PSTN – Public Switched Telephone Network

GMSC – Gateway MSC

MSC – Mobile Switching Center

BSC – Base Station Controller

BTS – Base Transceiver Station

MSCs are the telephone exchanges of GSM networks. They route the calls based on the destination numbers current location. The BSCs and BTS are responsible to taking the call from the MSC to the handset. Those two components together handle the complications in the radio communication part.

The Gateway MSC is used to connect networks that follow different protocols. PSTN and GSM and connected via a GMSC which will take care of the signaling conversions. Old PSTN networks were analog networks, but now a days the internal network functions of a PSTN are digitally managed and uses the ss7 protocol. Only the end user connectivity is still maintained as analog.