You may think of circuit switching
as pre-defining the route of a train, before the train actually leaves the station. Once
a circuit is established, it is dedicated and can't be interrupted, until the circuit is
released by one of the end terminals.
The early day telephone exchange was a pure circuit-switched network. In fact, the
circuit-switching device was actually a human operator who connected wires from
one side of the circuit board to the other. Some places in the world still use these old
telephone exchanges, mainly in situations when automatic circuit switching isn't
available. In fact, some armies in the world still use manual switching boards for
field communications??”amazing, isn't it?
Chapter 1
[ 9 ]
A Circuit-Switched Network
A circuit-switched network is usually made up of the following elements??”Central
Office Exchanges, Private Branch Exchanges, and end terminals. Examine the
following diagram:
In the above network diagram, every Central Office Exchange is connected to the
other exchanges. The following diagram can either describe the entire network, or a
small portion of the network, illustrating a single town telephony network. The end
terminals ET1 and ET2 have been assigned numbers 441234567890 and 442234567890
respectively.
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