Manual Migration and Rollback of UEs in the MSC Pool Networking

If the MSC is faulty or needs to be upgraded, you can migrate UEs from the faulty MSC to another MSC.

The migration is divided into the following phases:

• Phase 1: UE-triggered migration. When the UE initiates a combined attach, periodic routing area update (RAU) procedure or tracking area update (TAU) procedure, the MME selects another MSC for the UE.
• Phase 2: MME-triggered migration. The MME sends an IMSI detach request to the UEs that have not been migrated in phase 1, for example, UEs in connected state. During the TAU procedure, the MME selects another MSC for the UEs and implement the UE migration.

After having initiated the UE migration, whenever needed, you can issue a command to terminate the migration. Upon receiving the termination command, the OMS starts the migration rollback. When a UE initiates combined attach, periodic RAU procedure or TAU procedure, the MME forcibly updates the SGs interface and allocates the UE back to the original MSC. Most UEs can be migrated back to the original MSC after one RAU period.

Figure 3 shows the procedures for manual migration and rollback of UEs in the MSC pool networking.