<P> PRI is the standard for providing telecommunication services to enterprises and offices . It is based on T - carrier ( T1 ) transmission in the US , Canada , and Japan , while the E-carrier ( E1 ) is common in Europe and Australia . The T1 line consists of 23 bearer ( B ) channels and one data ( D ) channel for control purposes , for a total bandwidth of 24x64 - kbit / s or 1.544 Mbit / s . The E1 carrier provides 30 B - and two D - channels for a bandwidth of 2.048 Mbit / s . The first timeslot on the E1 is used for synchronization purposes and is not considered to be a B - or D - channel . The D - channel typically uses timeslot 16 on an E1 , while it is timeslot 24 for a T1 . Fewer active bearer channels , sometimes called user channels , may be used in fractional T1 or E1 services . </P>
isdn uses b & d channels . what is d channel use for
data