E1 SIGNALLINGBasically our local mobile architecture depends on three things which are BTS, BSC and MSC

First our system catches signal from BTS (base transciever station) then VIA MIcrowave dishes the call go towards BSC then via another medium may be microwave. MSC is the responsible for originating and terminating process and users identity, services , value added services and EIR (Equipment identity register) also in MSC which is responsile for good or black list mobile if all proceses done the call will be originated for local or for other network.

Basically there are 8 time slots on each TRX(transmit recieve) each slot data rate of 16kbps  means 128kbps of 1 channel. Basically first for popup process(the process in which users restarts or open cell first time) and most probabily 1 slot for rest for voice calls. Each site can not support not more than 120 users voice calls at same time.

Other about Protocol we use SS7(switching signalling) as a protocol of  GSM network.  There are 32 time slots in E1 . Each E1 time slot of 64kbps. so 32*64= 2048 = 2Mbps MOst probabily 16 time slot for SS7 signalling.E1 is just a medium.

For further  information do  question more.