NR CMAS

 

This tutorial shows how to test NR CMAS on Amari Callbox with a commercial phone. CMAS stands for Commercial Mobile Alert System. It is a type of PWS (Public Warning System). Basic RAN Process of NR CMAS is as follows :

• Transmit SIB8 with CMAS Message

In real deployment, this process is controlled by CMAS server in core network side.  It is the CMAS server and Core Network which are triggering the whole CMAS process and RAN to transmit the message.

NOTE :  In 2G/3G, there was similar feature like PWS. It is called CBS (Cell Broadcasting System). The logic on core network side logic in CBS would be similar to PWS in LTE, but RAN side implementation of CBS is different from PWS in LTE and NR. In LTE/NR, we don't use any specifically dedicated channel for this and just use one of the existing channel (BCCH - PDSCH) whereas we use specially dedicated channel (CTCH - FACH-SCCPCH) for CBS.

NOTE :  Amarisoft does not support any of 2G/3G (i.e, GSM,CDMA,WCDMA,HSPA) and 2G/3G related function.

 

 

Table of Contents

• NR CMAS
• Test Setup
• Key Configuration Parameters
• Configuration
• Perform the test
• Log Analysis
• RRC / NAS Signaling
• SIB 8

 

 

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 gnb-sa.cfg (NR SA default configuration) as it is without changing any contents in it.

I also used mme-ims-cmas.cfg which was copied and modified from mme-ims.cfg.

In mme-ims-cmas.cfg I have added the following configuration. Just add pws_msgs configuration and specify the details like local_identifier, message_identifier, serial_number, data_coding_scheme, warning_message etc.

 

Perform the test

Start LTE service and check basic cell configuration. Any cell configuration is OK as long as it is NR cell.

Power on UE and let UE attach to the cell

Confirm that UE is attached to mmel

Send CMAS using pws_write command as shown below. (NOTE : The number '2' corresponds to the configuration parameter local_identifier of pws_msgs:[ ] in mme.cfg)

 

Check if you get CMAS message as shown below. You should hear alarm sound from the UE as well. Both text message and Alarm sound is requirement for the test.

 

You can stop cmas message using the following command. (NOTE : The number '2' corresponds to the configuration parameter local_identifier of pws_msgs:[ ] in mme.cfg)

 

Log Analysis

Sample Log

Since CMAS message is broadcast by SIB message triggered by Core Network, the first step for CMAS log analysis is to capture the log with BCCH, RRC and NGAP enabled as shown below.

Set the layer as shown below for the convinience of the log analysis.

When you send the CMAS message message (triggered by mme command 'pws_write'), Core Network send NGAP message for CMAS  as shown below.|

CMAS message is broadcast via sib8. In this SIB you can check out the details of CMAS contents : messageIdentifier, serialNumber, warningMessageSegmentType, warningMessageSegmentNumber, warningMessageSegment, dataCodingScheme.

When you stop the CMAS message message (triggered by mme command 'pws_kill'), Core Network send NGAP message for CMAS  as shown below.|

 

 

RRC / NAS Signaling

 

SIB 8

: This is the SIB 8 message sent by gNB  to configure CMAS. (NOTE : You would see some IEs that has a specific assigned vale here, but consider it as just an example value. Those values should vary depending on test requirement)

{

  message c1: systemInformation: {

    criticalExtensions systemInformation: {

      sib-TypeAndInfo {

        sib8: {

          messageIdentifier '1112'H,

          serialNumber '3001'H,

          warningMessageSegmentType notLastSegment,

          warningMessageSegmentNumber 0,

          warningMessageSegment '0174747A0E4ACF4161D0B0199C82E8E5391DD42ECFE7E1731900000000000000'H,

          dataCodingScheme '0F'H

        }

      }

    }

  }

}