Integrated Service Digital Network

 Integrated services Digital Network(ISDN) is a set of protocol or standards for digital transmission of voice, data, video, and other network services over the traditional circuits of the public switched telephone network.

        
         ISDN was a concept developed by the Consultative Committee on International Telegraph and Telephone (CCITT). The CCIT changed their name to  ITU-T. It is a UN treaty organization. Each country is entitled to send representatives that come from the government that run PTT monopoly to any committee meetings. The name was changed due to the privatization trend separating telephone business from the post office and the general elimination of telegraph service.

Here are some study groups of CCITT with their own area of expertise:

a.)  SG VII on public data networks (X.25) X−series standards

b.)  SG VIII terminal equipment for telematic services

c.)   SG XI ISDN and telephone network switching and signaling

d.)  SG XII transmission performance of telephone networks and terminals

e.)  SG XV transmission systems

f.)    SG XVII data transmission over public telephone networks

g.)  SG XVIII digital networks, including ISDN

     The Basic Rate Interface(BRI) was intended for the standard subscriber interface. It specifies the costumer interface I.45x. It has two bearer channels and a data channel. The costumers’ information is placed on the two bearers’ channels. The concept is that from analog calls to teleconferencing data and these would be switched channels. In the calling party, the analog telephone circuit is digitized to 64kbps at the local Telco office before being switched across the network. It is then turned back into analog at the far end before being delivered to the called party. But now we use two telephone circuits with BRI.

       Here’s a figure that shows the BRI graphically and indicates the bandwidth allocation on the ISDN interface. This is a time-division multiplexed interface where the B,D, and overhead bits are interleaved.

This figure represents the network terminal type of the BRI:

The NT1 creates a four−wire bus called the T interface onto which each ISDN device is connected. It was provided by the Telco as part of the ISDN service.

The NT2 terminal is the device that would do the switching. Allowing the standard eight devices to share the T bus by creating perhaps multiple S buses.

The terminal equipment type 1 (TE1) is a standard ISDN terminal that is

capable of dealing with the B and D channels.

The terminal equipment type 2 (TE2) is a standard device having an RS−232 or V.35 interface. But it doesn't have an ISDN interface capable of handling the D and B channels.

The terminal adapter (TA) is the semi−intelligent device that lets a TE2 connect to the S/T ISDN interface. Its primary function is to run the ISDN interface for our TE2.

Applications of the ISDN interface.

Multiple Channels - Its concept was to provide access to every possible home device and for up to 8 devices using two B channels and one D channels to share among eight devices.

Telephone - From the calling party which is digital instead of being analog from the handset to the central office where it becomes digitized. With ISDN the conversation can be digitized directly from the calling party and passed digitally to the central office and to the called party. It is converted directly into digital at the starting point.

Digital Fax - Fax machines now have to be digital. Therefore, the Group IV fax standard specifies 64 KBps fax operation.

Analog Fax - Analog fax are plug into telephones through a modem that would convert analog tones to digital at 64 KBps.

Computer/Video Conferencing - video conferencing equipment can use one of the 64 KBps or bond both bearer channels together for a 128 KBps digital channel across the network.

Signaling - The function of the data channels is to provide for signaling for setting up and tearing down of the switched bearer channels.

Sources:

1.)  www.wikipedia.com. Issue Date: May 1986 Volume: 4 Issue: 3 On page(s): 320 - 325 ISSN: 0733-                   8716

2.) Future trends R. Aaron, R. Wyndrum, AT&T Bell Laboratories, IEEE Communications Magazine, March 1986, volume 24 #3, pp 38-43. Retrieved 2007-09-02.

3.)   Broadband Telecommunications Handbook second edition by Regis J. Bates.