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5G Local Breakout Roaming Registration Call Flow

call-flow 5G NR | Roaming | Local Breakout | NAS | Registration

5G Local Breakout Roaming Registration is the roaming registration path used when the visited network is expected to support local service continuity afterward.

It combines standard roaming validation with the service model assumptions needed for later local-breakout data service.

Introduction

This procedure should be read as the registration foundation for a local-breakout roaming service model, not as the PDU session establishment itself.

In practice, the most useful checks are the visited PLMN, subscriber entitlement, accepted service restrictions, and whether the returned context really supports the intended follow-up behavior.

What Is Local Breakout Roaming Registration in Simple Terms?

What starts the procedure: A roaming UE needs 5GS registration in a visited PLMN with local-breakout-capable service expectations.
What the UE and network want to achieve: Complete secure roaming registration and prepare for visited-network service continuity.
What success looks like: The UE registers cleanly and can move on to the intended local-breakout session workflow.
What failure means: Roaming entitlement or service-model alignment is not sufficient for the intended outcome.

Why this procedure matters

Local-breakout roaming problems are often misdiagnosed because teams jump straight to session setup. A correct registration foundation is what makes the later roaming data path understandable.

Quick Fact Sheet

Procedure name	5G Local Breakout Roaming Registration
Domain	5G roaming registration where visited-network service breakout is expected after registration
Main trigger	A roaming UE registers in a visited PLMN that supports local breakout service treatment
Start state	UE is in a visited network and needs valid roaming registration before local service breakout can be used
End state	UE is registered and prepared for visited-network service continuity under the local-breakout model
Main nodes	UE, visited gNB, visited AMF, home subscriber functions, visited policy and session functions
Main protocols	RRC, NAS, NGAP, roaming subscriber signaling, authentication, visited policy coordination
Main success outcome	The UE completes roaming registration and is ready for visited-network service breakout
Main failure outcome	Registration succeeds only partially or fails because local-breakout policy, roaming entitlement, or security cannot be aligned
Most important messages	Registration Request, Authentication Request/Response, Security Mode, Registration Accept, Registration Complete
Main specs	TS 23.501, TS 23.502, TS 24.501, TS 29.510 family

5G Local Breakout Roaming Registration call flow

Preconditions

The UE has coverage in a visited PLMN.
Home and visited networks support the relevant roaming agreement.
The UE can present valid identity context for roaming.
The visited network has policy and session logic for the intended service model.

Nodes and Interfaces

Nodes involved

Node	Role in this procedure
UE	Starts the roaming registration and later relies on the returned context for local-breakout-capable service.
Visited gNB	Provides the access path for registration in the visited PLMN.
Visited AMF	Coordinates the roaming registration from the visited-core side.
Home subscriber functions	Confirm subscriber identity and entitlement for roaming.
Visited policy and session functions	Shape how later local-breakout service may be offered after registration.

Interfaces used

Interface	Path	Role
NR-Uu	UE <-> visited gNB	Carries the radio path for the roaming registration attempt.
N1	UE <-> visited AMF	Carries registration, security, and acceptance signaling.
N2	visited gNB <-> visited AMF	Relays access-side context and NAS messages.
Roaming subscriber interfaces	visited core <-> home core	Carry subscriber and authentication validation.
Visited policy interfaces	visited core internal control	Prepare the service model that follows registration.

End-to-End Call Flow

UE             visited gNB         visited AMF        home / visited functions
|                  |                  |                    |
|-- Registration Request -----------> |                    |
|                  |----------------->|-- validation ------>|
|                  |                  |<-- entitlement ------|
|<-- Authentication / Security ------|                    |
|<-- Registration Accept ------------|                    |
|-- Registration Complete ---------->|                    |
|==== registration ready for local-breakout follow-up ===>|

Major Phases

Phase	What happens
1. Visited-network access	The UE selects a visited PLMN and prepares to register.
2. Roaming registration start	The UE sends Registration Request through the visited access network.
3. Home-side validation plus visited policy alignment	Subscriber entitlement is checked while the visited network prepares the local-breakout-capable service model.
4. Security and accept	The UE completes authentication and receives Registration Accept.
5. Completion and local-breakout readiness	The UE returns Registration Complete and can proceed to visited-network service setup.

Step-by-Step Breakdown

The UE enters a visited PLMN that supports local breakout

Sender -> receiver: UE -> visited gNB

Message(s): PLMN selection and access establishment

Purpose: Create the access path for a roaming registration that will later support visited-network data continuity.

State or context change: The UE prepares to register in a foreign network with a specific roaming service model in mind.

Note: This page focuses on the registration side of local breakout, not the later PDU session setup itself.

The UE sends Registration Request

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

Message(s): Registration Request

Purpose: Start the roaming registration and expose identity plus requested context.

State or context change: The visited AMF creates a roaming registration transaction.

Note: Requested slices and service expectations matter because they affect later local-breakout feasibility.

Visited and home sides align on entitlement

Sender -> receiver: Visited AMF <-> home subscriber functions

Message(s): Subscriber validation and authentication coordination

Purpose: Confirm the subscriber may roam and that the registration can progress.

State or context change: The UE moves from provisional access toward authenticated roaming state.

Note: The local-breakout model still depends on basic roaming entitlement from the home side.

Visited network prepares the post-registration service model

Sender -> receiver: Visited AMF <-> visited policy and session functions

Message(s): Policy alignment for later local breakout

Purpose: Make sure the visited network can later offer local continuity where permitted.

State or context change: The returned registration context becomes suitable for local-breakout service follow-up.

Note: Registration may succeed even if later local-breakout session setup remains restricted. Keep those two outcomes separate.

The UE completes registration

Sender -> receiver: Visited AMF <-> UE

Message(s): Authentication Request, Registration Accept, Registration Complete

Purpose: Finish secure roaming registration so the UE can proceed to visited-network data service.

State or context change: The UE becomes stable in the local-breakout-capable roaming state.

Note: Later session success depends on this registration context, but does not prove local breakout by itself.

Important Messages in This Flow

Message	Protocol	Direction	Purpose in this procedure	What to inspect briefly
Registration Request	NAS	UE -> visited AMF	Starts the local-breakout-capable roaming registration.	Inspect identity, requested context, and slice expectations.
Authentication Request	NAS	Network -> UE	Confirms that subscriber validation is progressing.	Useful for proving the process reached secure roaming treatment.
Registration Accept	NAS	visited AMF -> UE	Returns the accepted roaming context.	Check what service and slice context the UE is actually allowed to use.
Registration Complete	NAS	UE -> visited AMF	Finalizes the registration transaction.	Needed before later local-breakout service setup can be read cleanly.

Important Parameters to Inspect

Parameter	What it is	Where it appears	Why it matters	Common issues
Visited PLMN and TAC	Location where local-breakout-capable roaming registration is attempted.	Access and registration context	Defines the roaming environment and policy domain.	Wrong visited context invalidates the analysis.
UE identity	Subscriber identity used for roaming.	Registration Request	Must correlate cleanly with home-side validation.	Identity mismatch causes misleading reject behavior.
Allowed NSSAI / visited restrictions	What the UE may actually use after registration.	Registration Accept	Important for later local-breakout session feasibility.	Registration success may still hide later service limits.
Roaming entitlement	Home-side permission for the roaming attempt.	Subscriber validation path	Separates authorization failure from later session failure.	A missing entitlement blocks everything upstream.
Visited service model readiness	Whether the visited network is prepared to support the intended post-registration continuity model.	Visited policy context	Explains the difference between generic roaming success and useful local breakout readiness.	Often misunderstood in field troubleshooting.

Success Criteria

The roaming registration completes cleanly in the visited network.
The home side authorizes the subscriber for roaming.
The accepted context reflects the intended visited-network service limits.
The UE is ready for later local-breakout PDU session procedures.

Common Failures and Troubleshooting

Symptom	Likely cause	Where to inspect	Relevant message(s)	Relevant interface(s)	Likely next step
Registration succeeds but local-breakout service later fails	Registration was valid, but the visited-network service model is still too restricted.	Allowed NSSAI and visited restrictions.	Registration Accept	Policy and session follow-up	Keep registration success separate from session continuity success.
Roaming validation fails before Registration Accept	Subscriber entitlement or authentication did not complete cleanly.	Identity and authentication path.	Registration Request / Authentication	N1, roaming interfaces	Start with cross-network entitlement.
The UE never finalizes registration	The Accept was not fully adopted or the completion leg failed.	Accept-to-Complete path and UE state.	Registration Complete	N1, NR-Uu	This leaves confusing half-open roaming context.
Visited-network restrictions are misread as generic roaming failure	The UE is registered, but not with the service breadth expected by the operator or tester.	Accepted restrictions and later service attempts.	Registration Accept	Policy	A clean registration trace does not imply unrestricted local breakout.

Related sub-procedures

Related message reference pages

Related troubleshooting pages

FAQ

What is Local Breakout Roaming Registration?

It is the roaming registration path used when the UE is expected to continue later service through a visited-network breakout model.

Does this page mean the PDU session is already locally broken out?

No. This page covers the registration context that makes later local-breakout service possible.

What proves success?

Registration Accept, Registration Complete, and a roaming context suitable for the intended visited-network service model.

What should I inspect first?

Start with visited PLMN, identity, roaming entitlement, and the accepted service restrictions.

Why can later service still fail after successful registration?

Because registration and local-breakout session establishment are related but separate procedures.