LTE ETWS
This tutorial shows how to test LTE ETWS on Amari Callbox with a commercial phone. ETWS stands for Earthquake and Tsunami Warning System. It is a type of PWS (Public Warning System). Basic RAN Process of LTE ETWS is as follows :
- Transmit SIB10 with ETWS Message Info (Message ID, Serial Number, Warning Type)
- Transmit SIB11 with ETWS Message Contents
- Transmit Paging to inform UE to decode the ETWS
In real deployment, this process is controlled by ETWS server in core network side. It is the ETWS server and Core Network which are triggering the whole ETWS process and RAN to transmit the message.
Table of Contents
Introduction
The Earthquake and Tsunami Warning System (ETWS) is a critical component of the Public Warning System (PWS) architecture standardized in LTE networks, designed to rapidly disseminate emergency alerts such as earthquake and tsunami warnings to mobile devices within affected regions. Leveraging the robust broadcast capabilities of LTE radio access networks (RAN), ETWS enables the delivery of time-sensitive, high-priority notifications to all compatible user equipment (UEs), ensuring maximal reach and minimal delay. The system operates through a coordinated process: the core network's ETWS server initiates the warning cascade, orchestrating message creation, scheduling, and transmission commands to the RAN. The eNodeB (LTE base station) then conveys the ETWS notifications via System Information Blocks (SIB10 and SIB11) over broadcast channels, and triggers paging procedures to prompt UEs to immediately decode the incoming alert. Unlike legacy 2G/3G broadcast solutions, which utilized dedicated channels such as CTCH over FACH-SCCPCH, LTE's PWS repurposes existing broadcast channels (typically BCCH mapped onto PDSCH) for efficient, streamlined operation. This architecture not only enhances network resource utilization but also ensures compatibility with commercial LTE devices. In this context, the Amari Callbox system from Amarisoft offers a testbed environment for validating ETWS broadcast behavior and UE response using commercial off-the-shelf phones. Understanding the interplay between core network signaling, RAN message broadcasting, and UE decoding mechanisms is essential for telecom engineers, network testers, and emergency communication solution developers seeking to ensure compliance, reliability, and effectiveness of ETWS in real-world deployments.
-
Technology Context and Background
- ETWS is part of the broader LTE PWS framework, enabling mass delivery of emergency alerts using standardized procedures and interfaces.
- The system leverages core network components (e.g., ETWS server, MME) to trigger and manage alerts, while the RAN (eNodeB) broadcasts messages to all UEs in the coverage area.
- SIB10 provides ETWS message metadata (such as message ID, serial number, and warning type), while SIB11 carries the actual warning content.
- The paging procedure ensures that UEs promptly decode the ETWS message upon reception.
- Unlike 2G/3G CBS implementations, LTE PWS uses existing broadcast channels, improving spectrum efficiency and reducing implementation complexity.
- Amarisoft’s Amari Callbox provides a controlled environment for simulating and testing LTE ETWS procedures with commercial devices.
-
Relevance and Importance of the Tutorial
- Demonstrates practical ETWS testing on Amari Callbox, equipping professionals with hands-on experience in LTE emergency broadcast systems.
- Facilitates understanding of critical LTE PWS procedures, contributing to the reliability and compliance of public warning deployments.
- Provides insights into differences between LTE PWS and legacy CBS mechanisms, highlighting architectural evolution.
- Supports validation of commercial device compatibility and behavior in response to ETWS alerts.
-
Learning Outcomes
- Gain a comprehensive understanding of LTE ETWS architecture and broadcast mechanisms.
- Learn to configure and operate Amari Callbox for ETWS message transmission and UE testing.
- Acquire the ability to analyze and interpret UE behavior in response to ETWS paging and broadcast messages.
- Develop awareness of standards compliance and best practices for public warning systems in LTE networks.
-
Prerequisite Knowledge and Skills
- Familiarity with LTE network architecture, including the roles of eNodeB, MME, and broadcast channels.
- Basic understanding of System Information Blocks (SIBs) and paging procedures in LTE.
- Experience with test equipment such as Amari Callbox and commercial LTE handsets.
- General knowledge of public warning systems and emergency communication protocols is beneficial.
Summary of the Tutorial
This tutorial provides a step-by-step procedure to test the LTE ETWS (Earthquake and Tsunami Warning System) / CMAS (Commercial Mobile Alert System) broadcast functionality using a callbox and UE setup. The summary below details the test methodologies and procedures as described in the tutorial.
- Test Setup
- Use a SIM card delivered with the system.
- For configuration changes, refer to the Configuration Guide.
- Key Configuration Parameters
- Important parameters for ETWS/CMAS broadcast are set in the pws_msgs section of the MME configuration file.
- Parameters include: local_identifier, message_identifier, serial_number, data_coding_scheme, repetition_period, warning_type, warning_message, warning_message_hex, send_warning_indication, and warning_area_list.
- Configuration
- Use the default LTE eNB configuration file (enb.default.cfg); no special configuration required for ETWS at the eNB.
- Modify mme-ims-etws.cfg to add ETWS-specific pws_msgs configuration. This determines the content of the broadcast message.
- Test Procedure
- Start LTE service and verify cell configuration. Any LTE cell configuration is suitable.
- Power on the UE and allow it to attach to the LTE cell.
- Verify that the UE is successfully attached to the MME.
- Send a CMAS/ETWS message using the pws_write command, specifying the correct local_identifier as configured in pws_msgs.
- Check on the UE for reception of the ETWS/CMAS message:
- Verify both the display of the text message and the sounding of the alarm on the UE. Both are required for a successful test.
- To stop the ETWS message, use the corresponding stop command, again referencing the local_identifier.
- Log Analysis
- Enable logging for BCCH and RRC to capture ETWS broadcast activity.
- Adjust log viewer layers for easier analysis.
- Observe that, upon sending the ETWS message from the core, the eNB broadcasts the ETWS message and sends a Paging message with etws-indication.
- ETWS content is broadcast via SIB10 and SIB11 messages, populated from the pws_msgs configuration.
- To modify the broadcast content for testing, adjust the pws_msgs section in the configuration file.
Throughout the process, the methodology centers on configuring the network to generate ETWS/CMAS alerts, verifying their transmission and reception, and confirming proper behavior on the UE, accompanied by log analysis to validate message flow and content broadcast via SIBs and Paging.
Test Setup
Test setup for this tutorial is as shown below.
- SIM Card used in this tutorial is the one delivered with the system as it is.
- If you want to change the configuration, The tutorial Configuration Guide would help
Key Configuration Parameters
Followings are important configuration parameters for this tutorial. You may click on the items for the descriptions from Amarisoft documents.
- pws_msgs : In this link, you would get the descriptions for all the items listed below. In the document, there are much more parameters (optional parameters) than the list below
- local_identifier
- message_identifier
- serial_number
- data_coding_scheme
- repetition_period
- warning_type
- warning_message
- warning_message_hex
- send_warning_indication
- warning_area_list
Configuration
I used the enb.default.cfg (LTE default configuration) as it is without changing any contents in it. Basically you can use any kind of enb configuration. eNB does not require any specific configuration for ETWS.
I also used mme-ims-etws.cfg which was copied and modified from mme-ims.cfg.
In mme-ims-etws.cfg .I have added the following configuration. pws_msgs is the parameter where you can configure the details of ETWS.
In this example, local_identifier identifies the configured warning entry, while message_identifier and serial_number uniquely identify the warning message. warning_type specifies the ETWS warning category, and data_coding_scheme defines how the message text is encoded. The warning_message field contains the text that will be broadcast to the UE through the ETWS system information.
Perform the test
Start the LTE service and verify the basic cell configuration using the cell phy and cell commands. ETWS is independent of most radio parameters, so any normal LTE cell configuration can be used for this test. In this example, the cell operates on LTE Band 7 with a 5 MHz bandwidth, DL EARFCN 3350, UL EARFCN 21350, PCI 1, and PLMN 00101.
Power on the UE and allow it to attach to the LTE cell.
Use the t command to monitor the live UE status and confirm that the UE is connected and exchanging traffic with the eNB. In this example, UE ID 1 is attached to cell 001 with C-RNTI 003d, and the changing DL/UL MCS, transport block counts, and bitrates confirm active radio communication.
Confirm that the UE is registered with the MME using the ue command. In this example, the UE is registered in EPC mode with SUPI 001010123456789 and M-TMSI 0x52c3793f. The REG field is Y, confirming successful registration, and the UE has two bearers with assigned IPv4 and IPv6 addresses.
Trigger the ETWS warning using the pws_write command. The value 1 selects the pws_msgs entry whose local_identifier is set to 1 in mme-ims-etws.cfg. The MME then initiates the PWS procedure and instructs the eNB to broadcast the configured ETWS warning information and message to the UE.
Confirm that the UE displays the ETWS warning as shown below. The warning should include the configured text message and the earthquake/tsunami warning indication. The UE should also generate the dedicated emergency alert sound. Successful reception of both the visual warning and the alert sound confirms that the ETWS test has completed successfully.
Stop the ETWS warning broadcast using the pws_kill command. The value 1 identifies the active warning whose local_identifier is configured as 1 in the pws_msgs block of mme-ims-etws.cfg. The MME then sends the request to stop broadcasting the corresponding ETWS message.
Log Analysis
Since ETWS information is broadcast through system information messages, begin the log analysis by enabling BCCH capture and setting the RRC layer to debug in the ENB log configuration. BCCH capture allows the broadcast SIB messages to be recorded, while the RRC debug setting provides the decoded RRC contents needed to inspect SIB10 and SIB11.
Set the Layer filter to RRC to display only the relevant RRC messages. This removes unrelated PHY, MAC, S1AP, and other protocol logs, making it easier to locate the Paging, SIB10, and SIB11 messages associated with the ETWS procedure.
When the ETWS procedure is triggered, the MME sends an S1AP Write-Replace Warning Request message to the eNB to start broadcasting the warning. The Message Identifier IE is set to 0x1102 and identifies the warning category, while the Serial Number IE is set to 0x3001 and distinguishes this warning instance from previous or updated warnings. The Warning Type IE is set to 0x0580 and provides the ETWS warning classification used by the UE to determine how the alert should be presented. The Data Coding Scheme IE is set to 0x0F and specifies how the warning text is encoded. The Warning Message Content IE carries the encoded text configured by the warning_message parameter in the pws_msgs block. The Repetition Period IE is set to 10 and defines the interval between repeated broadcasts, while Number of Broadcasts Requested is set to 65535, requesting continuous repetition until the warning is explicitly stopped with the pws_kill command. After receiving this request, the eNB updates the relevant system information, transmits paging notifications, and begins broadcasting the ETWS information through SIB10 and SIB11.
After receiving the S1AP Write-Replace Warning Request from the core network, the eNB transmits an RRC Paging message on the PCCH with etws-Indication set to true. This indication informs all UEs monitoring the cell that new or updated ETWS information is available in the broadcast system information. The paging message does not carry the warning text itself. Instead, it prompts the UE to immediately read the relevant system information blocks, including SIB10 for the primary ETWS notification and SIB11 for the secondary warning message content.
ETWS information is broadcast through SIB10 and SIB11.
SIB10 carries the ETWS primary notification information. The messageIdentifier 0x1102 identifies the warning category, while serialNumber 0x3001 identifies this specific warning instance and allows the UE to distinguish a new warning from a previously received one. warningType 0x0580 provides the earthquake and tsunami warning classification used by the UE to determine the alert presentation and emergency behaviour. Unlike SIB11, SIB10 does not carry the detailed warning text. It provides the compact, time-critical warning information that allows the UE to raise the primary ETWS alert quickly, while the associated SIB11 messages deliver the detailed text configured by the warning_message parameter.
SIB11 carries the detailed ETWS warning message as a secondary notification. The messageIdentifier 0x1102 and serialNumber 0x3001 associate this SIB11 content with the corresponding SIB10 primary notification. warningMessageSegmentType is set to notLastSegment and warningMessageSegmentNumber is 0, indicating that this is the first segment and that additional warning-message segments follow. warningMessageSegment contains the encoded portion of the configured warning text, while dataCodingScheme 0x0F specifies the character encoding used by the UE to decode it. When the warning content does not fit into a single SIB11 segment, the eNB broadcasts multiple SIB11 instances with increasing warningMessageSegmentNumber values, and the UE reassembles them into the complete ETWS message.
RRC / NAS Signaling
SIB 10
: This is the SIB 10 message sent by eNB to configure ETWS. (
{
message c1: systemInformation: {
criticalExtensions systemInformation-r8: {
sib-TypeAndInfo {
sib10: {
messageIdentifier '1102'H,
serialNumber '3001'H,
warningType '0580'H
}
}
}
}
}
SIB 11
: This is the SIB 11 message sent by eNB to configure ETWS. (
{
message c1: systemInformation: {
criticalExtensions systemInformation-r8: {
sib-TypeAndInfo {
sib11: {
messageIdentifier '1102'H,
serialNumber '3001'H,
warningMessageSegmentType notLastSegment,
warningMessageSegmentNumber 0,
warningMessageSegment '0174747A0E4ACF416150917A9D82E8E5391DD42ECFE7E1731900000000000000'H,
dataCodingScheme '0F'H
}
}
}
}
}
Paging
: This is the Paging message sent by eNB to Notify that ETWS is transmitted. (
{
message c1: paging: {
etws-Indication true
}
}