User`s guide

XSR User’s Guide 189
Chapter 9 Understanding ISDN
Configuring Integrated Services Digital Network (ISDN)
Understanding ISDN
Physically, an ISDN line is provisioned via unshielded twisted pair cable
which would, in the absence of ISDN service, be used for regular analog
telephone service or a T1/E1 connection.
Typically, numerous ISDN devices connect onto this single line through a
device known as an NT1 provided by the user in North America and by the
carrier most everywhere else. PRI service is terminated in the XSR’s T1/E1
NIM the same way as E1 or T1 service. BRI service is connected to the XSR’s
BRI-S/T NIM via a interface adapter known as NT1. The NT1 is provided by
the service provider. Only in North America do users have to provide their
own NT1. The BRI U NIM can be connected directly to incoming BRI lines in
North America as they include a built-in NT1.
Logically, ISDN consists of two types of communications channels: bearer
service B-channels, which carry data and services at 64 Kbps; and a single D-
channel (delta), which usually carries signaling and administrative
information which is used to set up and tear down calls. The transmission
speed of the D-channel depends on the type of ISDN service you've
subscribed to.
Available ISDN services include two categories: Basic Rate Interface (BRI)
service, which provides access to two B-channels and a 16 Kbps D-channel;
and Primary Rate Interface (PRI) service, which provides access to 23 B-
channels in North America and Japan and 30 B-channels in Europe and most
of Asia, and a 64 Kbps D-channel in both.
Basic Rate Interface
The XSR’s BRI NIM provides two BRI ports. Each port has two 64 Kbps B-
channels and one 16 Kbps D-channel. BRI is configured on the XSR by
interface bri sub-commands.
Primary Rate Interface
ISDN PRI is provisioned over T1 service in North America and Japan and
includes one 64 Kbps D-channel and 23 B-channels, and over E1 service
includes 30 B-channels in most other parts of the world.