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Collaboration, Voice & AV · Intermediate

Erlang

A unit of telephone traffic equal to one circuit continuously occupied for one hour, used for trunk and staffing calculations.

Definition

Traffic in Erlangs equals call arrival rate times average holding time; for example 30 calls per hour averaging 4 minutes equals 2 Erlangs. One Erlang equals 36 CCS (hundred call seconds). The busy hour traffic value is used with Erlang B for trunk sizing and Erlang C for agent staffing.

Example

120 calls in the busy hour lasting 3 minutes each produce 6 Erlangs of traffic.

Exam tip

Erlang B assumes blocked calls are lost (trunks); Erlang C assumes callers wait (queues/agents).

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