Dear Kamal,
TCH Blocking: is the phase where all the TCHs are occupied, and no more MS seizures requesting a TS taking place. (i.e. 14 TS all occupied and no more subscribers asking for a TCH-TS, just before congestion)
TCH Congestions: is the phase where all the TCHs are occupied and there are MS seizures requesting TSs taking place( i.e. 14 TS all all occupied and there is at leats one subscriber asking for a TCH-TS)
Hope it is clear.
Regards,