Posted By: technopediasite
Downfall of ATM (Asynchronous Transfer Mode) in Telecom Networks


In fact, ATM was very capable of performing the functions. An ATM stream at any SONET/SDH compatible rate could carry dozens, hundreds or thousands of individual customer circuits, constantly shifting and prioritizing to squeeze out every last possible drop of bandwidth. ATM networks automatically compensated for number two above with the same function of constant shifting/prioritizing. If a daytime customer did not send any data during the night, he automatically did not use any bandwidth. Regarding number three above, there was an organized hierarchy of monitoring that would make it very easy to locate trouble in the imagined future network.

The Downfall of ATM

Why didn’t ATM solve all the shortcomings and take its rightful place as the ubiquitous data format carried on SONET/SDH?There is no certain answer to this question. However, there are at least two significant factors that clearly had an effect. First is that ATM itself is not very efficient in its use of bandwidth. In ATM all payload data is separated into groups of 48 bytes called “cells”.Each of the cells has a 5-byte header. The header is overhead. Right away, almost 10% of the bandwidth is lost. Certain types of data required even more ATM overhead. The second factor is just plain marketing. While not really being direct competitors, other protocols which performed some ATM-like functions crept in and grabbed market share. This includes IP, PPP and many others. Companies who bought into any particular protocol were unlikely to change.
Downfall of ATM
ATM, intended as “the” format for data transfer, quickly became “one of ” and interestingly enough was not in the favored category. IP, with its variable packet size and more efficient use of bandwidth, has emerged as one of the winners. Other protocols are common as well and must be carried by the networks of today.

ATM is not dead but is not implemented broadly enough to fulfill its intended role. Government had a hand in the development of ATM and remains one of its largest users. When we saw pictures of the Martian landscape, they had traversed millions of miles in the form of ATM cells. Battlefield pictures in real time are transported daily around the world using ATM. Yet, for most networks, ATM will not come to the rescue.

What is ATM (Asynchronous Transfer Mode)

Asynchronous transfer mode (ATM) is a switching technique used by telecommunication networks that uses asynchronous time-division multiplexing to encode data into small, fixed-sized cells. This is different from Ethernet or internet, which use variable packet sizes for data or frames. ATM is the core protocol used over the synchronous optical network (SONET) backbone of the integrated digital services network (ISDN).
ATM  bit rate choices:
➤Available Bit Rate: Provides a guaranteed minimum capacity but data can be bursted to higher capacities when network traffic is minimal.
➤Constant Bit Rate: Specifies a fixed bit rate so that data is sent in a steady stream. This is analogous to a leased line.
➤Unspecified Bit Rate: Doesn’t guarantee any throughput level and is used for applications such as file transfers that can tolerate delays.
➤Variable Bit Rate (VBR): Provides a specified throughput, but data is not sent evenly. This makes it a popular choice for voice and videoconferencing.