ISDN
The Integrated Services Digital Network is a telecommunications standard for
transmitting voice, video, and data over digital lines running at 64 Kbps.
ISDNÆs basic service is Basic Rate Interface (BRI), which is made up of two 64 Kbps
B channels and one 16 Kbps D channel (2B+D). If both channels are combined
into one, called bonding, the total data rate becomes 128 Kbps and is four and a
half times the bandwidth of a V.34 modem (28.8 Kbps).
ISDNÆs high-speed service is Primary Rate Interface (PRI). It provides 23 B
channels and one 64 Kbps D channel (23B+D), which is equivalent to the 24 channels of
a T1 line. When several channels are bonded together, high data rates can be
achieved. For example, it is common to bond six channels for quality
videoconferencing at 384 Kbps. In Europe, PRI includes 30 B channels and one D channel,
equivalent to an E1 line.