Hi Neeraj,
Basically 1 TRX has 8 Timeslots, out of which the first & Second TS are allocated for BCCH & SDCCH.
So the total available traffic channels in a TRX is 6.
Hence for 6 channels @ 2% GoS, we find in Erlang-B table the offered erlang as 2.28.
This stands true for various configuration of BTS.