Integrated Services Digital Network (ISDN)
Integrated Services Digital Network (ISDN) is an international
communications standard for sending voice, video, and data over
digital telephone lines and standard telephone wires. ISDN has the
ability to simultaneously deliver two connections over a single pair
of telephone lines. The two connections may be
in
any combination of data, voice, video, or fax. The single line uses
an ISDN subscriber service, which is called Basic Rate Interface
(BRI). BRI has two channels, called B channels, at 64 Kbps each,
which carry the data, and one data channel at 16 Kbps for control
information. The two B channels can be combined to form a single 128
Kbps connection.
The
other ISDN transmission rate service, Primary Rate Interface (PRI),
has 23 B channels and one 64 Kbps D channel and uses more wire
pairs. PRI is much more expensive to run than BRI and is not
commonly selected by individual remote access users. In most cases,
BRI is preferred when using ISDN for remote access.
Digital Transmission
ISDN
is a digital transmission, as opposed to the analog transmission of
PSTN. ISDN lines must be used at both the server and remote site. In
addition, you must install an ISDN modem in both the server and the
remote client.
Extends over Local Telephone Exchange
ISDN
is not simply a point-to-point connection as a leased line. ISDN
networks extend from the local telephone exchange to the remote user
and include all of the telecommunications and switching equipment
lying between them.
ISDN Modem
Dial-up remote access equipment consists of an ISDN modem each for
the remote access client and the remote access server. ISDN offers
much faster communication than PSTN, communicating at speeds of 64
Kbps or faster.
