Dear, ulva
TCH call Blocking , it present how many subscriber asks for TCH channel and network reply with no avaliable resource.
so it present how many subscriber request TCH channel to reject this request
TCH call drop
after subscriber get TCH and start converstion
during it the call is dropped for some reasons not related to the subscribers .
also for SDCCH call drop rate the same
but SDCCH not for call,it is signaling channel
also SDCCH blocking rate(%)
the same for TCH blocking
i hope it is clear
may be you can expalin what you need with more calarifaction