| Protocol | nas | Network | 5g |
|---|---|---|---|
| Spec | 3GPP TS 24.501 | Spec Section | 8.2.16 |
| Direction | AMF to UE | Message Type | 5GMM signaling |
| Full message name | 5G NAS - Service Reject |
|---|---|
| Protocol | NAS |
| Technology | 5G |
| Direction | AMF to UE |
| Interface | N1 |
| Signaling bearer / channel | NAS signaling / Dedicated NAS message, commonly via DL Information Transfer |
| Typical trigger | Sent when the network cannot accept the requested service continuation. |
| Main purpose | Stops the current service-request path and tells the UE that active service cannot be restored under the current conditions. |
| Main specification | 3GPP TS 24.501, 8.2.16 |
| Release added | Release 15 |
| Procedures where used | Service Request |
| Related timers | T3346 when applicable |
| Related cause values | 5GMM cause |
Service Reject is the NAS message the network sends when a service request is refused even though the UE already has registration context.
Stops the current service-request path and tells the UE that active service cannot be restored under the current conditions.
Service Reject means the network refused to restore active service even though the UE already had registration context.
Call flow position: Negative AMF response after Service Request.
Typical state: UE is registered but service resumption was not accepted.
Preconditions:
Next likely message: Retry or alternative recovery depending on cause
Previous message(s): Service Request
Next message(s): Backoff, retry, or alternative signaling behavior
Security context: Usually protected because it follows a protected Service Request path.
This message is not typically analyzed as ASN.1 on the wire. It is usually read as a NAS or protocol field structure instead.
Service Reject is a NAS message defined in 24.501.
Service Reject
Extended Protocol Discriminator: 5G Mobility Management
Security Header Type: Integrity protected and ciphered
Message Type: Service Reject
5GMM Cause: UE not reachable for requested service
| IE | Required | Description |
|---|---|---|
5GMM cause | Yes | Explains why the requested service continuation was refused. |
5GMM causeExplains why the requested service continuation was refused.
Presence: Required
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
Likely cause: The AMF refused service continuation after evaluating the Service Request.
What to inspect: Check the Service Reject cause and the service type requested earlier.
Next step: Troubleshoot by cause instead of treating the issue as only radio-side.
It means the UE was registered, but the network did not accept the requested service continuation.
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.