to mr madhu,
Yr question is not BTS part, it is transmission part. Here i give y a basic idea about this.
There are various capacity configuration of transmission like..
e1,e2,e4 etc. are 1e1=2m, 2e1=4m etc. are are not synchronization, i.e PDH. also for pdh equipment are different.
on the otherhand in SDH (synchronization digital hierarkey) are stm1=155m,stm4=622m,stm16,stm64=10g etc. also sdh equipment are different.