Asynchronous transfer mode (ATM)

Asynchronous transfer mode is a connection-oriented network. Here transmission is not synchronous. This was designed and introduced in the year 1990. ATM is effective in merging voice, data, cable television, telex, telegraph etc. and thus forming a single integrated system. ATM is widely used in the telephone system for moving IP packets. ATM networks support permanent virtual circuits which are permanent connections between two hosts. ATM transmits information in the form of small packets called cells. These cells are 53 bytes long. Here 5 bytes are header and remaining 48 bytes are payload. Part of the header is the connection identifier which allows each router to identify incoming cell. ATM hardware is capable of setting up one incoming cell to multiple output lines. This allows broadcasting of television program to multiple viewers. Since small cells do not block any line, quality of the service is guaranteed. ATM reference model is different from OSI model and TCP/IP model and consists of three layers. The ATM layer deals with cells and transportation of cells. ATM adaptation layer divides the packets and transmits the cells. The physical layer deals with voltages and bit timing. The ATM adaptation layer is further divided into segmentation and reassembly sublayer and convergence sublayer.