LTE Roaming
The purpose of this tutorial is to show you how to perform Roaming Tests with LTE network.
This tutorial shows how to test Cell Reselection on Amari Callbox and a commercial UE. Cell Reselection is a mechanism where UE can change the cell in Idle mode. The idle mode cell change happens in several different situations as listed below. When we say 'Cell Reselection', it usually mean the first two cases, but people say in a little different way depending on context.
- UE changes cell to another cell which has higher cell power with the same PLMN as the current cell.
- UE changes cell to another cell which has higher priorities. This priorities may be configured in SIB or RRC Release message.
- UE lost signal from the current cell and change to another cell with selectable cell. Strictly speaking this is more like a cell selection, but it can be considered as a type of reselection.
- UE first attached to a visiting PLMN and changes to another cell with Home PLMN and vice versa. Strictly speaking this is called Roaming.
- UE attached to a cell and Network (eNB) explcitely direct UE to change to another cell via RRCConnectionRelease message. This is called Cell Redirection.
Table of Contents
- LTE Roaming
Test Setup
In this tutorial, you may use two types of as shown below. All the components will launch automatically by lte service and all the components will be automatically added to 'screen' window as well.
Configuration
For this tutorial, you can use two types of the setup as below.
: eNB with two PLMN, two MME and IMSs are running indepentaly as illustrated above, so configuration is pretty complicated. I used the exact same configuration as in the tutorial : Multiple MME.
Perform the test
First with UE, power on UE and disable Mobile Data for both HPLMN cell and VPLMN Cell. (
Go to [1 ENB] screen and confirm that UE attaches to Cell 1 (HPLMN).
Now turn off HPLMN Cell. VPLMN cell (ENB1) remain active.
Make it sure that UE attaches to VPLMN cell. This takes a while (a few min) for UE to camp on to VPLMN Cell. You would see Roaming Icon displayed on the phone.
Confirm that UE attaches to Cell 2 (VPLMN).
Now power on HPLMN Cell gain. At this moment, both HPLMN and VPLMN cell are active and UE is registered to VPLMN Cell.
Wait until UE camp on to HPLMN Cell. This would take several minutes for UE to search for High Priority PLMN (HPLMN) cell.
Now you would see the HPLMN icons on UE when it completes the attach to the HPLMN Cell.
Log Analysis
In this log, I would not look into any specific message. I will just take a look at a few blocks of messages to check to which cell the UE is connected.
First, Confirm that UE is connected to the first cell (HPLMN Cell). You can identify the cell by checking the number in 'Cell' column.
Once the UE is roamed to VPLMN cell, you should see that the UE is now connected to Cell 2.
After roaming back to HPLMN cell, you should see that UE is attached to Cell 1.
