The Extended Erlang B Traffic Model

The Extended Erlang B Traffic Model is an analytical model for calculating call blocking.

The model makes the following assumptions:

•	Calls are presented randomly to a trunk group (Poisson arrivals).

•	Call times are fixed or are exponentially distributed.

Unlike the Erlang B Traffic Model, the Extended Erlang B Traffic Model takes into account the extra traffic offered to a trunk group caused by retries; that is, calls which are immediately redialled because they were blocked.

This traffic model may be applied to situations in which no overflow facilities exist.