29-04-2014, 04:04 PM
Asynchronous Transfer Mode (ATM)
Asynchronous Transfer.ppt (Size: 1.07 MB / Downloads: 10)
History
ATM is project which is invented by telephone industry in Oct 1991,because after Ethernet was widely installed, the computer industry never stopped its for higher speed network.
The intended speed of ATM network is 155 mbps to 622 mbps with possibility of gigabit speeds later.
Introduction
ATM does not stand for automatic teller machine, In the telecommunication, it stands for Asynchronous Transfer Mode.
ATM is a technology that makes B-ISDN possible.
ATM is standardized technology that enables the convergence of variety of services, low bandwidth and very high bandwidth, synchronous and asynchronous, voice and data, real time and non real time, slotted and packetized.
Types of Traffic and demand on a communication channel
Voice
Its generation is asynchronous (a speaker may speak anytime) .
Its transmission must be synchronous (once the message starts, it must flow continuously as it is spoken) .
The bandwidth required for a voice conversation in digital communication is relatively small and constant (64Kbps) .
The signals may contain a high degree of error and the information can still be retrieved correctly.
Video
The generation is synchronous (continuous).
Its transmission is synchronous. The bandwidth required is variable and it could range from under 64 Kbps to several Mbps in the same session.
Error control should be tight - otherwise the wrong information on the monitor may trigger severe wrongful actions.
Data
Its generation could be either asynchronous (text) or synchronous (telemetry) .
Its transmission in general can be asynchronous (data typically can wait patiently in buffers).
The information is extremely error-sensitive, so extreme caution must be exercised in transmission and error control must be very tight.
ATM Devices
An ATM network is made up of an ATM switch and ATM endpoints.
ATM switch:
An ATM switch is responsible for cell transit through an ATM network. The job of an ATM switch is well defined: It accepts the incoming cell from an ATM endpoint or another ATM switch. It then reads and updates the cell header information and quickly switches the cell to an output interface toward its destination.
Fixed and Small-Sized Packet
Fixed-size cell was preferred over variable sized packet.
ATM was designed for both voice and data communication, it was mandatory to keep transit delay within reasonable bounds.
In this regard, a fixed size cell, as compared to a variable sized packet, offer many advantages like predictable and lesser switching delay and simpler memory-management in switch buffer.
Conclusion
ATM is a technology that can handle all types of traffic ( voice, video and data) multiplexed on the same network. ATM is developed to expedite the process of convergence and provide a synergy between the telecommunication and data communication world.