) to be switched to Uu path in the Path Switch Response message from those indicated by UE-1. Otherwise, UE-2 rejects the path switch request with the appropriate cause (e.g. path switching to Uu path for the ProSe service(s) is not permitted, Uu path is not available) in the Path Switch Response message.
4a)
UE-1 may establish or modify PDU Session by using the PDU session establishment procedure as specified in clause 4.3.2 or the PDU session modification procedure as specified in clause 4.3.3 of TS 23.502. UE-1 may set the Requested QoS as the Uu QoS parameters used for UE-1's Uu path for the specific accepted ProSe service in the PDU Session Modification Request. The PDU Session needs to support QoS requirements for the ProSe service(s) to be switched from PC5 path.
4b)
UE-2 may establish or modify PDU Session by using the PDU session establishment procedure as specified in clause 4.3.2 or the PDU session modification procedure as specified in clause 4.3.3 of TS 23.502. UE-2 may set the Requested QoS as the Uu QoS parameters used for UE-2's Uu path for the specific accepted ProSe service in the PDU Session Modification Request. The PDU Session needs to support QoS requirements for the ProSe service(s) to be switched from PC5 path.
5)
Traffic for the accepted ProSe service(s) is switched from PC5 path to Uu path.
6)
The PC5 unicast link may be released, e.g. if no more ProSe services over the PC5 unicast link.
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6.9  Multi-path communication via Uu and via 5G ProSe UE-to-Network Relay |R18|p. 138

6.9.1  Generalp. 138

This clause describes the procedures to support multi-path communication via direct Uu path and via 5G ProSe UE-to-Network Relay.

6.9.2  Multi-path communication via direct Uu path and via 5G ProSe Layer-3 UE-to-Network Relayp. 138

When a 5G ProSe enabled UE accesses the network, if the UE decides to establish multi-path via direct Uu path and via the 5G ProSe Layer-3 UE-to-Network Relay without N3IWF based on "ProSe Multi-path Preference" in the selected RSD of the matched URSP rule for the application traffic as specified in clause 6.5.4, the following is performed:
  • The UE may establish a new PDU Session as specified in clause 4.3.2 of TS 23.502 or modify an existing PDU Session as specified in clause 4.3.3 of TS 23.502 for the direct Uu path.
  • The UE takes the role of 5G ProSe Layer-3 Remote UE either establishes 5G ProSe Communication via 5G ProSe Layer-3 UE-to-Network Relay without N3IWF as specified in clause 6.5.1.1 or modifies an existing PC5 connection with a 5G ProSe Layer-3 UE-to-Network Relay as specified in clause 6.4.3.6.
When a 5G ProSe enabled UE accesses the network, if the UE decides to establish multi-path via direct Uu path and via the 5G ProSe Layer-3 UE-to-Network Relay with N3IWF based on the "multi-access" Access Type of the selected RSD, the UE establishes a MA PDU Session as specified in clause 4.22 of TS 23.502, the following is performed:
  • The UE sets up path over Uu by establishing a MA PDU session using the procedures for 3GPP access in clause 4.22 of TS 23.502.
  • The UE taking the role of 5G ProSe Layer-3 Remote UE, if not connected and registered to the network via a Layer-3 UE-to-Network Relay with N3IWF, performs Relay (re)selection and performs registration with 5GC as specified in clause 6.5.1.2 and then performs MA PDU Session Establishment procedure or adds the user plane resources over the path via 5G ProSe Layer-3 UE-to-Network Relay with N3IWF using the procedures for non-3GPP access in clause 4.22 of TS 23.502.
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6.9.3  Multi-path communication via direct Uu path and via 5G ProSe Layer-2 UE-to-Network Relayp. 138

Procedures for Multi-path communication via direct Uu path and via 5G ProSe Layer-2 UE-to-Network Relay is specified in TS 38.300.
In the case that the direct Uu path and indirect path via 5G Prose Layer-2 UE-to-Network Relay connect via different cells of the same NG-RAN, the NG-RAN shall provide the cell ID of the direct path in the ULI information. The same applies to NG-RAN Location reporting procedures defined in clause 4.10 of TS 23.502 if AMF enables location reporting towards NG-RAN.
Path management of the 5G ProSe Layer-2 Remote UE is specified in clause 16.21 of TS 38.300.
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