Editing Limited availability (section)

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{{Technical|date=September 2010}}
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When customers of a [[public switched telephone network]] make [[telephone call]]s, they utilize a [[telecommunications network]] called a [[Circuit switching|switched-circuit]] network. In a switched-circuit network, devices known as switches are used to connect the [[calling party]] to the [[called party]]. 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. This method is used in, for example graded multiple banks of selectors.<ref>[http://www3.alcatel-lucent.com/bstj/vol50-1971/articles/bstj50-1-135.pdf Inherent Load Balancing] Bell System Technical Journal, Jan 1970, pp 135-165</ref>

In a modern [[circuit-switched]] network, [[Telephone exchange|switches]] can connect any inlet to any outlet; this is known as ''full availability.''