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CHAPTER
A-1
Cisco 800 Series Routers Hardware Installation Guide
78-5373-04
A
ISDN and IDSL Concepts
This appendix provides further explanation of ISDN and IDSL concepts.
The Cisco 800 series routers provide one basic rate interface (BRI). The ISDN BRI service provided by
your telephone service provider offers two bearer channels (B channels) and one data channel (D
channel). The B channel operates at 64 kbps and carries user data. The D channel operates at 16 kbps
and carries control and signaling information although it can support user data transmission under
certain circumstances.
Cisco 801 and Cisco 803 routers have an ISDN S/T port. Cisco 802 and Cisco 804 routers have an ISDN
U port, and Cisco 802 IDSL and Cisco 804 IDSL routers have an IDSL port.
Outside North America, telephone service providers typically provide an S/T interface. The S/T
interfaces are four-wire (two pairs of wires) interfaces from the phone switch that supports full-duplex
data transfer over two pairs of wires.
In North America, telephone service providers typically provide a U interface. The U interface is a
two-wire (single pair) interface from the phone switch that supports full-duplex data transfer over a
single pair of wires.
Cisco 803 and Cisco 804 routers support data and voice applications. The data applications on these
routers are implemented through the ISDN port on these routers. The voice applications on these routers
are implemented with ISDN BRI and through the telephone ports.