Hii yash
E1 contain 32 channel each channel have 64kb/s, 2 channel for synchronization and signalling so we have 30channel, if you use 4+4+4 config. that is mean you have 90calls in BTS, each call coding 16kb/s if you used full rat and 8kb/s for half rate or less,if you used full rate, in one channel from 30 channel we can send 4calls because each call have 16kb/s 16+16+16+16kb/s=64kb/s. for 90calls we will use 24 channel from E1 and there 6channel are empty.
Regard
Ahmed