ISDN

What does ISDN stand for? It is the Integrated Services Digital Network that comprised of digital telephony and data-transport services offered by regional telephone carries. ISDN involves the digitalization of the telephone network, which permits voice, data, text, graphics, music, video and other source material to be transmitted over existing telephone. The emergence of ISDN represents an effort to standardize subscriber services, user/network interfaces, and network and inter-network capabilities. ISDN applications include high-speed image applications, additional telephone lines in home to serve the telecommuting industry, high speed file transfer, and video conferencing. Voice service is also an application for ISDN.

How Integrated Services Digital Network Works?

ISDN is a broadband service provides end to end digital communication for high speed data supporting voice, video and multimedia applications. Broadband as compare to Base-band is a type of service that supports logical channels. ISDN BRI and ISDN PRI are two services of ISDN technology used worldwide.

The ISDN BRI (Basic Rate Interface) offers two B channels and one D channel (2B+D). BRI B-channel service operates at 64 kbps and is meant to carry user data; BRI D-channel service operates at 16 kbps and is meant to carry control and signaling information, although it can support user data transmission under certain circumstances. The D channel signaling protocol comprises Layers 1 through 3 of the OSI reference model. BRI also provides for framing control and other overhead, bringing its total bit rate to 192 kbps called isdn 2. The BRI physical-layer specification is ITU-T formerly the CCITT 1.430.

ISDN PRI (Primary Rate Interface)

Service offers 23 B channels and one D channel in some regions like North America and Japan, yielding a total bit rate of 1544 kbps including the PRI D Channel runs at 64 kbps. In Europe, Australia, and the other parts of the world ISDN PRI provides 30 B channels plus one 64-kbps channel with a total interface rate of 2048 kbps called isdn 30. The physical-layer specification of PRI is ITU-t 1.431.

In India ISDN PRI offers 30 B Channels of 64kbps each.

ISDN Hardware Components

ISDN components include terminals, terminal adapters, network-termination devices, line-termination equipment, and exchange-termination equipment. ISDN terminals come in two types. Specialized ISDN terminals are referred to as TE1 (terminal equipment 1). Non-ISDN terminals, such as DTE, that predate the ISDN standards are referred to as TE2 (terminal equipment type 2). TE1 connects to the ISDN network through a four-wire, twisted-pair digital link whileTE2 connects to an ISDN network through a Terminal

Adapter (TA). The ISDN Terminal Adapter can be either a standalone device or a board inside the TE2. If the TE2 is implemented as a standalone device, it connects to the Terminal Adapter via a standard physical-layer interface for example EIA/TIA-232-C (formerly RS-232-C), V.24, and V.35.

Beyond the TE1 and TE2 devices, the next connection point in the ISDN network is the NT1 (network termination type 1) or NT2 (network termination type 2) device. These are network-termination devices that connect the four-wire subscriber wiring to the conventional two-wire local loop. In North America and Japan, the NT1 is the CPE (customer premises equipment) device. In Europe and most of the other parts of the world, the NT1 is part of the network provided by the carrier. The NT2 is a more complicated device that typically is found in digital PBX (private branch exchanges) and that performs layer 2 and layer 3 protocol functions and connection services. An NT1/2 device also exists as a single device that combines the functions of an NT1 and NT2.

Followings are the some important functions or hardware of ISDN.

Benefits -

1. Single connection can support both voice and data.
2. High quality services being digital right from subs, premises (End to End).
3. Eight terminals can be connected on a single line.
4. High speed data transfer from PC to PC is possible 64 Kbps against existing 9.6 Kbps (6 times faster).
5. Two calls can be established simultaneously on a single pair of wires.
6. The call set time is very short (1-2 seconds).
7. A number of supplementary services are supported like in pots.
Calling Line Identification, Call Forwarding, Call Forwarding on busy signal, Call Forwarding on no reply, Call Forwarding unconditional, Advice of Charge, Terminal Portability, Multiple Subscriber Number, Closed User Group.

ISDN Feature Phone : This terminals, in addition to having a handset and dialing key pad, also has a LCD display , additional keys for storing frequently dialed numbers & other function keys.

Terminal Adaptor : The existing terminals like rotary telephone, push button telephone, personal computer , G-3 fax machine etc. can be connected to the ISDN line through a terminal adaptor (TA). The terminal adaptor provides connectivity to ISDN line on one side. On the other side a number of connections are possible to which various types of existing equipment described above can be connected.

1) Analogue Connector : Rotary telephones, push button telephones (pulse type or tone type), fax, answering machines, cordless phones etc. can be connected to this port /connector.

2) Data Port : Any PC with RS 232C connection (serial port of the PC) can be connected to this port, Data transfer using standard software packages like X talk or ProComm is possible up to 9.6 Kbps. Modem is not required.

Video Conferencing : The professional specialized Video Conferencing Camera will be connected to the network model using 4 ISDN lines. The Camera establishes connection to a similar Camera connected to the ISDN network across the Globe on the other side by dialing through the ISDN network. Once the Call is established using the Remote control panel, the video camera can be moved or zoomed on the required participants of the conference. The transmitted picture can be viewed along with the received picture.

Moving images (Video) of the conference participants can be sent as well as received along with their conversation (Audio). It is possible to send power Point Presentations, diagrams and photographs by a still picture camera during the Conference to the far end. Data transfer can also be done simultaneously. Depend upon the Make and Model of the Camera the Device and work from 128 kbps to 768 kbps.

Video Phone : This is a low cost, compact version of the video conferencing equipment. The equipment consists of a compact screen with a camera . This requires only one ISDN line. Video images and conversation are sent and received at 128 kbps.

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