Polycom ViewStation - Manual (Page 239)

Glossary
© Polycom, Inc. 223 ViewStation User Guide
Broadband ISDN (2 Mbps - 600 Mbps). ISDN
usually consists of 2 B channels of 64 Kbps,
and one D channel of 16 Kbps on one RBI
(basic rate interface). The D channel is used
for out-of-band signaling that does not
interfere with the flow of information going
through the B channels.