LTE IMS SMS

This tutorial shows how to test SMS over IMS with a commercial UE on Amari Callbox. We have been using SMS in every radio technology (i.e, 3G, 4G, 5G) and user interface on commercial mobile phone would look same whatever radio technology is used, but the detailed protocol behind the SMS differs with the radio access technology being used.

• 3G : SMS go through NAS messages carried by CS(Circuit Switch) channel
• LTE : Two different ways are used
• SG SMS : SMS go through NAS message  // check out this tutorial for SG SMS
• SM over IMS : SMS go through IMS  // this is the topic for this tutorial.
• 5G : SMS goes through IMS

One common thing regardless of the method listed above is that the way SMS message is being encoded and protocols at the level of session menagement (i.e, CP-DATA, CP-ACK etc).  Putting it other way, same format of SMS and session layer protocol is encapsulated in different way (i.e, NAS message or IMS) depending on different radio technology.

NOTE :  In most of the cases, the user interface on commericial phone would look same regardless of what kind of technology is used. Usually the UI on mobile phone select what type of technology to use depending on protocols status at the specific moment. So when you want to test a specific type of SMS, you need to know how to configure your UE(DUT) to apply the specific SMS technology you want to test.

If you are using the USIM card from Amarisoft, you don't need to change any settings in the default configuration (You just need to understand about the settings on default configuration) The setting change for this test would be mainly with UE side configuration setting.

Table of Contents

• LTE IMS SMS
• Test Setup
• Key Configuration Parameters
• Configuration
• Perform the test
• MO SMS
• MT SMS
• Log Analysis
• MO SMS over IMS
• MT SMS over IMS

NOTE : For some additional / summarized tips on SG SMS testing, refer to this wiki.

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.

• impi
• impu
• domain

Configuration

I used the enb.default.cfg (LTE default configuration) as it is without changing any contents in it.

I also used the default configuration for mme as shown below. Since this test is to send / receive SMS via IMS, ims.cfg and ue_db-ims.cfg is important configurations. Unless your DUT(UE) requires any specific configuration, the default configuration (i.e, ims.default.cfg and ue_db-ims.cfg) would work.

In mme-ims.cfg file, you would notice that ue_db-ims.cfg is used as ue db.

In this tutorial, I am using Anritsu Test USIM. Remember tel number since these will be used for SMS. If you are using any other test USIM/ISIM, change the parameters accordingly. For SMS test, remember 'tel' numbers specified here since the numbers will be used to send SMS in this test.

I did following configuration on UE side. First make sure that UE has 'ims' APN configured. In most of UE, the 'internet' and 'ims' APN would be configured by default. But for some UE, you may need to manually configure 'ims' APN.  In addition, you may need to enable 'VoLTE' option because the UE may not initiate IMS registration if VoLTE is not turned on.

Perform the test

You can do both MO(Mobile Originated) SMS and MT(Mobile Terminated) SMS with Amarisoft Callbox.

MO SMS

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

Power On UE and make it sure that UE get registerred.

Make it sure that UE is assigned with IMS pdn. If UE successfully completed IMS registration, you would see 2 (or more) BEARER established and see three IP_ADDR. Usually the first IP is for internet APN and the 2nd/3rd IPs are for IMS APN.

Following is indicating that UE is registered to IMS server.(NOTE : To test SMS over IMS, this is precodition for the test. If you don't see any users shown here, you cannot do SMS over IMS. So if you don't see any user here, troubleshoot IMS registration process first.)

Make it sure that sms volte option is supported and remember 'tel' number because it is the number you need to use to send SMS to.

Send SMS from UE and you will get the result as follows. (NOTE : In terms of SMS operation on UE side, you would not see any difference between SMS over SG and SMS over IMS. But in the background, different procedure is used on depending on UE status and UE internal implemenation)

You should send a SMS message to 'tel' number that you see in the result of '(ims) users' command. If the message is successfully send to SMS center of Callbox, you will get the echo back from the server (NOTE : In Amarisoft callbox, IMS server functions as SMS Center)

MT SMS

Reaching to this point, the procedure is same as in MO SMS.(NOTE : To test SMS over IMS, this is precodition for the test. If you don't see any users shown here, you cannot do SMS over IMS. So if you don't see any user here, troubleshoot IMS registration process first.)

For MT SMS, send SMS from (ims} screen as shown below.  The command to send SMS from callbox is 'sms <tel> <message>' for example sms 600 "Test for MT SMS over IMS"

You should receive the SMS message on your phone as shown below.

Log Analysis

MO SMS over IMS

Enable at least NAS, SIP, IMS in WebGUI log. Filter it out with NAS, SIP, IMS for convenience

First make it sure that UE completed the IMS registration.

The SIP message  'MESSAGE' is the one that carries SMS message over IMS. You can check the contents of sms (decoded SMS) in the panel on the right. You see an IMS SMS message 'SMS <src> <dest> recieved' message. The print 'recieved' indicates it is MO SMS. The SIP MESSAGE that you see in this screenshot is the SIP message used to carry the SMS.

Right after the callox (SMS Center) received an SMS, it echos back the same message to UE.

MT SMS over IMS

IMS Registration part is same as in MO SMS over IMS. The only difference would be the part shown below. You see an IMS SMS message 'SMS <src> <dest> sent' message. The print 'sent' indicates that it is MT message.