The ISDN provides for the
integration of voice and data (as well as other formats
such as video and graphics images) over a digital transmission
network. GSM defines its own air interface, or radio interface.
All
other interfaces in GSM,e.g. base transceiver station (BTS) - base
station controller (BSC) and base station controller (BSC) - mobile
services switching center (MSC), are based on 64 Kbit /
s ISDN channels.