Monday, 3 October 2011


ATM stands for Asynchronous Transfer Mode. ATM is a connection- orientated technique that requires information to be buffered and then placed in a cell. When there is enough data to fill the cell, the cell is then transported across the network to the destination specified within the cell. We can see that ATM is very similar to packet-switched networks, but there are several important differences: 
ATM provides cell sequence integrity. i.e.cells arrive at the destination in the same order as they left the source. This may not be the case with other packet-switched networks.
Cells are much smaller than standard packet-switched networks. This reduces the value of delay variance , making ATM acceptable for timing sensitive information like voice. 
The quality of transmission likes has lead to the omission of overheads, such as error correction, in order to maximize efficiency.
There is no space between cells. At times when the network is idle, unassigned cells are transported. 
It is these techniques that allow ATM to be more flexible than Narrow-band ISDN(N-ISDN), and hence ATM was chosen as the broadband access to ISDN. The broadband nature of ATM allows for a multitude of different types of services to be transported using the same format. This makes ATM ideal for true integration of voice , data and video facilities on the one network. The flexibility inherent in the cell structure of ATM allows it to match the rate at which it transmits to that generated by the source. Many new high bit-rate services , such as video , are variable bit rate (VBR). Compression techniques create bursty data which is well suited for transmission using ATM cells. 

The ATM networks are likely to be installed by companies that have a specific high bandwidth need. These could include single locations or between buildings. Other solutions are to the joining of LANs exist, such as FDDI, however these solutions are not suitable for the wide area networks (WANs) and the Data must be transformed into something else for transmission. ATM, on the other hand if used through LAN, then the transition to a MAN or WAN would be “seamless” as the same language and technologies would be used throughout. This is an example of the scalability of ATM – the ability to handle different bit rates for different situations and being able to upgrade to higher rates as technology progresses.

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