ASYNCHRONOUS TRANSFER MODE(ATM)

ATM i.e. Asynchronous Transfer Mode is a streamlined transfer interface. It also is a connection oriented network and uses packets of fixed sizes for communication of data. These fixed size packets are called cells. This technique is used for efficient data transfer over high speed data networks. It provides real time and non-real time both services.

It requires an adaption layer for supporting the information transfer protocols that are not based on ATM.

APPLICATIONS :-

• It was developed as a part of of work on ISDN.
• Now, it is also used in non ISDN systems where the data rates are very high.

CELL RELAY:-

As mentioned, the system uses packets of fixed length ,called cells, for data transmission. The cell relay provides a small number of bits for the purpose of error control.The number of bits depends on the inherent capability of the transmission  system.

Due to fixed length packets, the processing overhead is reduced . Therefore it is designed to work in the range of 10 to 100 of Mbps.

By using small, fixed length cells, the it becomes so efficient that it can offer a constant data rate even though it is using a packet switching technique.

Thus , using this system, it is possible to allow multiple channels with the data rate of each channel dynamically set on demand.

ATM VIRTUAL CIRCUITS:-

ATM networks are connection oriented.  Hence before sending data, first, it is necessary to send a packet to set up a connection.

The setup packet passes through the subnet. All the routers on it’s path make entry into their table about this new connection.  These connections are called virtual circuits.

Most ATM networks also support the permanent virtual circuits. They are permanent connections between two distinct hosts.

Once the connection is established , both the sides can start transmitting the data.

ATM CELL:-

In ATM , the Information is transmitted in the form of small packets of fixed size. They are called ATM cells.

Each ATM cell is 53 byte long with 5 bytes for header and 48 bytes reserved for data.

All the cells follow the same root to destination.

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