NAS 5G UE to network 3GPP TS 24.501

5G NAS - Relay Key Request

Relay Key Request is the NAS message used to request relay-related keying material so the relay security procedure can continue in a 5G relay or ProSe relay context.

Message Fact Sheet

Protocol	nas	Network	5g
Spec	3GPP TS 24.501	Spec Section	8.2.34
Direction	UE to network	Message Type	5GMM signaling

Full message name	5G NAS - Relay Key Request
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 when the UE needs relay key material for a relay-related security procedure and the network must provide the corresponding response.
Main purpose	Requests the relay key procedure to start by carrying the relay-specific request parameters needed by the network to derive or return the required security information.
Main specification	3GPP TS 24.501, 8.2.34
Release added	Release 17
Procedures where used	Relay key procedure, Relay security handling, ProSe relay context
Related timers	Procedure dependent
Related cause values	Relay key request parameter semantics

What is Relay Key Request in simple terms?

Relay Key Request is the NAS message used to request relay-related keying material so the relay security procedure can continue in a 5G relay or ProSe relay context.

Requests the relay key procedure to start by carrying the relay-specific request parameters needed by the network to derive or return the required security information.

Why this message matters

Relay Key Request is the UE asking the network for relay-related keying information in a specialized 5G relay security procedure.

Where this message appears in the call flow

Relay Key Procedure

Call flow position: Opening request message used to trigger relay key handling.

Typical state: The UE has already reached relay-aware NAS context and now needs the network to provide relay key response material.

Preconditions:

Relay-capable context exists.
The UE has parameters for the relay key request.

Next likely message: Relay Key Accept or Relay Key Reject

ProSe Relay Security Handling

Call flow position: UE-originated request step before relay key response processing.

Typical state: The procedure is focused on relay-specific security rather than generic registration.

Preconditions:

Relay transaction context exists.

Next likely message: Relay Key Accept

Call flow position

Previous message(s): Relay authentication context establishment, Protected NAS relay-capable context

Next message(s): Relay Key Accept, Relay Key Reject

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 requester and the network NAS entity

Security context: This message belongs to the relay-key handling branch, so it should be interpreted together with ProSe relay context, relay transaction identity, and the later Relay Key Accept or Relay Key Reject.

Message Structure Overview

Relay Key Request is a specialized NAS relay-security message rather than a mainstream registration or service message.
In trace analysis, engineers usually inspect the relay transaction identity first and then the request parameters that drive the network response.

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 Key Request follows NAS 24.501 IE structure and is not an ASN.1 message.

Decoded Message Dump

Relay Key Request
  Extended Protocol Discriminator: 5G Mobility Management
  Security Header Type: Integrity protected and ciphered
  Message Type: Relay Key Request
  ProSe Relay Transaction Identity: 7
  Relay Key Request Parameters: 0x01020304...

How to read this dump

The message is best read as a relay-security request wrapper whose value comes from the relay transaction identity and request parameters.
The next useful check is whether the network answers with Relay Key Accept or Relay Key Reject.

Important Information Elements

IE	Required	Description
`ProSe relay transaction identity`	Yes	Identifies the relay key transaction so the request and later response can be correlated.
`Relay key request parameters`	Yes	Carries the relay-specific request data the network needs to generate the appropriate response.

Detailed field explanation

`ProSe relay transaction identity`

Identifies the relay key transaction so the request and later response can be correlated.

Presence: Required

`Relay key request parameters`

Carries the relay-specific request data the network needs to generate the appropriate response.

Presence: Required

What to check in logs and traces

Confirm the message appears in a relay-capable NAS context rather than a normal registration-only path.
Inspect the ProSe relay transaction identity.
Check the relay key request parameters and correlate them with the expected relay scenario.
Look for the immediate Relay Key Accept or Relay Key Reject response.

Common Issues and Troubleshooting

Relay Key Request is sent but no usable relay response follows.

Likely cause: The relay request parameters may be invalid, unsupported, or inconsistent with the relay context.

What to inspect: Check the relay transaction identity, request parameters, and whether the network returns Relay Key Reject.

Next step: Correlate the message with the surrounding relay authentication and relay-session context.

Relay key handling fails even though NAS connectivity is otherwise normal.

Likely cause: The issue may be specific to the relay security branch rather than the general NAS path.

What to inspect: Focus on relay-specific IEs and the later relay-key response, not on ordinary registration messages.

Next step: Compare with a known-good relay procedure trace and verify relay feature support on both UE and network sides.

Detailed explanation

5G NAS - Relay Key Request Explained

Relay Key Request is a specialized NAS message used in the relay security branch of the 5G system. It is not a mainstream registration message. Instead, it appears when the UE needs the network to process relay-related key request information and continue the relay key procedure.

For beginners, the simple meaning is: the UE is asking the network for relay-related security key handling.
For engineers, the key point is that this message belongs to a relay-specific procedure, so it should be read with relay transaction context rather than with ordinary registration logic.

What is Relay Key Request in simple terms?

The UE needs relay-related key information. It sends Relay Key Request so the network can process the request and respond with either relay key acceptance or rejection.

Why Relay Key Request matters

This message matters because it marks the start of a specialized relay security branch. If engineers treat it like an ordinary NAS message without looking at the relay context, the trace quickly stops making sense.

The most useful practical checks are:

whether the relay transaction identity is valid
whether the request parameters fit the intended relay scenario
whether the next network branch is accept or reject

Where Relay Key Request appears in the call flow

UE                              Network
|--- Relay Key Request --------->|
|<-- Relay Key Accept / Reject --|

It is best interpreted as part of a relay key procedure rather than as part of ordinary registration or service 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 Key Request means operationally

Operationally, Relay Key Request tells engineers that the trace has entered a relay-specific security exchange.

That means the first questions are not the usual registration questions. Instead, ask:

what relay transaction is this message tied to
what request parameters were sent
did the network return Relay Key Accept or Relay Key Reject

Important Information Elements

IE	Why it matters
`ProSe Relay Transaction Identity`	Ties the request to a specific relay-key transaction.
`Relay Key Request Parameters`	Carries the relay-specific security request details the network needs to process.

Example message dump

Relay Key Request
  Extended Protocol Discriminator: 5G Mobility Management
  Security Header Type: Integrity protected and ciphered
  Message Type: Relay Key Request
  ProSe Relay Transaction Identity: 7
  Relay Key Request Parameters: 0x01020304...

How to read this dump

Start with the relay transaction identity.
Then inspect the relay key request parameters.
After that, move directly to the next network response, because the accept-or-reject branch usually defines the practical outcome.

What to check in logs

verify that the message appears in a relay-specific NAS context
inspect the relay transaction identity
check the relay key request parameters carefully
correlate the request with Relay Key Accept or Relay Key Reject

FAQ

What does Relay Key Request do in 5G?

It starts the relay key exchange by asking the network to process relay-specific key request parameters and return the corresponding relay key response.

Is Relay Key Request a normal registration message?

No. It belongs to a specialized relay security procedure rather than the standard registration path.

What usually comes after Relay Key Request?

The usual next branch is Relay Key Accept or Relay Key Reject.

Summary

Relay Key Request is the NAS message used to request relay-related keying material so the relay security procedure can continue in a 5G relay or ProSe relay context.

Advanced Engineer Notes

This is a niche Release 18-era message, so most engineering value comes from correct relay-context correlation rather than from the outer NAS wrapper alone.
If this message appears in a trace, analysts should switch mindset from mainstream 5GMM flow analysis to relay-specific security procedure analysis.

Related message pages

Related Procedures

Relay Key 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.