NAS 5G UE to AMF 3GPP TS 24.501

5G NAS - Registration Complete

Registration Complete is the UE-to-AMF NAS message used to confirm that the UE has accepted the registration context returned by the network.

Message Fact Sheet

Protocol	nas	Network	5g
Spec	3GPP TS 24.501	Spec Section	8.2.8
Direction	UE to AMF	Message Type	5GMM signaling

Full message name	5G NAS - Registration Complete
Protocol	NAS
Technology	5G
Direction	UE to AMF
Interface	N1
Signaling bearer / channel	NAS signaling / Dedicated NAS message, commonly transported via UL Information Transfer on the access side
Typical trigger	Sent after the UE receives and accepts Registration Accept.
Main purpose	Closes the successful registration exchange and confirms that the UE has stored or applied the context returned in Registration Accept.
Main specification	3GPP TS 24.501, 8.2.8
Release added	Release 15
Procedures where used	5G Initial Registration, Mobility Registration Update
Related timers	T3550
Related cause values	Registration Complete does not carry reject causes

What is Registration Complete in simple terms?

Registration Complete is the UE-to-AMF NAS message used to confirm that the UE has accepted the registration context returned by the network.

Closes the successful registration exchange and confirms that the UE has stored or applied the context returned in Registration Accept.

Why this message matters

Registration Complete is the UE saying the registration success message was received and accepted.

Where this message appears in the call flow

5G Initial Registration

Call flow position: Final UE confirmation after Registration Accept in a successful registration sequence.

Typical state: UE is entering 5GMM-REGISTERED state.

Preconditions:

The UE has received Registration Accept.
Returned registration context has been parsed and accepted.

Next likely message: Normal service activity or optional follow-on NAS procedures

Call flow position

Previous message(s): Registration Accept, DL Information Transfer

Next message(s): Configuration Update Command, PDU Session Establishment Request, Normal registered-state service behavior

Message direction and transport

Sender and receiver: UE to AMF

Interface: N1

Domain: Core-side mobility management message with radio-side transport dependency

Signaling bearer: NAS signaling

Logical channel: Dedicated NAS message, commonly transported via UL Information Transfer on the access side

Transport / encapsulation: NAS 5GS message carried end-to-end between UE and AMF

Security context: Normally sent after NAS security activation, so engineers usually expect integrity protection and often ciphering.

Message Structure Overview

Registration Complete is usually short and procedural.
Its engineering value is less about payload size and more about confirming that the UE accepted the Registration Accept context without error.
When this message is missing, engineers often look backward at Registration Accept handling rather than forward at later NAS procedures.

Structure Syntax

This message is not typically analyzed as ASN.1 on the wire. Engineers usually inspect it as a NAS or protocol field decode rather than an ASN.1 tree.

Registration Complete is a NAS 24.501 message, not an ASN.1-defined message.

Decoded Message Dump

Registration Complete
  Extended Protocol Discriminator: 5G Mobility Management
  Security Header Type: Integrity protected and ciphered
  Message Type: Registration Complete

How to read this dump

The first check is that the message follows Registration Accept quickly and under the expected NAS security header.
If optional containers are present, confirm they match roaming or policy context.

Important Information Elements

IE	Required	Description
`SOR transparent container`	Optional	Optional container used when steering of roaming information must be returned by the UE.

Detailed field explanation

`SOR transparent container`

Optional container used when steering of roaming information must be returned by the UE.

Presence: Optional

What to check in logs and traces

Verify Registration Complete is present after Registration Accept.
Check the NAS security header and sequence progression.
If the message is missing, inspect whether the UE rejected or failed to process Registration Accept.
Correlate the message with the AMF clearing T3550 and moving the UE into normal registered state.

Common Issues and Troubleshooting

Registration Accept is present but Registration Complete is missing.

Likely cause: The UE may have failed while processing the returned registration context or the uplink transport path may have failed.

What to inspect: Check Registration Accept contents, UL Information Transfer, RRC stability, and NAS integrity state.

Next step: Compare with a known-good trace and verify whether the UE resets, sends status, or starts a new registration.

Registration repeats even after apparent success.

Likely cause: The network may not have received Registration Complete, or the UE may not have retained the returned context.

What to inspect: Check uplink delivery of Registration Complete and the next AMF-side state transition.

Next step: Correlate with NAS retransmission timers and subsequent Registration Request attempts.

Detailed explanation

5G NAS - Registration Complete Explained

Registration Complete is the final UE-side confirmation in a successful 5G registration exchange. The network has already accepted registration. This message simply confirms that the UE received that result and accepted the returned context.

What is Registration Complete in simple terms?

The UE sends Registration Complete after it receives Registration Accept.
In simple terms: the network says registration worked, and the UE replies that it successfully received and applied that context.

Why this message matters

It matters because a registration flow can still fail operationally if the AMF never receives the UE’s final confirmation. A trace that ends at Registration Accept is not always enough to prove that the registration procedure truly completed.

Where this message appears in the call flow

UE                              gNB / AMF
|<-- Registration Accept --------|
|--- Registration Complete ----->|
|   UE is now in registered use  |

This message sits at the end of successful registration and before normal service behavior.

Transport characteristics

sender: UE
receiver: AMF
interface: N1
access-side transport: typically UL Information Transfer
protection: normally sent under active NAS security

What Registration Complete means operationally

Operationally, this message tells the AMF that the UE successfully processed the context returned in Registration Accept. It is small, but it confirms that the registration procedure really reached its final UE-side completion point.

That matters because a trace that stops at Registration Accept can still be misleading. If Registration Complete never arrives, the AMF may keep retry logic active or the procedure may repeat later even though registration appeared to succeed.

Important Information Elements

IE	Why it matters
`SOR transparent container`	Optional but useful in roaming-related scenarios.

Example message dump

Registration Complete
  Extended Protocol Discriminator: 5G Mobility Management
  Security Header Type: Integrity protected and ciphered
  Message Type: Registration Complete

How to read this dump

Check that the NAS protection state looks correct.
Confirm it appears directly after Registration Accept.
If it is missing, the problem is often in UE context handling or uplink delivery rather than in the AMF decision itself.

What to check in logs

verify that Registration Accept arrived first and carried valid context
confirm the UE sends Registration Complete without long delay
inspect uplink NAS transport and RRC stability if the message is missing
correlate the message with the AMF clearing T3550 and moving the UE into steady registered behavior

FAQ

What does Registration Complete do in 5G?

It confirms that the UE accepted the context returned in Registration Accept and completes the successful registration exchange.

Who sends Registration Complete?

The UE sends it to the AMF over NAS after processing Registration Accept.

Is Registration Complete protected?

In most successful registration flows, yes. It is normally sent after NAS security is active.

Summary

Registration Complete is the UE-to-AMF NAS message used to confirm that the UE has accepted the registration context returned by the network.

Advanced Engineer Notes

This message is small, but its absence often explains why a registration that looked successful still collapses into repetition.
Engineers should treat missing Registration Complete as a signaling-completion issue, not automatically as an AMF rejection problem.

Related message pages

Related Procedures

5G Initial Registration

Related Tools

Use This Reference in Practice

Decode this message with the 3GPP Decoder, inspect the related message database, or open the matching call flow to see where this signaling step fits in the full procedure.