Specifications

Overview of Dial Interfaces, Controllers, and Lines
ISDN Service
DC-12
Cisco IOS Dial Technologies Configuration Guide
ISDN BRI
ISDN BRI operates over most of the copper twisted-pair telephone wiring in place. ISDN BRI delivers
a total bandwidth of a 144 kbps via three separate channels. Two of the B channels operate at 64 kbps
and are used to carry voice, video, or data traffic. The third channel, the D channel, is a 16-kbps signaling
channel used to tell the Public Switched Telephone Network (PSTN) how to handle each of the B
channels. ISDN BRI is often referred to as “2 B + D.”
Enter the interface bri command to bring up and configure a single BRI interface, which is the overseer
of the 2 B + D channels. The D channel is not user configurable.
The following example configures an ISDN BRI interface on a Cisco 1600 series router. The isdn spid
command defines the service profile identifier (SPID) number for both B channels. The SPID number is
assigned by the ISDN service provider. Not all ISDN lines have SPIDs.
Router# configure terminal
Router(config)# interface bri 0
Router(config-if)# isdn spid1 55598760101
Router(config-if)# isdn spid2 55598770101
Router(config-if)# isdn switch-type basic-ni
Router(config-if)# ip unnumbered ethernet 0
Router(config-if)# dialer map ip 172.168.37.40 name hq 5552053
Router(config-if)# dialer load-threshold 70
Router(config-if)# dialer-group 1
Router(config-if)# encapsulation ppp
Router(config-if)# ppp authentication chap pap callin
Router(config-if)# ppp multilink
Router(config-if)# no shutdown
ISDN PRI
ISDN PRI is designed to carry large numbers of incoming ISDN calls at point of presences (POPs) and
other large central site locations. All the reliability and performance of ISDN BRI applies to ISDN PRI,
but ISDN PRI has 23 B channels running at 64 kbps each and a shared 64 kbps D channel that carries
signaling traffic. ISDN PRI is often referred to as “23 B + D” (North America and Japan) or “30 B + D”
(rest of the world).
The D channel notifies the central office switch to send the incoming call to particular timeslots on the
Cisco access server or router. Each one of the B channels carries data or voice. The D channel carries
signaling for the B channels. The D channel identifies if the call is a circuit-switched digital call or an
analog modem call. Analog modem calls are decoded and then sent to the onboard modems.
Circuit-switched digital calls are directly relayed to the ISDN processor in the router. Enter the interface
serial command to bring up and configure the D channel, which is user configurable.
Figure 10 shows the logical contents of an ISDN PRI interface used in a T1 network configuration. The
logical contents include 23 B channels, 1 D channel, 24 time slots, and 24 virtual serial interfaces (total
number of B + D channels).