| in-band signaling
ISDN normally uses a separate wire
called the D channel to set up calls and handle their signals. In some
locations, this third wire isn't available, and bandwidth must be
"borrowed" from the other two data-carrying B channels. For Basic Rate
Interface (BRI) service, this means that each B channels is limited to 56
kbps throughput (instead of 64 kbps with out-of-band signaling). |