Every network has a ratio of successfull cals, handovers etc…
it also has a lot of network hardware… So you can optimise usage of hardware such way that you obtain more capacity from the same hardware or tune that hardware such way that it serve calls better… there are a lot of radio network parameters in every GSM network which can be adjusted… by adjusting parameters you can distribute traffic between gsm900 and gsm 1800 layers, to enable/disable handovers between particular cells etc…
alex
http://www.dx200.biz