redundancy is ISDN (Integrated Services Digital Network). ISDN supports two different types
of interfaces--Basic Rate Interface and Primary Rate Interface:
channel. This is written as 2B+D. The BRI delta channel operates at 16 Kbps, and the
bearer channels each operate at 64 Kbps to the local central office. The total user data rate
on the BRI is 128 Kbps. (As mentioned in Chapter 10, you could use 9.6 Kbps of the delta
channel for X.25 data.)
channel (64 k) in the United States and Japan, usually terminated into an RJ-45. The total
user data rate on the PRI is approximately 1472 K.
a great backup technology with a very fast circuit setup time. Costs vary throughout the world.
Developed in the 1960s, ISDN never had the success that was predicted due to inconsistent
switch configurations used by the telephone companies. Had a simpler standard been put into
place, it might have had much more success. Nevertheless, ISDN is still widely available and
is used by companies (and SOHO users as well) worldwide. Its main drawback is that it is
considered difficult to configure. Another drawback is cost. Throughout the United States, each
regional Bell operating company charged different rates for the same service, adding more
confusion to this digital service. Due to its ability to call multiple sites upon failure, it is a