LTE Activate Default EPS Bearer Context Reject

Message Fact Sheet

Protocol	nas	Network	lte
Spec	3GPP TS 24.301	Spec Section	6.4.1.3, 8.3.5
Direction	UE to MME	Message Type	ESM signaling

Full message name	LTE Activate Default EPS Bearer Context Reject
Protocol	NAS
Technology	LTE
Direction	UE to MME
Interface	N1 over LTE access / S1-MME control path
Signaling bearer / channel	NAS signaling / Sent as the failure branch after Activate Default EPS Bearer Context Request.
Typical trigger	Triggered when the UE cannot apply the returned default bearer configuration.
Main purpose	Returns the ESM cause that explains why the UE rejected the proposed default bearer definition.
Main specification	3GPP TS 24.301, 6.4.1.3, 8.3.5
Release added	Release 8
Procedures where used	Default EPS Bearer Context Activation Procedure
Related timers	T3485
Related cause values	ESM cause

What is LTE Activate Default EPS Bearer Context Reject in simple terms?

Activate Default EPS Bearer Context Reject is the LTE NAS message the UE sends when it cannot accept the default bearer the network tried to activate.

Returns the ESM cause that explains why the UE rejected the proposed default bearer definition.

Why this message matters

Activate Default EPS Bearer Context Reject means the UE did not accept the default bearer the network offered.

Where this message appears in the call flow

Initial attach default bearer reject

LTE flow showing Activate Default EPS Bearer Context Reject during attach — If the UE cannot accept the default bearer returned during attach, it can reject the bearer activation branch.

Call flow position: UE reject message sent when the default bearer inside the attach-related branch cannot be accepted.

Typical state: Attach may continue or fail depending on the wider branch, but the proposed bearer itself was not accepted.

Preconditions:

The network sent Activate Default EPS Bearer Context Request.

Next likely message: Attach or PDN failure handling

Standalone default bearer reject

LTE flow showing Activate Default EPS Bearer Context Reject in a standalone PDN branch — The same reject branch can appear after a standalone PDN setup when the proposed default bearer cannot be accepted.

Call flow position: UE reject message sent when a standalone PDN-connectivity branch returned a default bearer the UE cannot accept.

Typical state: The PDN branch is failing at bearer activation time.

Preconditions:

A standalone default-bearer activation branch is active.

Next likely message: PDN failure handling

Additional APN or IMS default bearer reject

LTE flow showing Activate Default EPS Bearer Context Reject for an additional APN such as IMS — An additional PDN branch such as IMS can fail at the same default bearer activation step when the UE cannot accept the returned bearer definition.

Call flow position: UE reject message sent when another PDN connection such as IMS returned a default bearer that the UE cannot apply.

Typical state: The earlier registration may remain intact, but the new PDN branch is failing at default bearer activation time.

Preconditions:

The network returned Activate Default EPS Bearer Context Request for another PDN connection.

Next likely message: Additional APN or IMS failure handling

Call flow position

Previous message(s): Activate Default EPS Bearer Context Request

Next message(s): Bearer setup failure handling

Message direction and transport

Sender and receiver: UE to MME

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

Domain: Core-side EPS session management error handling for default bearer activation.

Signaling bearer: NAS signaling

Logical channel: Sent as the failure branch after Activate Default EPS Bearer Context Request.

Transport / encapsulation: EPS NAS ESM message sent by the UE to reject default bearer activation.

Security context: Protected by the active NAS security context.

Message Structure Overview

Activate Default EPS Bearer Context Reject is the UE-side failure branch of default bearer activation.

ASN.1 Message Syntax for LTE Activate Default EPS Bearer Context Reject

Activate Default EPS Bearer Context Reject
  ESM cause
  Protocol configuration options       OPTIONAL
  Extended protocol configuration options OPTIONAL

How to read this message syntax

Read the ESM cause first because it explains why the UE rejected the proposed default bearer.

LTE Activate Default EPS Bearer Context Reject - Example Dump

Activate Default EPS Bearer Context Reject
  Protocol discriminator: EPS session management
  EPS bearer identity: 5
  Procedure transaction identity: 3
  Message type: Activate Default EPS Bearer Context Reject
  ESM cause: insufficient resources

How to read this dump

The ESM cause is the main field that matters.

Important Information Elements

IE	Required	Description
`ESM cause`	Yes	Explains why the UE rejected the default bearer activation.
`Protocol configuration options`	Optional	May carry additional configuration-side detail related to the reject decision.

Detailed field explanation

`ESM cause`

Explains why the UE rejected the default bearer activation.

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.

`Protocol configuration options`

May carry additional configuration-side detail related to the reject decision.

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

Inspect the earlier default bearer request.
Read the returned ESM cause first.
Check whether the wider PDN or attach branch also failed.

Common Issues and Troubleshooting

The network offered a default bearer, but the UE did not bring it up.

Likely cause: The UE may have rejected the proposed bearer definition.

What to inspect: Check Activate Default EPS Bearer Context Request and the returned ESM cause in the reject.

Next step: Treat the issue as bearer-activation failure rather than only an attach problem.

FAQ

What is Activate Default EPS Bearer Context Reject in LTE?

It is the UE message that rejects the default bearer activation proposed by the network.

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.