What is Integrated Services Digital Network (ISDN)?

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.