According to the Erlang principle, we have:
7TCH/TRX
0,5Er/TCH
It means that 1TRX = 3,5 Erlangs;
Those principles permit us to dimension the BSS equipement.
For exemple,
1PCM = 1Ater = 30CIC
1CIC = 0,88Er —> 1Ater = 22Er
If we want to add 22Er trafic, we must add 1Ater in the BSC, 30CIC at the MSC side, and 1 PCM must be available for carring.