This tutorial shows how to do VoLTE Loopback test with a commercial UE on Amari Callbox. VoLTE loopback means UE initiate VoLTE call and Callbox accept the call and loopback the SIP/RTP back to UE. There is no independent receiving UE. If you are using USIM card from Amarisoft, you don't need to change anything in default LTE configuration. You just need to do some settings on UE side.

There are two main technology to implement Voice in LTE as below.

NOTE : Since Amarisoft Callbox VoLTE is based on Loopback mechanism, most of the connected property (e.g, type of Voice Codec) is determined by UE capability, not determined by Callbox feature.


Table of Contents


NOTE : For a generic technical tips about VoLTE test, refer to this wiki.



Test Setup

Test setup for this tutorial is as shown below.  

TestSetup Callbox UE 1sdr 01


Key Configuration Parameters

Followings are important configuration parameters for this tutorial. You may click on the items for the descriptions from Amarisoft documents.



NOTE : Amarisoft callbox support VoLTE by default setting. So unless you have any specific configurations of your own on device side, VoLTE should work with default settings.

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

LTE SG SMS Config 01

I also used the default configuration for mme (mme-ims.cfg)  as shown below.

LTE SG SMS Config 03

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

LTE SG SMS Config 04

In this tutorial, I am using Anritsu Test USIM.

LTE SG SMS Config 05

Following setting is for VoLTE loopback configured in ims.default.cfg. If you make a call to this number from the phone, the Callbox will do VoLTE loopback.

LTE VoLTE Loopback Config 05


I did following configuration on UE side.  Make it sure that ims PDN is added (NOTE : There can be some cases wehre  UE would have ims APN but would not display it in settings. Check out the UE setting details of your DUT) and make it sure that VoLTE is enabled (NOTE : There might be some case where UE would not register to IMS when Roaming is turned off. So it would be safe to try with Roaming ON first)

LTE VoLTE Loopback Config 06


Perform the test

In this test, I will show you with both MO and MT VoLTE call.


Test 1 : VoLTE Loopback

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

LTE VoLTE Loopback Run 01

Power On UE and make it sure that UE get registerred. (NOTE : If UE is in idle mode, you would not see anything listed here. Then just proceed to next step)

LTE VoLTE Loopback Run 02

Make it sure that UE IS assigned with IMS pdn.

LTE VoLTE Loopback Run 03

Following is indicating that UE is registered to IMS server.

LTE VoLTE Loopback Run 04


Make a call to 666 ('666' is VoLTE loopback number specified in the configuration file) and check if the call gets established and hear loopback sound

LTE VoLTE Loopback Run 05

Check the trace log in (ims) and you would see the call status as shown below.

LTE VoLTE Loopback Run 06


Test 2 : MT Call from WebGui

You can make an MT Call from the WebGUI as follows : (Go into [IMS] pannel and find a UE that is regisered to IMS server. Then hit on a registerred UE and it will make a call to UE(DUT).

LTE VoLTE Loopback Run Test2 01

If everything (VoLTE signaling flow) goes well, you will get the alert (Ring) on your mobile phone. Hit [ANSWER] and see if the call go through.

LTE VoLTE Loopback Run Test2 02

If you want to disconnect the call, hit on [-] icon.

LTE VoLTE Loopback Run Test2 03


Log Analysis

Sample Log

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

First check out the IMS/SIP registration sequence.  (NOTE : If you want to look into the protocol details of the registration process, check out this note)

LTE VoLTE Loopback Log 01

When you make a call, you would see the INVITE process for the call setup. (NOTE : If you are interested in the detailed protocol in this step, check out this note and this note )

LTE VoLTE Loopback Log 02