When customers of the public switched telephone network

Public switched telephone network

The public switched telephone network is the network of the world's public circuit-switched telephone networks. It consists of telephone lines, fiber optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables, all inter-connected by...

 make telephone call

Telephone call

A telephone call is a connection over a telephone network between the calling party and the called party.-Information transmission:A telephone call may carry ordinary voice transmission using a telephone, data transmission when the calling party and called party are using modems, or facsimile...

s, they commonly make use of a telecommunications network

Telecommunications network

A telecommunications network is a collection of terminals, links and nodes which connect together to enable telecommunication between users of the terminals. Networks may use circuit switching or message switching. Each terminal in the network must have a unique address so messages or connections...

 called a switched-circuit

Circuit switching

Circuit switching is a methodology of implementing a telecommunications network in which two network nodes establish a dedicated communications channel through the network before the nodes may communicate. The circuit guarantees the full bandwidth of the channel and remains connected for the...

 network. In a switched-circuit network, devices known as switches are used to connect the caller to the callee. Each switch has a number of inlets and outlets and by connecting a specific inlet to the correct outlet each switch helps to complete an end-to-end circuit between users [1].

In a modern circuit-switched network, switches

Telephone exchange

In the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls...

can connect any inlet to any outlet; this is known as Full Availability.