LTE EMM Status | NAS Message

Message Fact Sheet

Protocol	nas	Network	lte
Spec	3GPP TS 24.301	Spec Section	Release 18 message definition for EMM Status
Direction	UE to MME	Message Type	EMM signaling

Full message name	LTE EMM Status
Protocol	NAS
Technology	LTE
Direction	UE to MME
Interface	N1 over LTE access / S1-MME control path
Signaling bearer / channel	NAS signaling / Sent during established EMM signaling when an EMM protocol error is detected.
Typical trigger	Triggered when an EMM message is semantically wrong, in the wrong state, or contains invalid mandatory information.
Main purpose	Carries an EMM cause value so the peer can understand why the received EMM message could not be processed correctly.
Main specification	3GPP TS 24.301, Release 18 message definition for EMM Status
Release added	Release 8
Procedures where used	EMM protocol error handling
Related cause values	EMM cause

What is LTE EMM Status in simple terms?

EMM Status is the LTE NAS message used to report an EMM protocol error, invalid state, or message-format problem back to the peer.

Carries an EMM cause value so the peer can understand why the received EMM message could not be processed correctly.

Why this message matters

EMM Status is the LTE NAS message used to report an EMM protocol error.

Where this message appears in the call flow

Protocol-state mismatch reporting

LTE flow showing EMM Status after a protocol-state mismatch — If the received EMM message does not fit the current state, the peer can answer with EMM Status.

Call flow position: Error-report message sent when the received EMM message does not fit the current protocol state.

Typical state: The branch is active, but the peer sent an EMM message that cannot be handled in the current state.

Preconditions:

An EMM message was received.
The receiving side detected a protocol-state mismatch.

Next likely message: Procedure abort or later corrected signaling

Invalid information reporting

LTE flow showing EMM Status after invalid EMM information — EMM Status can also report that the previous EMM message was malformed or missing mandatory information.

Call flow position: Error-report message sent when mandatory information is missing or invalid in an EMM message.

Typical state: The receiving side rejects the current EMM message but does not decode it as a success path.

Preconditions:

An EMM message contained invalid or missing information.

Next likely message: Procedure abort or recovery handling

Call flow position

Previous message(s): Authentication Request, Security Mode Command, EMM Information

Next message(s): Procedure abort, Protocol recovery handling

Message direction and transport

Sender and receiver: UE to MME

Interface: N1 over LTE access / S1-MME control path

Domain: Core-side EPS mobility-management error reporting.

Signaling bearer: NAS signaling

Logical channel: Sent during established EMM signaling when an EMM protocol error is detected.

Transport / encapsulation: EPS NAS EMM message sent by the UE or network in response to an incompatible or invalid EMM message.

Security context: Usually seen in protected NAS continuation because it reports an error on an already active EMM branch.

Message Structure Overview

EMM Status is the generic EMM-layer error-reporting message.
In traces, the main value is the EMM cause and the message that triggered it.

ASN.1 Message Syntax for LTE EMM Status

EMM Status
  EMM cause

How to read this message syntax

Read EMM Status from the returned EMM cause first and then correlate it with the message that triggered the protocol error.

LTE EMM Status - Example Dump

EMM Status
  Protocol discriminator: EPS mobility management
  Security header type: Integrity protected and ciphered
  Message type: EMM Status
  EMM cause: Message type not compatible with protocol state

How to read this dump

Start with the EMM cause.
Then identify the earlier EMM message that triggered the status response.

Important Information Elements

IE	Required	Description
`EMM cause`	Yes	Explains why the received EMM message could not be processed.

Detailed field explanation

`EMM cause`

Explains why the received EMM message could not be processed.

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.

What to check in logs and traces

Identify the message immediately before EMM Status.
Inspect the EMM cause first.
Decide whether the issue is state mismatch, malformed information, or unsupported message handling.

Common Issues and Troubleshooting

An EMM procedure stops without a normal reject or success outcome.

Likely cause: The branch may have ended with EMM Status because one side treated the previous EMM message as invalid.

What to inspect: Check the earlier EMM message and the returned EMM cause.

Next step: Treat the branch as protocol error handling rather than normal reject logic.

FAQ

What is EMM Status in LTE?

It is the LTE NAS message used to report an EMM protocol error or invalid message handling condition.

Related message pages

Related Procedures

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.