N7 : there is a “N7” TS on the A interface (BSC – MSC) that carries all the “N7” signalling 🙂
this signalling is used to carry call setup information (Authentication, Ciphering, Calls Numbers, Handover Messages, etc)
1 N7 Timeslot can take care of 120 calls.
The call itself (the TCH if you prefer) is carried by another A nterface timeslot, which is called the “CIC”)
Cheers
pix