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NASLTEMME to UE3GPP TS 24.301
LTE Service Reject
Service Reject is the EPS NAS message the network sends when the service request procedure is not accepted.
Message Fact Sheet
Protocol
nas
Network
lte
Spec
3GPP TS 24.301
Spec Section
5.6.1, 8.2.24
Direction
MME to UE
Message Type
EMM signaling
Full message name
LTE Service Reject
Protocol
NAS
Technology
LTE
Direction
MME to UE
Interface
N1 over LTE access / S1-MME control path
Signaling bearer / channel
NAS signaling / Commonly carried in downlink NAS transport when the network decides not to accept the service request procedure
Typical trigger
Sent when the network cannot accept the requested service restoration because of subscription, congestion, CS fallback restrictions, forbidden-area handling, or related service-control reasons.
Main purpose
Rejects the service restoration attempt, returns the main EMM cause for the failed resume path, and may provide timers or forbidden-area information that change how the UE should retry or stop.
Main specification
3GPP TS 24.301, 5.6.1, 8.2.24
Release added
Release 8
Procedures where used
LTE Service Request Procedure, Idle to Connected Service Restoration, Paging Response, Mobile-Originated Data Resumption
Service Reject is the EPS NAS message the network sends when the service request procedure is not accepted.
Rejects the service restoration attempt, returns the main EMM cause for the failed resume path, and may provide timers or forbidden-area information that change how the UE should retry or stop.
Why this message matters
Service Reject is the network telling the UE that the requested LTE/EPS service restoration was not accepted and what kind of retry or wait behavior should follow.
Where this message appears in the call flow
Mobile-originated service restoration rejection
In mobile-originated service restoration, Service Reject ends the restore attempt and returns the cause and timer branch the UE must follow next.
Call flow position: Reject message sent after the UE attempted to restore active service from idle using stored EPS context.
Typical state: UE remains without resumed active service even though it still had a service-restoration trigger.
Preconditions:
The UE sent Service Request.
The network decided not to grant the requested restore path.
Next likely message: Retry later, backoff waiting, or alternative NAS handling depending on the returned cause
Paging response service restoration rejection
After paging, Service Reject shows that the restore path did not continue into active service and that the UE must follow the returned reject handling.
Call flow position: Reject message sent after the UE responded to paging but the network does not allow the requested restore path to continue.
Typical state: UE answered the paging-driven restore attempt but does not move into active service.
Preconditions:
Paging triggered the restore path.
The service request continuation was rejected by the MME.
Next likely message: Timer-driven waiting or no normal service continuation
Service recovery after idle return rejected
When the UE still had stored context after idle return, Service Reject explains why the direct restore path still failed and whether retry timing applies.
Call flow position: Reject message used when the UE still had stored context but the resume attempt after idle return is not accepted.
Typical state: UE does not rebuild through attach yet, but the direct restore-service path has failed.
Preconditions:
Valid or apparently valid stored EPS context existed.
The network refused the current service restore attempt.
Next likely message: Retry timing, fallback handling, or later broader NAS recovery
Next message(s): Retry after timer expiry, No active service continuation, Wider NAS recovery or mobility handling
Message direction and transport
Sender and receiver: MME to UE
Interface: N1 over LTE access / S1-MME control path
Domain: Core-side EPS mobility management signaling that ends the current service restoration attempt and determines the next UE behavior
Signaling bearer: NAS signaling
Logical channel: Commonly carried in downlink NAS transport when the network decides not to accept the service request procedure
Transport / encapsulation: EPS NAS message sent by the MME and delivered to the UE through the eNodeB when service restoration is rejected
Security context: Normally sent as a protected NAS message in the service request procedure, although some cause-handling depends on the protection state and specific access conditions.
Message Structure Overview
Service Reject is an EPS mobility-management message rather than an ASN.1 LTE RRC structure.
The practical reading path starts with EMM cause, then moves into T3442, T3346, or T3448 when present, and only then into any optional forbidden-TAI or related handling.
In real traces, this is the message that tells you why the restore-service path stopped and what the UE should do next.
ASN.1 Message Syntax for LTE Service Reject
Service Reject
EMM cause
T3442 value OPTIONAL
T3346 value OPTIONAL
T3448 value OPTIONAL
Forbidden TAI(s) for the list of roaming OPTIONAL
Forbidden TAI(s) for regional provision of service OPTIONAL
Lower bound timer value OPTIONAL
How to read this message syntax
Service Reject is a NAS layer-3 message, not an ASN.1 LTE RRC message. Read this NAS syntax from the EMM cause first, then inspect any optional reject timers and forbidden-TAI information because those fields explain the UE's next restore-service behavior.
LTE Service Reject - Example Dump
Service Reject
Protocol discriminator: EPS mobility management
Security header type: Integrity protected and ciphered
Message type: Service Reject
EMM cause: CS service temporarily not available
T3442 value: 30 seconds
T3346 value: 2 minutes
How to read this dump
Start with EMM cause because it defines the rejected service branch.
T3442, T3346, and T3448 are the next fields to inspect because they directly change retry timing and congestion handling.
If the restore path fails after paging or mobile-originated activity, this message is often the clearest explanation point for what the UE is expected to do next.
May provide control-plane user-data congestion timing when that feature is in use.
Forbidden TAI(s) for roaming
Optional
May provide forbidden tracking areas for roaming in relevant access conditions.
Forbidden TAI(s) for regional provision of service
Optional
May provide forbidden tracking areas for regional service conditions in relevant access conditions.
Lower bound timer value
Optional
May guide minimum storage time for the affected PLMN condition when the related cause is used.
Detailed field explanation
EMM cause
Gives the main reason why the network rejected the service request procedure.
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.
T3442 value
May be included when the EMM cause is #39 and CS service is temporarily unavailable.
Presence: Optional
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.
T3346 value
May provide NAS-level congestion backoff information.
Presence: Optional
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.
T3448 value
May provide control-plane user-data congestion timing when that feature is in use.
Presence: Optional
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.
Forbidden TAI(s) for roaming
May provide forbidden tracking areas for roaming in relevant access conditions.
Presence: Optional
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.
Forbidden TAI(s) for regional provision of service
May provide forbidden tracking areas for regional service conditions in relevant access conditions.
Presence: Optional
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.
Lower bound timer value
May guide minimum storage time for the affected PLMN condition when the related cause is used.
Presence: Optional
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.
What to check in logs and traces
Confirm which Service Request the reject belongs to.
Inspect the EMM cause first.
Check whether T3442, T3346, or T3448 was returned.
Inspect any forbidden-TAI information when regional or roaming behavior looks unusual.
Correlate the reject with the UE's next retry, wait state, or lack of service continuation.
Common Issues and Troubleshooting
The UE restores access from idle but active service still does not start.
Likely cause: Service Reject is ending the restore path and the returned cause or timers define why the network refused to continue.
What to inspect: Check EMM cause first, then inspect T3442, T3346, T3448, and any forbidden-TAI information.
Next step: Treat the returned reject branch as the main explanation before debugging bearers or user plane.
Paging response is seen, but the later service never resumes.
Likely cause: The UE may have reached the service request path, but the network responded with Service Reject and timer-driven handling.
What to inspect: Check Paging, Service Request, Service Reject, and the returned timers together.
Next step: Read the paging-driven restore attempt as a complete sequence rather than stopping at the radio response.
Service restoration behaves differently across cells or after restart.
Likely cause: The network may return different EMM causes, different temporary restrictions, or different forbidden-TAI information.
What to inspect: Compare the Service Reject IE set across working and failing cases.
Next step: Use Service Reject as the primary explanation point for the changed service-restoration branch.
LTE / 5G / Variant Comparison
Compared with Service Accept
Service Accept grants service restoration using existing EPS context. Service Reject ends the restore attempt and returns the failure branch the UE must follow.
Compared with Service Request
Service Request starts the restore-service path. Service Reject is the network response when that path is not accepted.
Compared with Attach Reject
Service Reject blocks service restoration while EPS registration context still exists. Attach Reject blocks creation or rebuilding of EPS registration context itself.
FAQ
What is Service Reject in LTE?
It is the EPS NAS message the network sends when the service request procedure is rejected.
What should I inspect first in Service Reject?
Start with the EMM cause, then inspect any returned T3442, T3346, T3448, or forbidden-TAI information.
Why is Service Reject important in troubleshooting?
Because it explains not only that service restoration failed, but also which reject branch and retry behavior the UE is expected to follow.
What usually comes after Service Reject?
That depends on the returned cause and timers: the UE may wait, retry later, or remain without normal active 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.
