Glossary definition of Mobile Switching Centre

Also known as: MSC

The MSC (Mobile Switching Centre) is a part of a GSM network that is the equivalent of an exchange in a fixed network, plus everything extra needed to handle mobile stations. The MSC sits upstream of the BSS, and its major jobs are authentication, location management, handovers, registration and the routing of calls to roaming mobile stations.

MSCs communicate with registers in the GSM network over its interfaces using SS7 and SS7-based protocols. The SS7-based protocols that the MSC uses to communicate are: MAP, TCAP, ISUP, INAP, and TUP. If the MSC also has a gateway for communicating with other networks, it is called Gateway MSC (GMSC).

To handle roaming mobile stations, each mobile switching centre has its own VLR which is usually physically integrated into the MSC hardware. Each VLR has exactly one MSC.

The MSC manages all handoff and switching between cells, providing commands to each relevant BS in order to drop the call from the old BS and set up the new one. To make sure calls stay active as much as possible, the MSC usually assigns voice channels to handoff calls over new calls.

Mobile Switching Centres also orchestrate the process of creating new voice calls. An MS will initiate the call by using a reverse control channel to make a request. The MSC has to then grant the request, after which a pair of voice channels are assigned for the call.