[ Home ] [ Up ] [ FOOD FOR THOUGHT ] [ SPREAD  SPECTRUM COMMUNICATION ] [ E.S.D ELECTRO-STATIC DISCHARGE ] [ CELLULAR NETWORK SYSTEM ] [ BONE DENSITOMETERS ] [ HUMAN INTELLIGENCE AND THE LAWS OF PHYSICS ] [ ADSL ] [ ONLINE ANALYTICAL PROCESSING (OLAP) ] [ MAGNETIC RESONANCE IMAGING ] [ ATM ] [ PROFILE OF THEMONTH : AIYANGAR  RAMANUJAN ]

ATM:SOLUTION TO BROADBAND ISDN - R. ANANTHANARAYANAN.
                                                                                          NITIN LACHWANI

A Broadband Integrated Services Digital Network (B-ISDN) is a network designed to carry data, voice, images and video. It will offer video on demand, live TV from many sources, full motion multimedia electronic mail, CD quality music, LAN interconnection, high speed data transport for science and industry and many other services, all over the telephone lines!!

B-ISDN accesses data at a very high rate so as to handle image data without delays and planned access rate is 150 Mb/sec.The already available techniques of data transfer such as SWITCHED MULTIMEGABIT DATA SERVICE (SMDS), X.25 networks, frame relay etc. are not capable of transferring data at such high rates.The underlying technology that makes B-ISDN possible is called ASYNCHRONOUS TRANSFER MODE (ATM). It is called asynchronous because it is not synchronous (i.e. tied to a master clock), like most long distance telephone lines are.

The ATM layer provides packet switching capabilities and the ATM adaptation layer, which provides service dependent functions.The basic idea behind ATM is to transmit all information in small, fixed size packets called CELLS. The advantage of fixed sized cells is that it can be switched more efficiently and this results in a very high data rates of ATM.The cells are 53 bytes long of which bytes are header and 48 bytes are payload .

An ATM Cell
The use of cell switching technology has been a gigantic breakthrough. The variety of reasons why cell switching was chosen are:

1. Cell switching is highly flexible and can handle both constant rate traffic (audio, video) and variable rate traffic (data) easily.

2. At very high speeds envisioned, digital switching of cells is easier than using traditional multiplexing techniques especially using fibre optics.

3. For T.V distribution, broadcasting is essential; cell switching can provide this - circuit switching cannot.

PERSPECTIVE:-

ATM promises a unified solution to the diverse fields within the spectrum of communications. Its greatest advantage over other data - transfer technologies lies in its ability to transfer data at an incredible speed of 155 Mbps - 622 Mbps.

As of today, the entire communication network is based on the older circuit switching technology. Changing over to the newer alternative requires co-operation of various industries (television, Internet, telephone companies and computer networks) which is an expensive and time consuming proposition. It will therefor be a while before we can appreciate the advantages of ATM sitting in our homes.

©1999 IEEE VESIT Student Branch  Hits :

Webauthor : Saumitra M Das