cially in new installations. Wiring is particularly important when connecting
ISDN videoconferencing equipment to internal PBX equipment. Some
administrators use Category 5 wiring for internal ISDN connections,
although Category 3 is acceptable. This chapter focuses on the Basic Rate
Interface, which operates over standard copper pairs.
differs from the available primary rate interface (PRI), which uses a T1 as the
conduit. The primary rate of telecommunications connections is usually
measured in DS-1 increments. A DS-1, or T1, is equivalent to 24T1 voice
channels. The basic rate for a voice connection is referred to as a DS-0, or a
single 64Kbit channel of the T1. In ISDN, this refers to the single B-channel
capacity of the circuit. The formal description of BRI is specified in I.430,
whereas the I.431 specification addresses PRI ISDN.
out-of-band management. In addition, the D-channel function of BRI is used
for replacement of legacy X.25 networks.
64Kbps. The third channel provides 16Kbps of bandwidth for commands
and signaling, and is referred to as the D channel. The remaining bandwidth
of 48Kbps is overhead.