Integrated Services Digital Network, which is
commonly termed as ISDN,
is a set of communication standards for synchronized digital
broadcasting of various network services like voice, video and data over the
conventional telephone network. Its definition first appeared in the red book
by the International Telegraph and Telephone
Consultative Committee (CCITT) in 1988. Before
ISDN came into existence, the telephone network was seen as a medium
to transport voice, with only some services at offer for data. The main
characteristic of ISDN is that it incorporates speech and data on same line;
thus, adding special features that were not available in the traditional telephone system. The ISDN
standards explain various types of access interfaces, like Basic Rate Interface
(BRI), Primary Rate Interface (PRI), Narrowband ISDN (N-ISDN) and Broadband
ISDN (B-ISDN).
PRI line is a single wire line connection that connects the server in
office with the telephone exchange of an organization. Although, PRI is a
single line having single number, but it has upto 30 separate channels, which
enables connecting 30 distinct telephone sets to one PRI line using an EPBX
device; therefore, permits 30 calls simultaneously. Third party vendors that
provide call center
services use PRI lines.
ISDN is a network system that employs circuit-switched telephone network
system. It provides access to packet switched networks, which are usually
designed to permit digital transmission of voice and data over conventional telephone wires. As a result, it
provides better voice quality than an analog phone.
ISDN provides circuit-switched connections for voice and/or data and
packet-switched connections for data in increments of 64 kilobit/s. In recent
times, ISDN has found large market application for Internet access. In terms of
Internet and bandwidth, ISDN can provide a maximum of 128 kbit/s bandwidth. To
overcome this limitation, Channel bonding is employed as it enables to achieve
greater data rate. In Channel bonding, ISDN B-channels of three or four BRIs are
bonded together. In a video conference
setting, ISDN delivers synchronized voice, video and text transmission between individual
and group of video conferencing systems.