3GPP TSG-RAN WG2 Meeting #130                                                        R2-2503433
St.Julians, Malta, May 19th – 23rd, 2025

Source:	CATT
Title:	Intra-gNB Service Continuity for Multi-hop U2N Relay
Agenda Item:	8.13.4
Document for:	Discussion and Decision

Conclusion
According to the analysis in section 2, it is proposed:
For Scenario C
Proposal 1: Suggest RAN2 to adopt Figure-1 as the baseline signaling flow for intra-gNB direct to multi-hop indirect path switching.
Proposal 2: (RRC-02) For Remote UE measurement reporting in scenario C/D, it will include legacy reporting content with the L2 ID and the sidelink measurement quantity result of only the candidate First Relay UE, and the serving cell ID of the Last Relay UE. 
Proposal 3: It is network implementation to find a target multi-hop relay link with indirect RRC connection for First/Intermediate Relay UE and direct RRC connection for Last Relay UE. 
Proposal 4: (RRC-01) The UE will perform the legacy measurement event Y1/Y2, the description on candidate L2 U2N Relay UE in event Y1/Y2 already includes the candidate First Relay UE regarding the agreed definition of L2 U2N Relay UE. 
For Scenario D
Proposal 5: (RRC-03) For Scenario D, RAN2 does not specify anything to support the case that the source single-hop Relay UE is the target First/Intermediate Relay UE using a single procedure. This case can be handled in the baseline control plane model, if necessary and subject to network implementation, by sequential path switches for the remote UE and the source Relay UE.
Proposal 6: (RRC-03) For scenario D, RAN2 will support the case that the source single-hop relay UE is the last relay UE on the target path using the Rel-19 I2M path switching with different target last relay UEs as baseline. Spec impact will be minimised.
Proposal 7: Suggest RAN2 to adopt Figure-2 as the baseline signaling flow for intra-gNB single-hop indirect to multi-hop indirect path switching.
Proposal 8: (RRC-02) The UE will perform the legacy measurement event X2/Y2/Z1, the description on candidate L2 U2N Relay UE in event Y2/Z1 already includes the candidate First Relay UE regarding the agreed definition of L2 U2N Relay UE. 

3GPP TSG-RAN WG2 Meeting #130	R2-2503491
St.Julians, Malta, May 19th – 23rd, 2025	

Agenda Item:	8.13.4
Source:	OPPO
Title:	Service continuity of multi-hop U2N relay  
Document for:	Discussion, Agreement

Conclusion
We have the following observations:
Observation 1	With the restriction in the WID that all the relay UEs on the target multi-hop path, from both UE and network perspective, there is no much difference for multi-hop target path and single-hop target path.
Observation 2	With the understanding that the “first relay” in multi-hop relay is the serving or candidate relay to be reported, Y1/Y2/Z1 can be reused for the path switching to multi-hop indirect path.
Observation 3	It is sufficient to report L2 ID, Cell ID, and the RSRP of the first relay (as candidate L2 U2N Relay) since all the relay UEs at the multi-hop relay link are in RRC connected state to the same cell in the same gNB.
Observation 4	For the path switching execution to multi-hop indirect path, gNB can decide the target path based on the information from the remote UE and do the reconfiguration for the relay UEs at the target path and the remote UE as in legacy.
Observation 5	As agreed for the baseline procedure, the remote UE just measures the serving/candidate relays and trigger measurement report based on network configuration.

We have the following proposals:
Proposal 1	(RRC-1) RAN2 to confirm event Y1/Y2/Z1 can be reused in path switching to multi-hop indirect path with the understanding that the “first relay” in multi-hop relay is the “candidate” relay to be reported.
Proposal 2	(RRC-2) RAN2 to confirm that the measurement reporting from remote UE which includes L2 ID, serving cell ID, and SD-RSRP of the candidate first relay, as in legacy, is sufficient for the path switching to multi-hop indirect path.
Proposal 3	(RRC-3) RAN2 to confirm for scenario D, no differentiation is needed for the case where the intermediated/last relay at the target side 1) is, or 2) is not the U2N relay UE at the source side.
Proposal 4	RAN2 to confirm for scenario B, no differentiation is needed for the cases where the U2N Relay at the target side 1) is, or 2) is not the intermediate/last relay at the source side.

3GPP TSG-RAN WG2 Meeting #130	R2-2503678
St Julian, Malta, 19th – 23rd May 2025

Agenda item:	8.13.4
Source: 	China Telecom
Title:	Discussion on service continuity for multi-hop relay
WID/SID:	NR_SL_relay_multihop
Document for:	Discussion and Decision

Conclusion
In this contribution, we discuss general aspects on service continuity second priority scenarios in multi-hop U2N relay. 
Proposal 1: For intra-gNB direct to multi-hop indirect path switching (i.e. Scenario C), (remote) UE switched to candidate U2N relay within the same gNB is supported. The target U2N relay could be same as or different from the previous serving cell of (remote) UE.
Proposal 2: Event Y1/ Y2 could be used for intra-gNB direct to multi-hop indirect path switching. The PC5 quality between the remote UE and candidate U2N relay/candidate first relay is considered for evaluating Event Y1/ Y2.
Proposal 3: For Intra-gNB single-hop indirect to multi-hop indirect path switching (i.e. Scenario D), remote UE switched to different relays within the same gNB is supported. The serving cell of the new relays could be the same as or different from the previous serving cell of the remote UE.
Proposal 4: Event Z1/X2/Y2 could be used for Intra-gNB single-hop indirect to multi-hop indirect path switching. The remote UE shall consider the first relay as serving L2 U2N relay for evaluating Event Z1/X2.
Proposal 5: For Case D-5/6 in intra-gNB single-hop indirect to multi-hop indirect path switching scenario, RAN2 does not specify anything to support these cases by using a single procedure. These cases can be handled by network implementation, e.g. by sequential path switches for the remote UE and the target intermediate relay UE.

3GPP TSG-RAN WG2 Meeting #130	R2-2503781
St Julian’s, Malta, May 19th – 23th, 2025

Agenda Item:	8.13.4
Source: 	NEC
Title:	Considerations on Service Continuity of Multi-hop Relay
Document for:	Discussion/Decision

Conclusion
Based on the discussion in this document, we have the following observations and proposals:
Observation 1:	The intermediate Relay UE staying in RRC_INACTIVED or RRC_IDLE may trigger cell reselection or relay reselection, which may lead to the service interruption of Remote UE.

Proposal 1:	Upon cell reselection or relay UE reselection, the intermediate relay UE can send notification message to the Remote UE. As a result, the Remote UE can perform RRC connection reestablishment procedure accordingly.
Proposal 2:	RAN2 should discuss whether to allow the U2N last relay UE and/or U2N intermediate relay UE to perform role type change while maintain the PC5-RRC connection with U2N remote UE for service continuity.

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3GPP TSG-RAN WG2 Meeting #129bis	R2-2503927
Wuhan, China, Apr. 7th – 11th, 2025	
	

Agenda Item	: 8.13.4
Source	: LG Electronics Inc.
Title	: Discussion on service continuity for multi-hop U2N relay
Document for	: Discussion and Decision
1.	

Conclusion
Proposal 1: For scenario C, the legacy path-switching command and procedure are reused for the Remote UE and the target first Relay UE. Upon receiving the path-switching command, the Remote UE performs the legacy UE behavior toward the target first Relay UE. The (first)intermediate/last Relay UE belonging to the target path should be in the RRC-connected state.
Proposal 2: For scenario D, the first Relay UE in the target path is a new relay UE which is not on the source relay path. The legacy path-switching command and procedure are reused for the Remote UE and the first Relay UE in the target path. Upon receiving the path-switching command, the Remote UE performs legacy UE behavior toward the first Relay UE on the target path. The (first)intermediate/last Relay UE belonging to the target path should be in the RRC-connected state.
Proposal 3: The Remote UE doesn’t need to include the hop count of the target path in the measurement report.
Proposal 4: The gNB can configure a scaled timer value depending on the hop count for the path switching. 
Proposal 5: If we apply approach 2 control scheme, it looks hard to support service continuity. 
4.	

3GPP TSG-RAN WG2 Meeting #130	R2-2503930
Saint Julian’s, Malta, 19 – 23 May 2025		

Agenda item:	8.13.4
Source:	Nokia
Title:	Discussion on service continuity for multi-hop relay
WID/SID:	NR_SL_relay_multihop - Release 19
Document for:	Discussion and Decision
1	

Conclusion
This document has made the following proposals:
Proposal 1: RAN2 to discuss whether at least multi-hop service continuity should consider the SL-RSRP/SD-RSRP difference when comparing measurements for relay (re)selection.
Proposal 2: RAN2 to agree that the network may provide a separate SD-RSRP threshold for U2N relay reselection.

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3GPP TSG-RAN WG2 Meeting #129-bis	R2-2504275
St Julian’s, Malta May 19th – 23rd, 2025

Agenda Item:	8.13.4
Source: 	Huawei, HiSilicon
Title: 	Discussion on service continuity for Multi-hop Relay
Document for:	Discussion and Decision

Conclusion
In this paper, we discuss the detailed procedures for scenarios C and D, and the enhancements for the path information reporting and path selection.  We have the following observation and proposals.  
Additionally, the text proposal for all the 4 scenarios is also provided in the annex.
Service Continuity Procedures 
.  
Intra-gNB direct to multi-hop indirect path switching 
Proposal for Open issue RRC-1: Measure Events for scenario C and D
Proposal 1: The triggering Event Y1/Y2 can be adopted and reused in the measurement configuration for the multi-hop U2N relay. 
Proposal 2: The measurement reporting includes at least the L2 ID of the First Relay UE, the First Relay UE’s serving cell ID, and sidelink measurement quantity (SD-RSRP derived by measuring the discovery message broadcasted by the First Relay UE).
Proposal for TS 38.300
Proposal 3: RAN 2 agrees the above procedure in Figure 1 along with the text proposal in the Annex as the baseline for intra-gNB direct to multi-hop indirect path switching procedure and be captured in TS 38.300. 
 
Intra-gNB single-hop indirect to multi-hop indirect path switching 
Proposal for Open issue RRC-1: Measure Events for scenario C and D
Proposal 4: The triggering Event Z1 and Event Z2 (if agreed) can be adopted and reused in the measurement configuration for the multi-hop U2N relay.
Proposal 5: The measurement reporting includes at least the L2 ID of the First Relay UE, the First Relay UE’s serving cell ID, and sidelink measurement quantity (SD-RSRP derived by measuring the discovery message broadcasted by the First Relay UE).
Proposal for TS 38.300
Proposal 6: RAN 2 agree the above procedure in Figure 2 along with the text proposal in the Annex as the baseline for intra-gNB single-hop indirect to multi-hop indirect path switching to be captured in TS 38.300.

Open issue RRC-3: Source relay becomes target for scenario D
Proposal 7: The target last relay UE can be the same as the source single-hop U2N relay UE, but the target first/intermediate relay UE cannot be the source single-hop U2N relay UE.


Multi-hop target relaying path selection
Proposal 8: the gNB can determine the target multi-hop relaying path based on the following information:
First Relay UE’s serving cell ID, and the sidelink measurement quantity between the remote UE and the first relay UE.
The sidelink measurement quantity between the adjacent UEs on the candidate multi-hop relaying path.
The hop number of the relaying path
Proposal 9: The remote UE can get the sidelink measurement quantity information between each adjacent relay UEs  and the RRC State information along the candidate multi-hop relaying path to help determining a better target path.
Proposal 10: The remote UE can obtain the RRC state information of the first relay UE from the discovery message, enabling it to select an appropriate path where all relay UEs are in the RRC_CONNECTED state.

3GPP TSG-RAN WG2 #130	R2-2504344
St. Julians, Malta, 19th – 23rd May 2025

Agenda Item:	8.13.4 
Source:	Ericsson
Title:	Service Continuity for Multi-Hop Relays 
Document for:	Discussion, Decision
1 	

Conclusion
Based on the discussion in the previous sections we draw the following observations:
Observation 1	All nodes expect the second relay UE are in the RRC_CONNECTED state via the indirect path to the gNB.
Observation 2	Triggering the relay reselection procedure at the remote UE due to path switch/handover of any of the nodes along the multi-hop link is already covered by Rel-17/18 specifications and any enhancement is only an optimization.

Based on the discussion in the previous sections we propose the following:
Proposal 1	Only the measurement report sent by the remote UE should be considered for triggering the multi-hop path switch procedure.
Proposal 2	Confirm that the measurement report sent by the first relay UE, intermediate relay UE or the second relay UE does not affect remote UE’s multi-hop path switch procedure as group mobility is not supported.
Proposal 3	For multi-hop i2d and i2i, the intermediate relay UE evaluates adjacent upstream relay link, candidate relay link and Uu-link, where the sidelink measurement report includes at least the information as source L2 ID, serving cell ID, an a sidelink measurement quantity information.
Proposal 4	Do not pursue multi-hop downstream notification of the path switch/handover to trigger relay reselection at the remote UE, reuse Rel-17/18 mechanisms to inform child or parent node.
4	

3GPP TSG-RAN-WG2 Meeting #130	R2-2504360
19th– 23rd May, 2025
Agenda item	:		8.13.4
Source	: 	Sharp
Title	: 	discussion on service continuity for multi-hop relay
Document for	:	Discussion and Decision

Conclusion
In this paper, we made following observations and proposals:
Proposal 1. In scenario B, RAN2 confirms that the UE not in RRC_CONNECTED can be selected as a target relay UE without any effort in RAN2.
Proposal 2. The completion condition of path switching procedure in Rel-17/18 should be reused for all scenarios.
Proposal 3. In scenario A, the legacy Timer T304 is reused.
Proposal 4. In scenario B, C and D, the legacy Timer T420 is reused.
Proposal 5. The PC5 connection between the remote UE and the first relay UE can be released after the remote UE switches from the multi-hop indirect path to direct/single-hop indirect path. The exact timing is up to the remote UE.
Proposal 6. For lossless path switching for UL data, it is up to gNB whether/when the configurations for the remote UE in the first relay UE and the last relay UE on the source path and the PC5 connection between the first relay UE and the last relay UE are released.
Proposal 7. Current measurement reporting event Y1 and Y2 can be reused for scenario C.
Proposal 8. Current measurement reporting event X2, Y2 and Z1 can be reused for scenario D.
Proposal 9. RAN2 considers if the mechanism that relay reselection performed by an intermediate relay UE while keeping PC5-link to a child UE can be applied to the reconfiguration with sync, without supporting service continuity. 
Observation 1. gNB can decide whether the reported first relay UE can reach the gNB since first relay UE contains cellAccessRelatedInfo of serving cell of last relay UE in RRC container included in discovery message.
Proposal 10. The cellIdentity in sl-MeasResultRelay without enhancement can be used for decision whether the candidate first relay UE is connecting with the same gNB.
Proposal 11. Information indicating whether the measurement result is SL-RSRP or SD-RSRP can be included in the measurement report to the gNB as with legacy.
Observation 2. In order to select appropriate path, from the perspective of QoS and radio resource management, gNB needs to know PC5 link quality of the PC5 links, number of hops, and QoS profile for the (potential) remote UE.
Observation 3. gNB already knows number of hops, and QoS profile for the (potential) remote UE.
Observation 4. The greater number of hops there are, the more the quality of each hop affects the delay and the efficiency of radio resource utilization.
Proposal 12. Potential remote UE reports to the gNB the PC5 link qualities of each hops of the path first relay UE belongs or accumulated QoS for the PC5 links (i.e. Achievable PDB). 

3GPP TSG-RAN WG2 Meeting #130		R2-2504524
St.Julians, Malta, 19th – 23rd May 2025		Resubmission of R2-2502420
Source:	vivo
Title:	Discussion on service continuity for scenario C and D
Agenda Item:		8.13.4
Document for:	Discussion and Decision

Conclusion
In this contribution, we discussed the measurement configuration and event definition for scenario C and D. We also discussed the case that whether the target first/intermediate/last relay UE can be the source single-hop U2N relay UE in scenario D. We have the following Observations and Proposals:
For scenario C:
Proposal 1: Event Y1 and Event Y2 are reused in intra-gNB direct to multi-hop indirect path switch, with modifying ‘candidate L2 U2N Relay UE’ to ‘candidate first relay UE’.
Proposal 2: For intra-gNB direct to multi-hop indirect path switch, remote UE evaluates both relay link (for the link between remote UE and candidate first relay UE) and Uu link, where the sidelink relay measurement report shall include at least candidate first relay UE's source L2 ID, serving cell ID and sidelink measurement quantity result.
Proposal 3: Before the candidate first relay UE connects to a remote UE, it can establish itself as a remote UE and follows the legacy measurement configuration and reporting procedures.

For scenario D:
Proposal 4: Event X2, Event Y2 and Event Z1 are reused in intra-gNB single-hop indirect to multi-hop indirect path switch, with modifying ‘candidate L2 U2N Relay UE’ to ‘candidate first relay UE’.
Proposal 5: For intra-gNB single-hop indirect to multi-hop indirect path switch, the remote UE reports serving single-hop relay UE and candidate first relay UE(s), including at least a source L2 ID, serving cell ID, and a sidelink measurement quantity information.
Proposal 6: For scenario D, RAN2 supports the case that the target first/intermediate/last relay UE are all new relay UEs which are not the source single-hop U2N relay UE.
Proposal 7: For scenario D, RAN2 does not specify anything to support the case that that either the target first/intermediate/last relay UE is the source single-hop U2N relay UE.

3GPP TSG-RAN WG2 Meeting #129bis	R2-2502456
China, Wuhan, April 7th – 11th, 2025
Source:	Qualcomm Incorporated 
Title:	Discovery and Relay (re)selection for multi-hop U2N relay
Agenda Item:	8.13.2
Document for:	Discussion and Decision
Introduction & 

Conclusion
Remote UE performs path switching in Scenario C and Scenario D
Remote UE sends measurement report to the gNB when the following conditions are satisfied,
The source link quality is below a threshold, e.g. existing event A2 and Z2.
Remote UE detects candidate multi-hop relay path(s) using relay (re)selection criteria.
Remote UE includes all the relay UE info on the candidate relay path to the gNB in measurement report.
For Model A discovery, Remote UE only treats the relay path on which there is only one intermediate Relay UE as candidate relay path to be reported to the gNB.
Remote UE includes hop number of the candidate relay path into measurement report.
Remote UE can report multiple candidate relay paths to the gNB in measurement report.
Remote UE can report Accumulated QoS for PC5 link on each candidate relay path to gNB in measurement report.
Intermediate Relay UE performs path switching
The intermediate Relay UE can report measurement report UE to gNB for path switching to direct path or indirect path acting as a Remote.
When the intermediate Relay UE performs path switching to direct path or indirect path, the intermediate Relay UE informs the Remote UE via the child intermediate relay UE with release cause 'RRC connection failure'.
When the Remote UE receives notification from the relay UE, the Remote UE should go back to IDLE.