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LTE ETWS Notification Procedure Call Flow

call-flow LTE | ETWS | Warning | Paging | Broadcast

LTE ETWS Notification Procedure is the LTE warning-delivery path used when the network needs to expose Earthquake and Tsunami Warning System information to UEs through the broadcast and warning-related LTE context.

This procedure depends on the broadcast chain, warning-related SIB handling, and in some cases the paging-side path that alerts idle UEs to warning-related changes.

Introduction

The LTE ETWS Notification Procedure is a public-warning path rather than a normal UE-specific service procedure. It is centered on how the warning reaches the UE through LTE broadcast behavior.

Use this page when the main question is whether the warning-related LTE context was present, refreshed, and visible to the UE at the time it should have been.

What Is LTE ETWS Notification Procedure in Simple Terms?

What starts the procedure: The network activates ETWS-related warning broadcasting for the cell or area.
What the UE and network want to achieve: Expose the warning-related broadcast context to the UE quickly and reliably.
What success looks like: The UE receives the warning-related LTE context and behaves as expected for the warning scenario.
What failure means: The warning-related broadcast path is incomplete, stale, or missed by the UE.

Why this procedure matters

Warning delivery analysis is mostly about whether the right broadcast and reachability context was present at the right time. If the UE never saw the warning-related LTE context, later paging or idle behavior may look normal while the actual warning path still failed.

Quick Fact Sheet

Procedure name	LTE ETWS Notification Procedure
Domain	LTE public warning broadcast
Main trigger	ETWS warning activation by the network
Start state	UE is camped or monitoring LTE broadcast behavior in the warning area
End state	UE has the warning-related LTE context needed for ETWS handling
Main nodes	UE, eNB
Main protocols	RRC broadcast information, paging-side reachability where relevant
Main success outcome	The warning-related broadcast context is visible to the UE
Main failure outcome	The warning path is missed, stale, or only partly visible
Most important messages	SIB1, warning-related SIB family, Paging where relevant
Main specs	TS 36.331, TS 36.300

LTE ETWS Notification Procedure Call Flow — Click the diagram to open the full-size in a new tab.

Preconditions

The UE has valid LTE broadcast context for the serving cell.
The cell or area is configured to expose ETWS-related warning context.
The UE is in a state where warning-related LTE context should be observable.

Nodes and Interfaces

Nodes involved

Node	Role in this procedure
UE	Reads warning-related LTE broadcast context and reacts to it.
eNB	Schedules the warning-related LTE broadcast content and any related reachability behavior.
Broadcast warning context	Provides the warning-related LTE information made visible to UEs in the affected area.

Interfaces used

Interface	Path	Role
LTE Uu	UE <-> eNB	Carries the warning-related LTE context.
BCCH / DL-SCH	eNB -> UE	Carry the warning-related system-information content.
Paging-side path	eNB -> UE	May alert idle UEs to system-information change or warning-related continuation.

End-to-End Call Flow

UE                         eNB / warning context
|--idle monitoring----------->|
|<--Paging (if used)----------|
|<--SIB1 / SI change----------|
|<--ETWS-related broadcast----|

Major Phases

Phase	What happens
1. Warning activation	The network activates the ETWS-related warning path.
2. Reachability or change indication	Idle UEs may be alerted through paging-side or SI-change behavior.
3. Warning-related broadcast read	The UE reads the warning-related LTE context.
4. UE-side warning visibility	The UE now has the warning-related information exposed through LTE broadcast handling.

Step-by-Step Breakdown

Start from the current broadcast context

Sender -> receiver: UE

Message(s): SIB1 and existing system-information view

Purpose: Anchor the warning analysis in the current LTE broadcast state.

State or context change: The UE has the basic cell view needed before warning-specific handling can be checked.

Note: Do not start ETWS analysis without proving the normal broadcast path first.

Check whether the UE was alerted to a change

Sender -> receiver: eNB -> UE

Message(s): Paging or SI-change-driven continuation

Purpose: Explain how an idle UE became aware that warning-related context needed attention.

State or context change: The UE is positioned to refresh or observe the warning-related LTE context.

Note: Not every trace shows the same alerting pattern, so keep the broadcast and paging context together.

Read the warning-related LTE context

Sender -> receiver: eNB -> UE

Message(s): Warning-related SIB family within LTE system information

Purpose: Expose the ETWS-related warning information to the UE.

State or context change: The UE now has the warning-related LTE broadcast view.

Note: The public-warning SIB family is best read through the LTE system-information reference on this site.

Correlate the warning visibility with UE behavior

Sender -> receiver: UE

Message(s): Warning handling continuation

Purpose: Check whether the warning-related broadcast information was actually usable at the UE.

State or context change: The warning path is now visible as either successful or incomplete.

Note: The key question is whether the UE saw the warning context at the right time, not only whether the cell was broadcasting in theory.

Important Messages

Message	Protocol	Direction	Purpose in this procedure	What to inspect briefly
System Information Block Type 1	RRC	eNB -> UE	Provides the scheduling and change-detection context behind later warning handling.	Check whether the UE had the right baseline broadcast context before the warning path.
Paging	RRC	eNB -> UE	May support idle-side warning-related continuation or SI-change awareness.	Check whether an idle UE had a clear path back to the warning-related broadcast refresh.
LTE System Information Reference	RRC	eNB -> UE	Maps the public-warning SIB family used for ETWS-related handling.	Check the warning-related SIB family through the LTE system-information reference.

Important Parameters to Inspect

Parameter	What it is	Where it appears	Why it matters	Common issues
Warning-area context	The area or cell scope where the warning was meant to be visible.	Broadcast and idle context	Needed to confirm the UE was in the intended warning area.	The UE was not on the intended warning-side cell or area.
SI-change visibility	Whether the UE had a clear reason to refresh the warning-related broadcast set.	SIB1 and paging-side context	Explains how the UE knew to re-read the warning-related context.	The warning content changed, but the UE never refreshed its view.
Warning-related SIB presence	Whether the public-warning SIB family was actually present and readable.	LTE system-information view	Shows whether the warning content was available to the UE at all.	The warning was expected, but the related broadcast block was absent or stale.
Idle reachability state	Whether the UE was in a state where warning-related continuation was plausible.	RRC_IDLE and paging context	Useful when the warning path depends on idle-side awareness.	The paging-side state is ignored during warning analysis.
Broadcast timing	When the warning-related context became visible compared with when the UE was monitoring.	Across SI refresh and warning activation	Useful when the warning path is time-sensitive.	The UE monitored earlier or later than the actual warning broadcast window.

Successful Completion

Success means the UE had a valid path to the warning-related LTE broadcast context and the ETWS-related information became visible in time.

Common Failures and Troubleshooting

Symptom	Likely cause	Where to inspect	Relevant message(s)	Relevant interface(s)	Likely next step
The cell was in the warning area, but the UE never showed warning-related behavior	The warning-related broadcast context may have been stale, absent, or never refreshed at the UE.	SIB1, paging context, and the warning-related SIB family.	SIB1, Paging, warning-related SIBs	LTE Uu	Check how the UE would have become aware of the warning-related broadcast change.
Paging is present, but the warning path still looks incomplete	The alerting path existed, but the broadcast warning content may still not have been readable.	Paging plus the later system-information refresh path.	Paging and warning-related system information	LTE Uu	Do not assume paging alone proves the warning content reached the UE.

What to Check in Logs and Traces

Prove the normal broadcast baseline before checking warning-specific behavior.
Read paging and SI-change context together when the UE was idle.
Use the LTE system-information reference for the warning-related SIB family.

Related sub-procedures

Related message reference pages

Related troubleshooting pages

Notes

This page treats ETWS as a broadcast warning path. On this site, the public-warning blocks are best read through the LTE system-information reference rather than standalone message pages.

FAQ

What is the LTE ETWS Notification Procedure?

It is the LTE broadcast warning path used to expose ETWS-related information to UEs in the affected area.

Which LTE references matter most for ETWS analysis?

Start with the LTE system-information path, then check the paging-side context if idle UEs had to become aware of a broadcast change.