<P> Each B - channel carries data , voice , and other services . The D - channel carries control and signaling information . Larger connections are possible using PRI pairing . A dual T1 - PRI could have 24 + 23 = 47 B - channels and 1 D - channel ( often called `` 47B + D '' ) , but more commonly has 46 B - channels and 2 D - channels thus providing a backup signaling channel . The concept applies to E1s as well and both can include more than 2 PRIs . When configuring multiple T1 's as ISDN - PRI 's , it 's possible to use NFAS ( non-facility associated signalling ) to enable one or two D - channels to support additional B - channels on separate T1 circuits . </P>
isdn uses b & d channels . what is d channel use for
control and signaling information