LTE VoLTE

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.

• CSFB (CS Fallback) : This is the technology that switch the call to CS network (i.e, 2G or 3G network). This technology is used when UE does not support VoLTE (Voice over IMS) or LTE Network with VoLTE is not available. Amarisoft does not support this method since we don't support any 2G / 3G capability.
• VoLTE (Voice over LTE) : This is the technoligy based on IMS and SIP/RTP. This is the native (built-in) technology for Voice in LTE.

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

• LTE VoLTE
• Test Setup
• Key Configuration Parameters
• Configuration
• UE DB Configuration
• IMS Configuration
• Perform the test
• Test 1 : VoLTE Loopback
• Test 2 : MT Call from WebGui
• Log Analysis

NOTE : For a generic technical tips about VoLTE test, 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.

• echo
• tel
• impu
• precondition
• 100rel
• ipsec_aalg_list
• ipsec_ealg_list

Configuration

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.

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

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

UE DB Configuration

In this tutorial, I am using Anritsu Test USIM.

NOTE : impi and impu (except tell) is set here by default is based on the assumption that UE derive those numbers from imsi. If it is not the case for your UE(DUT), set the proper impi, impu based on your UE implementation, otherwise you would get errors during IMS registraton or various other SIP messaging which carries IMPI or IMPU.

IMS Configuration

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.

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)

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.

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)

Make it sure that UE IS assigned with IMS pdn.

Following is indicating that UE is registered to IMS server.

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

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

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).

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.

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

Log Analysis

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)

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 )