NAS 5G UE to network 3GPP TS 24.501

5G NAS - Relay Authentication Response

Relay Authentication Response is the NAS message the UE or relay participant sends back after Relay Authentication Request to return the relay-specific authentication result information.

Message Fact Sheet

Protocol	nas	Network	5g
Spec	3GPP TS 24.501	Spec Section	8.2.38
Direction	UE to network	Message Type	5GMM signaling

Full message name	5G NAS - Relay Authentication Response
Protocol	NAS
Technology	5G
Direction	UE to network
Interface	N1
Signaling bearer / channel	NAS signaling / Dedicated NAS message, transported over the existing NAS path
Typical trigger	Sent after the UE or relay participant successfully processes Relay Authentication Request and produces the required relay-authentication response.
Main purpose	Returns the relay authentication response parameters so the relay security procedure can continue or conclude.
Main specification	3GPP TS 24.501, 8.2.38
Release added	Release 17
Procedures where used	Relay authentication procedure, Relay security handling, ProSe relay context
Related timers	Procedure dependent
Related cause values	Relay authentication response parameter semantics

What is Relay Authentication Response in simple terms?

Relay Authentication Response is the NAS message the UE or relay participant sends back after Relay Authentication Request to return the relay-specific authentication result information.

Returns the relay authentication response parameters so the relay security procedure can continue or conclude.

Why this message matters

Relay Authentication Response is the relay participant answering the network's relay authentication challenge.

Where this message appears in the call flow

Relay Authentication Procedure

Call flow position: UE response step after Relay Authentication Request.

Typical state: The relay-capable context exists and the relay participant is returning authentication response data.

Preconditions:

Relay Authentication Request was received.
The UE or relay participant could process the relay authentication challenge.

Next likely message: Relay-specific continuation or procedure outcome handling

ProSe Relay Security Handling

Call flow position: Authentication response step in the relay-specific security exchange.

Typical state: The relay authentication branch is returning challenge-response data to the network.

Preconditions:

Relay transaction context exists.

Next likely message: Relay-specific continuation

Call flow position

Previous message(s): Relay Authentication Request, Relay Key Accept

Next message(s): Relay-specific procedure continuation, Relay procedure success or failure handling

Message direction and transport

Sender and receiver: UE to network

Interface: N1

Domain: Core-side mobility management signaling with relay-specific security context

Signaling bearer: NAS signaling

Logical channel: Dedicated NAS message, transported over the existing NAS path

Transport / encapsulation: NAS 5GS message carried end-to-end between the UE-side relay participant and the network NAS entity

Security context: This message belongs to the relay-authentication branch, so it should be interpreted together with the earlier Relay Authentication Request, relay transaction identity, and any later relay-procedure outcome.

Message Structure Overview

Relay Authentication Response is a specialized NAS relay-security response message rather than a mainstream authentication response used in ordinary registration.
In trace analysis, engineers usually inspect the relay transaction identity first and then the relay authentication response parameters that drive the network's next decision.

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.

Relay Authentication Response follows NAS 24.501 IE structure and is not an ASN.1 message.

Decoded Message Dump

Relay Authentication Response
  Extended Protocol Discriminator: 5G Mobility Management
  Security Header Type: Integrity protected and ciphered
  Message Type: Relay Authentication Response
  ProSe Relay Transaction Identity: 7
  Relay Authentication Response Parameters: 0xa14b77c2...

How to read this dump

The message is best read as a relay-security response whose value comes from the relay transaction identity and authentication response parameters.
The next useful check is what relay-specific procedure step or outcome follows this response.

Important Information Elements

IE	Required	Description
`ProSe relay transaction identity`	Yes	Identifies the relay-authentication transaction so the response can be matched with the earlier request.
`Relay authentication response parameters`	Yes	Carries the relay-specific response data produced after processing the authentication challenge.

Detailed field explanation

`ProSe relay transaction identity`

Identifies the relay-authentication transaction so the response can be matched with the earlier request.

Presence: Required

`Relay authentication response parameters`

Carries the relay-specific response data produced after processing the authentication challenge.

Presence: Required

What to check in logs and traces

Confirm the message directly follows Relay Authentication Request.
Inspect the ProSe relay transaction identity and match it to the request.
Check the relay authentication response parameters.
Look for the next relay-specific procedure outcome or continuation.

Common Issues and Troubleshooting

Relay Authentication Response is sent but the relay procedure still fails.

Likely cause: The challenge-response exchange may have completed, but the network did not accept the returned relay authentication data.

What to inspect: Check the relay transaction identity, the response parameters, and the next relay-specific network decision.

Next step: Correlate the response with the earlier Relay Authentication Request and compare against a known-good relay trace.

Relay Authentication Request is visible but no Relay Authentication Response follows.

Likely cause: The UE or relay participant may not have processed the challenge correctly or the uplink relay-authentication response was not delivered.

What to inspect: Check UE-side processing, lower-layer delivery, and relay transaction correlation.

Next step: Treat the issue as a relay-authentication branch failure rather than a general NAS connectivity problem.

Detailed explanation

5G NAS - Relay Authentication Response Explained

Relay Authentication Response is the UE-side reply to Relay Authentication Request. It carries the relay-specific authentication response data needed for the network to continue or conclude the relay security procedure.

For beginners, the simple meaning is: the relay participant is answering the network’s relay authentication challenge.
For engineers, the key point is that this message belongs to the specialized relay authentication branch, not to ordinary 5GMM authentication.

What is Relay Authentication Response in simple terms?

The network sent Relay Authentication Request with relay-specific challenge information. The UE or relay participant processed that challenge and returned the result in Relay Authentication Response.

Why Relay Authentication Response matters

This message matters because it closes the challenge-response half of the relay authentication step. If it is missing, the relay branch stalls. If it is present, engineers can move on to the network’s next decision instead of staying on the challenge itself.

The most useful practical checks are:

whether the relay transaction identity matches the request
what relay authentication response parameters were returned
what relay-specific step follows next

Where Relay Authentication Response appears in the call flow

UE / Relay Participant            Network
|<-- Relay Authentication Request--|
|--- Relay Authentication Response>|
|<-- Relay-specific continuation --|

It is best interpreted as part of relay authentication handling rather than as part of ordinary registration signaling.

Transport characteristics

Direction: UE to network
Interface: N1
Transport on access side: carried over the existing NAS path
Security expectation: normally tied to an already established protected relay-capable NAS context

What Relay Authentication Response means operationally

Operationally, Relay Authentication Response tells engineers that the relay authentication challenge has been answered and that the network now has enough data to decide the next relay-specific step.

That means the first practical questions are:

which relay transaction this response belongs to
what response parameters were returned
how the network reacts next

Important Information Elements

IE	Why it matters
`ProSe relay transaction identity`	Ties the response to a specific earlier relay authentication request.
`Relay authentication response parameters`	Carries the response data that the network evaluates next.

Example message dump

Relay Authentication Response
  Extended Protocol Discriminator: 5G Mobility Management
  Security Header Type: Integrity protected and ciphered
  Message Type: Relay Authentication Response
  ProSe Relay Transaction Identity: 7
  Relay Authentication Response Parameters: 0xa14b77c2...

How to read this dump

Start with the relay transaction identity.
Then inspect the relay authentication response parameters.
After that, move directly to the next relay-specific network step, because the response is mainly valuable as part of the relay challenge-response pair.

What to check in logs

verify that the message follows the correct Relay Authentication Request
inspect the relay transaction identity
check the relay authentication response parameters carefully
correlate the response with the next relay-specific outcome

FAQ

What does Relay Authentication Response do in 5G?

It returns the relay-specific authentication response information after Relay Authentication Request.

Is Relay Authentication Response the same as normal Authentication Response?

No. The normal Authentication Response belongs to mainstream 5GMM authentication, while Relay Authentication Response belongs to the specialized relay-security branch.

What should engineers inspect first?

Start with the relay transaction identity and the relay authentication response parameters.

Summary

Relay Authentication Response is the NAS message the UE or relay participant sends back after Relay Authentication Request to return the relay-specific authentication result information.

Advanced Engineer Notes

This is a niche Release 17 relay-security response message, so most engineering value comes from correct relay-context correlation rather than from the outer NAS wrapper alone.
If this message is present and well formed, the next troubleshooting focus usually moves to the network's interpretation of the returned relay authentication data.

Related message pages

Related Procedures

Relay Authentication Procedure

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.