1.It can be located on either side.Usually it is near to MSC to reduce A-interface E1 cost.
2.1 A-ter E1=30 circuits.
1 TRX=8 circuits
Now i think you can calculate yourself.
Also take A-ter utilisation as 70%(max) while dimnsioning.
2.1 Ater E1=4 A-inteface E1.
This calculation is valid for TDM mode only.If you are using Abis over IP or HDLC,the calculated A-ter E1 will be quite less
if you are in Ericsson,let me know,as this calculation is bit different there.
Hi Ater being the dynamic path-i.e circuts get allocated only on need basis.So better ,if its to be calculated on the basis of carried traffic(Erlang) rather than number of circuits because if 90% TCH are configured as TCHD(dual rate-HR/FR),then total Ater requirement comes very high.In india still Abis is on TDM based PCMs,ofcourse Gb path genertally configured as Gb over IP.
U can send ur email id so that i can send an excel sheet with calculation(formulaes also there)