Atm network
Atm networkThe Asynchronous Transfer Mode has been chosen as the standard system concept for integrated broadband communication networks by the ITUT. The system is predicted to grow rapidly as soon as it becomes widely accepted by network operators and users. Why has communications evolved in history towards the ATM concept and why has it been chosen as the broadband solution?
In the late 1800's public telephone networks capable of transmitting analogue voice signals were established. The users were connected together via switches across the network to form a circuit. This was the first transfer mode used in telephone networks, and it is known as circuit switching. The invention of the vacuum tube led to the introduction of frequency division multiplexing (FDM) in 1925, and therefore the ability to make multiple connections on a single line. The public switched telephone networks (PSTNs) expanded, but with the circuit switched transfer mode remaining in use. This is because it provided an obvious way of keeping the constant connection necessary for voice traffic.
The invention of the transistor and the concept of pulse code modulation (PCM) allowed digital communications to be developed in the late 1960's. The interconnection of computer systems over telecommunication networks soon became a requirement. Modems were used at first to generate analogue signals compatible with the PSTNs from the digital computer data to allow such interconnections. The already wide spread use of the PSTNs was an advantage of this scheme, however it was soon recognized as not being an optimum solution for data transfer.
The analogue PSTNs were unsuitable in terms of switching, capacity (bandwidth) and channel noise. In data communication applications, data tends to be transferred in bursts, separated by silence. The constant connection provided by circuit switching therefore does not provide optimum usage of the network resources. The PSTNs were ordinally dimensioned to provide capacity to transport voice signals, which provides very limited bandwidth and therefore a low maximum rate of data transfer. The noise present in the PSTNs due to poor channel quality lowers information transfer rates, since redundancy in the data is required to perform error checking.
Solutions for data communications were developed, including the packet switching transfer mode. With this system, the transmitter splits the data to be transferred into discrete units and sends them individually across a network, where at the other end, the data is reconstructed by the receiver. Packets need only be sent when data is available which therefore provides a more optimum use of network resources.
Computer technology advances created the ability for faster information processing and therefore the need for faster communication systems. Specific data networks were introduced such as packet switched data networks (PSDNs), to meet the new service requirements. In the early 1970's, high bit rate digital time division multiplexing (TDM) systems were realized, allowing multiple high speed digital connections on a single line. The requirement for the integration of voice and data signals on a single network emerged....
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