The public telephone system, sometimes
referred to as Plain Old Telephone Service
(POTS), is a
circuit-switched communications network. When a telephone call is
placed in this type of network, only one physical path is used between
the telephones for the duration of that call. This pathway, called a
circuit, is maintained for the exclusive use of the call, until the
connection is ended and the telephone is hung up.
If the same number is called tomorrow from the same location as the call from today, the path would probably not be the same. The circuit is created by a series of switches that use currently available network paths to set up the call end-to-end. This explains why callers can get a clear connection one day, and noise and static on another. This demonstrates that a circuit-switched connection is end-to-end or point-to-point. Conversely, in a packet-switched network,
The difference between circuit and packet switching can be compared to the different ways in which a large group of people traveling from Dallas to San Francisco (two cities in the United States) can reach their destination. For example, circuit switching is similar to loading the entire group on a bus, a train, or an airplane. The route is plotted out, and the whole group travels over that same route. Packet switching is comparable to people traveling in their own automobiles. The group is broken down into individual components just as the data communication is broken into packets. Some travelers can take interstate highways, and others can use back roads. Some can drive straight through, and others can take a more roundabout path. Eventually, they all end up at the same destination. The group is put back together, just as packets are reassembled at the endpoint of the communication.
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no dedicated pathway or circuit is established. When transferring
data, such as a word processing file, from one computer to another
using a packet-switched network, each individual packet (bundle of
data) can take a different route. Although it all arrives at the
same destination, it does not all travel the same path to get
there. This is not the case with a dedicated path or circuit. Internet
traffic uses packet-switching technology.