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5G Radio Link Failure Recovery Call Flow

call-flow 5G NR | Radio Recovery | RLF | RRC | Service Continuity

5G Radio Link Failure Recovery is the broader failure-handling path that begins when connected-mode radio continuity is lost badly enough that ordinary connected-mode control is no longer enough.

It joins failure detection, branch selection, reestablishment or fresh setup, and later service restoration into one practical recovery story.

Introduction

RLF recovery is bigger than a single message. It starts before the visible recovery exchange and ends only when the UE has real service again.

That is why this page sits naturally beside Beam Failure Recovery and RRC Reestablishment rather than replacing them.

What Is Radio Link Failure Recovery in Simple Terms?

What starts the procedure: The active radio link becomes unusable.
What the UE and network want to achieve: Recover the fastest valid radio and service path after failure.
What success looks like: The UE chooses the right branch and real service returns with acceptable outage time.
What failure means: Recovery branch selection, context continuity, or post-recovery service continuation breaks down.

Why this procedure matters

Radio link failure recovery is where 5G access resilience becomes measurable. It reveals whether the network can turn severe radio trouble into a short interruption or whether the outage cascades into a long restart.

Quick Fact Sheet

Procedure name	5G Radio Link Failure Recovery
Domain	5G NR connected-mode radio failure handling
Main trigger	The UE or network determines that the active radio link is no longer usable
Start state	UE was connected, but radio continuity has broken down badly enough to threaten the session
End state	The UE either recovers through reestablishment or falls back to fresh access and broader restoration
Main nodes	UE, gNB, optionally AMF and later target nodes
Main protocols	RRC, radio-failure detection, NAS as later recovery continuation
Main success outcome	The failure is recognized quickly and the UE follows the correct next recovery branch
Main failure outcome	Recovery branch selection is wrong, context is lost, or the UE remains out of service too long
Most important messages	RRC Reestablishment Request, RRC Reestablishment, RRC Setup Request
Main specs	TS 38.331, TS 38.300, TS 23.502

5G Radio Link Failure Recovery call flow

Preconditions

The UE was previously in connected mode.
Radio continuity has degraded beyond ordinary connected-mode correction.
The UE can still attempt a valid recovery branch.
Later NAS or service restoration remains possible after radio recovery.

Nodes and Interfaces

Nodes involved

Node	Role in this procedure
UE	Detects that connected-mode continuity is gone and chooses the right next recovery branch.
gNB	May accept reestablishment, reject it, or indirectly force the UE to fall back to fresh access.
AMF	Becomes relevant once the UE must continue into broader service restoration after radio recovery.

Interfaces used

Interface	Path	Role
NR-Uu	UE <-> gNB	Carries the immediate radio recovery attempt after link failure.
N1 and N2	UE/gNB <-> AMF	Carry later recovery continuation if the UE must rebuild higher-layer service after radio recovery.

End-to-End Call Flow

UE                    gNB                    AMF
|== radio link fails ==|                       |
|-- Reestablishment Request? ->|               |
|<- Reestablishment -----------|               |
|   or fallback to Setup       |               |
|-- later service restoration ---------------->|

Major Phases

Phase	What happens
1. Radio failure detection	The connection degrades beyond normal connected-mode recovery and is treated as a real radio link failure.
2. Recovery branch selection	The UE decides whether it can attempt RRC Reestablishment or must fall back to fresh setup.
3. Radio recovery attempt	The network either restores the connection through reestablishment or leaves the UE to perform new access.
4. Higher-layer continuation	After radio recovery, the UE still may need service restoration, security refresh, or session continuity work.

Step-by-Step Breakdown

UE recognizes that connected mode is no longer viable

Sender -> receiver: UE radio failure detection

Message(s): RLF detection, failed handover continuation, or severe beam or signal collapse

Purpose: Move from ordinary connected-mode handling into explicit failure recovery logic.

State or context change: The connection is no longer trustworthy enough for normal traffic continuation.

Note: The most valuable context is often the few seconds before this point, not only the recovery branch itself.

UE decides whether reestablishment is possible

Sender -> receiver: UE recovery logic

Message(s): RRC Reestablishment Request or fresh setup path

Purpose: Choose the least disruptive valid recovery option based on surviving context.

State or context change: The failure branches into reestablishment or new access.

Note: A wrong branch choice or stale context can waste time and deepen the outage.

Network accepts reestablishment or forces fallback

Sender -> receiver: UE <-> gNB

Message(s): RRC Reestablishment or later RRC Setup Request

Purpose: Recover the radio link in the quickest valid way.

State or context change: The UE either regains connected mode with preserved context or starts over with fresh access.

Note: The presence or absence of usable context is the main divider between graceful and disruptive recovery.

UE continues into broader service restoration

Sender -> receiver: UE -> gNB -> AMF

Message(s): RRC Reestablishment Complete, Setup Complete, Service Request, or Registration Request

Purpose: Restore actual service after the radio problem is under control.

State or context change: The recovery shifts from pure radio continuity into end-to-end service continuity.

Note: Do not mark the case as solved until traffic or signaling really resumes.

Important Messages in This Flow

Message	Protocol	Direction	Purpose in this procedure	What to inspect briefly
RRC Reestablishment Request	RRC	UE -> gNB	Starts the preferred failure-recovery branch when enough context survives.	Inspect cause, short identity, and whether the target cell is appropriate.
RRC Reestablishment	RRC	gNB -> UE	Restores the radio leg if recovery is accepted.	Inspect whether the network really had usable context for the UE.
RRC Setup Request	RRC	UE -> gNB	Represents the fallback to fresh access if reestablishment is not viable.	Use it to confirm that the trace shifted from recovery into restart.

Important Parameters to Inspect

Parameter	What it is	Where it appears	Why it matters	Common issues
Failure cause context	What triggered the RLF path: beam collapse, handover failure, interference, or rapid signal loss.	Pre-failure trace window	Explains why the link failed and what kind of fix is realistic.	Without cause context, teams only treat symptoms.
Surviving context validity	Whether the UE still has enough context for reestablishment.	Recovery branch selection	Determines whether quick recovery is possible.	Stale context leads to failed reestablishment and longer outage.
Recovery timing	How quickly the UE moves from failure detection into a valid branch.	RLF timeline	Directly affects outage duration.	Delayed branch selection wastes the limited recovery window.
Target or serving cell suitability	Whether the chosen cell can support recovery.	Reestablishment or fresh access attempt	A good branch still fails on a bad cell choice.	Poor cell choice can look like generic radio failure.
Post-recovery service continuation	What happens after the radio link comes back.	Later NAS and user-plane behavior	Confirms whether the user experience really recovered.	Radio recovery alone may not restore traffic.

Success Criteria

The failure cause is understood early enough to guide the right branch.
Reestablishment is used when context is still valid, or fresh setup is used quickly when it is not.
The recovery cell and access path are suitable.
Service continuity really returns after radio recovery.

Common Failures and Troubleshooting

Symptom	Likely cause	Where to inspect	Relevant message(s)	Relevant interface(s)	Likely next step
Reestablishment is attempted but never completes	The surviving context was insufficient or the chosen recovery cell was unsuitable.	Reestablishment cause, identity, and target-cell viability.	RRC Reestablishment Request, RRC Reestablishment	NR-Uu	This is a core RLF recovery failure branch.
UE falls back to setup but service still takes too long	The radio failure forced a full restart and later higher-layer restoration also struggled.	Fallback timing and post-setup NAS continuation.	RRC Setup Request, Setup Complete, Service Request	NR-Uu, N1, N2	Treat this as a longer outage chain, not one isolated event.
RLF is blamed on the wrong domain	The visible failure happened in radio recovery, but the root cause was earlier beam trouble or poor mobility decisions.	The trace window before the explicit failure declaration.	Measurements and earlier reconfiguration	NR-Uu	Look backward before optimizing only the recovery branch.
Radio recovers but user traffic remains broken	The access leg returned, but session, security, or service restoration still failed.	Post-recovery NAS and user-plane behavior.	Reestablishment Complete, Setup Complete, Service Request	N1, N2, N3	Do not stop at radio success.

What to Check in Logs and Traces

Look at the seconds before RLF, not only the recovery messages.
Confirm whether reestablishment was truly viable or whether the UE correctly needed fresh setup.
Measure the gap between failure detection and restored useful service.
If the radio recovers but traffic does not, keep following NAS and session continuity.

Related sub-procedures

Related message reference pages

Related troubleshooting pages

FAQ

What is 5G Radio Link Failure Recovery?

It is the broader recovery handling used when the active connected-mode radio link breaks down and the UE must restore service through reestablishment or fresh access.

Is it the same as RRC Reestablishment?

No. Reestablishment is one important branch inside the broader RLF recovery story.

What commonly causes RLF?

Beam collapse, rapid signal degradation, interference, failed mobility execution, or severe radio instability can all lead to it.

What should I inspect first?

Start with the pre-failure radio trend, then identify whether reestablishment or fresh setup was the right branch.

When is the case really solved?

Only when radio recovery leads to real service continuity, not just when a recovery message appears.