1/ there is certainly a good reason for it… let’s see:
a speech frame contains speech for 20ms.
and with GSM codecs and protection, 20ms of speech are coded in 456 bits.
so you need a net bit rate of 456 bits / 20ms..
I’ll stop here because i don’t see how you can link that to 8TS/TRX… 🙂
2/ there is no transcoder in the BSC. the transcoder is a dedicated equipment, outside the BSC. And one BSC is connected to one transcoder via Ater interfaces.