Saturday, 24 October 2009

Switching and some history

Before solid state digital electronic devices became available circuit swithed network technology used analogue electronics operating with variables represented by continuously measuring voltages and other quantities.

How a microphone works:
Microphones are an example of a device that changes information from one form to another. Sound information exists as patterns of air pressure; a microphone changes the information that makes the patterns what they are into patterns of electric current.

In 1960
Many companies started to use computers to manage and organize their business. Thus a network was needed for these different computer terminals to communicate with each other and transmit data.

Data was first encoded in the same way that the voice networks encoded sounds. The data was sent over conversional telephone circuits. The devises used to convert data from digital to analogue signals appropriate for telephone circuits are called modems. The 1st modems operated at rates of 110 bits per second. With in 5 years they had reached speeds of 300 to 1120 bits per second. Today, bandwidth of a typical copper line reaches 56kbps (56000 bits per second).

Processor and memory technologies developed throughout the 60's becoming faster and more capable to deal with more signals. Circuit-switched communication was not able to catch up. The US DOD became aware of the potentials of strategy planning through this technology. The circuit switched technology prevented them from using hight speed computers and so ARPA (Advanced Research Projects Agency Network) worked on developing better communications technologies. Resulting in a simple solution of allowing many computers to share the circuit so each individual one receives a part of the total capacity, making packet switching switching automatic and fair. In this solution data had to be divided into packets. The network accepts packets from multiple senders each with its own destination in a header. Then routes them to their respective destinations. The need for better communication networks stimulated much of the research, Bell Labs being a pioneer.

In 1991
Packet switching data network ARPANET celebrated its 20th anniversary, faster high speed communications became more popular and the original ARPANET with its network address was discontinued.

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