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LTE Remote UE Relay Procedure Call Flow

call-flow LTE | Remote UE Relay | NAS

LTE Remote UE Relay Procedure is the relay-related status branch where the remote UE state is exposed through NAS reporting rather than through ordinary LTE-only or generic sidelink-only signaling.

The practical anchors are Remote UE Report and Remote UE Report Response, which together define the remote UE status exchange.

Introduction

This page is most useful when the relay question is centered on remote UE status rather than on the relay-capable UE sidelink branch. The remote UE report and its response are the main facts that explain what the network knew and acknowledged.

Use it when the trace contains the Remote UE Report family and the main question is whether the remote UE relay branch was reported and handled correctly.

What Is LTE Remote UE Relay Procedure in Simple Terms?

What starts the procedure: The network needs the current remote UE relay status from the UE side.
What the UE and network want to achieve: A clear remote UE status view that can be acknowledged and used in later relay handling.
What success looks like: Remote UE Report is sent, the response arrives, and later behavior matches the reported state.
What failure means: The report is missing, not acknowledged, or later handling does not follow the reported status.

Why this procedure matters

Remote UE relay traces are often unclear because the relay story is split across different branches. This page keeps the focus on the NAS status exchange that shows what remote UE state the network actually received.

Quick Fact Sheet

Procedure name	LTE Remote UE Relay Procedure
Domain	Remote UE relay status handling
Main trigger	Need to expose or refresh remote UE relay status
Start state	A relay-related branch exists and remote UE status matters
End state	The network has the remote UE status and has acknowledged it
Main nodes	UE, network side
Main protocols	NAS
Main success outcome	Remote UE status is visible and later handling matches it
Main failure outcome	Remote UE relay handling uses missing or stale status
Most important messages	Remote UE Report, Remote UE Report Response
Main specs	TS 24.301

LTE Remote UE Relay Procedure Call Flow — Click the diagram to open the full-size in a new tab.

Preconditions

A remote UE relay branch is relevant in the trace.
The UE can send the remote UE status to the network side.
The trace includes the report and later response window.

Nodes and Interfaces

Nodes involved

Node	Role in this procedure
UE	Sends the remote UE status and reads the network acknowledgement.
Network side	Receives the remote UE status and returns the response.
Remote UE branch context	Represents the relay-related status branch built around the NAS report exchange.

Interfaces used

Interface	Path	Role
NAS	UE <-> Network side	Carries the remote UE status report and response branch.
LTE control path	UE <-> network side	Carries the wider LTE context around the NAS relay status exchange.

End-to-End Call Flow

UE                     Network side
|--Remote UE Report---->|
|<-Remote UE Report Resp-|
|==== later relay handling ===>|

Major Phases

Phase	What happens
1. Need remote UE visibility	The network reaches a point where remote UE status matters.
2. Report the remote UE state	The UE sends the current relay-related status over NAS.
3. Acknowledge the report	The network returns the response to the UE.
4. Continue with the relay branch	Later relay handling should now reflect the reported remote UE state.

Step-by-Step Breakdown

Send the status report

Sender -> receiver: UE -> Network side

Message(s): Remote UE Report

Purpose: Expose the current remote UE relay status.

State or context change: The network now has the key relay-related status needed for later action.

Note: This is the main proof of what the UE actually told the network.

Receive the acknowledgement

Sender -> receiver: Network side -> UE

Message(s): Remote UE Report Response

Purpose: Confirm receipt and handling of the remote UE status report.

State or context change: The report exchange is now complete from the NAS point of view.

Note: If the response is missing, later network assumptions should be treated carefully.

Read the report into later branch handling

Sender -> receiver: Network side

Message(s): Later relay-aware decision

Purpose: Use the reported remote UE status in the next relay branch.

State or context change: Later handling is now working from an explicit remote UE status view.

Note: This explains whether the network had the right relay-state view before the next action.

Validate later behavior

Sender -> receiver: UE <-> Network side

Message(s): Relay continuation after the report exchange

Purpose: Check whether later branch behavior fits the report and response pair.

State or context change: The remote UE relay branch is now complete enough to evaluate.

Note: This is where report accuracy and decision accuracy should be separated.

Important Messages

Message	Protocol	Direction	Purpose in this procedure	What to inspect briefly
Remote UE Report	NAS	UE -> Network side	Carries the current remote UE relay status.	Check the reported status itself and the branch context immediately around it.
Remote UE Report Response	NAS	Network side -> UE	Acknowledges the remote UE status exchange.	Check whether the report was actually acknowledged before later behavior is judged.
Sidelink UE Information r12	RRC	UE -> eNB	Useful companion reference when the relay trace also includes a relay-capable sidelink branch.	Check whether the trace is mixing remote UE NAS status with relay-capable UE sidelink reporting.

Important Parameters to Inspect

Parameter	What it is	Where it appears	Why it matters	Common issues
Reported remote UE status	The actual relay-related status sent by the UE.	Remote UE Report	It is the core fact later handling should use.	Later behavior is judged without checking the reported state itself.
Response presence	Whether the network acknowledged the report.	Remote UE Report Response	Useful for proving the report exchange really completed.	The later branch is treated as report-aware even though the exchange never completed cleanly.
NAS-versus-RRC branch identity	Whether the trace question is in the NAS remote UE branch or the RRC relay-capable UE branch.	Whole procedure window	Prevents remote UE status analysis from being mixed with sidelink report analysis.	The wrong relay message family is being used to explain the behavior.
Later action alignment	Whether the next relay branch matches the reported status.	Post-response continuation	Separates status reporting problems from later decision problems.	The report is correct, but the network still follows stale assumptions.
Exchange timing	How close the report and response are to the later relay action.	Around the report window	Useful when several relay-related updates appear in one trace.	The wrong report instance is matched to the later behavior.

Successful Completion

Success means the remote UE status is reported, acknowledged, and then reflected correctly in later relay handling.

Common Failures and Troubleshooting

Symptom	Likely cause	Where to inspect	Relevant message(s)	Relevant interface(s)	Likely next step
Later relay behavior does not match the reported remote UE state	The network may be using stale status or the wrong relay branch context.	Remote UE Report, its response, and the next relay action together.	Remote UE Report, Remote UE Report Response	NAS	Align one report-response pair with one later action before diagnosing the branch logic.
The relay trace is unclear because multiple relay-related message families are present	The trace may mix Remote UE Report with sidelink relay signaling.	NAS report exchange and nearby sidelink report windows.	Remote UE Report, Sidelink UE Information r12	NAS, RRC	Separate remote UE status handling from relay-capable UE reporting first.

What to Check in Logs and Traces

Use the Remote UE Report and Remote UE Report Response pair as one exchange.
Keep NAS remote UE status handling separate from RRC sidelink relay reporting.
Check whether later relay behavior follows the exact reported state.

Related sub-procedures

Related message reference pages

Related troubleshooting pages

Notes

Use this page when the main trace anchors are the NAS remote UE status messages. If the main anchors are the sidelink UE report messages, start from the sidelink relay UE page instead.

FAQ

What is the LTE Remote UE Relay Procedure?

It is the relay-related NAS status branch where the UE reports remote UE state and the network acknowledges it.

Which messages define the procedure?

Remote UE Report and Remote UE Report Response are the main anchors.