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LTE E-RAB Release Procedure Call Flow

call-flowLTE | S1AP | E-RAB | eNB

LTE E-RAB Release Procedure removes one or more active E-RABs from the access side. It is used when the MME wants the eNB to release bearer-specific radio resources because service ended, a bearer was deactivated, or a later control path is cleaning up the UE context.

The main S1AP pair is E-RAB Release Command and E-RAB Release Response.

Introduction

The E-RAB release path is the radio-access side of bearer cleanup. It does not necessarily mean the whole UE context is gone, but it does mean that specific E-RAB resources are being removed from the eNB-side view.

The main nodes are the MME, eNB, and UE.

What Is LTE E-RAB Release Procedure in Simple Terms?

What starts the procedure: The network decides active E-RAB resources should be removed.
What the UE and network want to achieve: Cleanly release selected radio bearer resources.
What success looks like: The eNB receives E-RAB Release Command and returns E-RAB Release Response.
What failure means: Access-side bearer cleanup stays partial or stale radio resources remain.

Why this procedure matters

This procedure shows why an otherwise healthy bearer or service branch disappears from the radio side and whether that release was complete.

Quick Fact Sheet

Procedure name	LTE E-RAB Release Procedure
Domain	Access-side bearer cleanup
Main trigger	Release of one or more active E-RABs
Start state	eNB has active E-RAB resources for the UE
End state	Target E-RAB resources are removed
Main nodes	MME, eNB, UE
Main protocols	S1AP
Main success outcome	eNB releases the requested E-RAB items cleanly
Main failure outcome	Radio-side cleanup is incomplete
Most important messages	E-RAB Release Command, E-RAB Release Response
Main specs	TS 36.413, TS 23.401

LTE E-RAB Release Procedure call flow across MME, eNB, and UE — Click the diagram to open the full-size in a new tab.

Preconditions

One or more E-RABs are still active at the eNB.
The MME has a reason to release those E-RABs.
The UE context on S1-MME is still available for targeted cleanup.

Nodes and Interfaces

Nodes involved

Node	Role in this procedure
MME	Starts the E-RAB release toward the eNB.
eNB	Releases the requested access-side bearer resources.
UE	Stops using the released radio bearer resources after cleanup.

Interfaces used

Interface	Path	Role
S1-MME	MME <-> eNB	Carries E-RAB Release Command and Response.
LTE Uu	UE <-> eNB	Reflects the later absence of the released radio resources.

End-to-End Call Flow

UE               eNB               MME
|                 |<-- E-RAB Release Cmd -|
|                 |-- release bearer ctx -|
|                 |-- E-RAB Release Resp ->|
|   released E-RAB no longer usable        |

Major Phases

Phase	What happens
1. Release decision	The MME decides which E-RAB resources should be removed.
2. Access-side cleanup	The eNB releases the requested E-RAB items.
3. Result reporting	The eNB reports completion or partial failure back to the MME.

Step-by-Step Breakdown

Step 1: E-RAB Release Command

Sender -> receiver: MME -> eNB

Message(s): E-RAB Release Command

Purpose: Ask the eNB to release specific E-RAB resources.

State or context change: The eNB begins bearer-specific cleanup.

Note: Inspect which E-RAB IDs are included and why they are being removed.

Step 2: E-RAB Release Response

Sender -> receiver: eNB -> MME

Message(s): E-RAB Release Response

Purpose: Confirm which E-RABs were successfully released.

State or context change: The MME now knows whether the access-side cleanup finished correctly.

Note: Partial release handling matters in multi-bearer sessions.

Important Messages in This Flow

Message	Protocol	Direction	Purpose in this procedure	What to inspect briefly
E-RAB Release Command	S1AP	MME -> eNB	Starts radio bearer release at the access side.	E-RAB IDs, release reason, and UE context identifiers.
E-RAB Release Response	S1AP	eNB -> MME	Reports the result of the requested release.	Released list, failed items, and partial cleanup details.

Important Parameters to Inspect

Parameter	What it is	Where it appears	Why it matters	Common issues
E-RAB ID	The access bearer being released.	Release Command and Response	Shows exactly which bearer resources are being removed.	Wrong item released or failed item mapping.
Cause	The reason attached to the release branch.	Release Command	Helps separate normal cleanup from failure-led removal.	Release reason interpreted incorrectly.
S1AP UE IDs	The UE context identifiers on S1-MME.	Command and Response	Keep the release tied to the correct UE context.	Stale UE mapping.

Successful Completion

Success is confirmed when the eNB returns E-RAB Release Response and the target E-RAB resources disappear from the access-side UE context.

Common Failures and Troubleshooting

Symptom	Likely cause	Where to inspect	Relevant message(s)	Relevant interface(s)	Likely next step
Some E-RABs release, but others remain	The eNB completed only part of the cleanup.	Per-item result details in the response.	E-RAB Release Command, E-RAB Release Response	S1-MME	Check the failed item list and the earlier bearer history.
Bearer looks released in EPC, but not at the access side	Access-side cleanup did not complete or did not target the correct UE context.	UE IDs and E-RAB IDs in the command.	Release Command and Response	S1-MME, LTE Uu	Align the S1AP release with the bearer deactivation branch.

What to Check in Logs and Traces

Match E-RAB IDs in the command and response before checking later traffic behavior.
Use the cause and earlier bearer history to decide whether the release was normal or failure-led.
Correlate access-side cleanup with any NAS bearer release that happened at the same time.

Related sub-procedures

Related message reference pages

LTE Initial Context Setup Procedure — common earlier bearer setup path

Related troubleshooting pages

Notes

E-RAB release is access-side cleanup. It may happen because of normal service teardown or because another bearer-control branch has already started removing the session.

FAQ

What is LTE E-RAB Release Procedure?

It is the S1AP procedure used to remove active E-RAB resources from the eNB side.

What is the main success message?

E-RAB Release Response is the clearest confirmation that the requested access-side cleanup finished.