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Reply To: Erlang Formula

Lee Ann

You have to pick a Grade of Service or acceptable level of congstion to derive channels needed (usually 1 to 5% and also known as probibility). I use P.01 (1% GOS) for trunks and P.02 (2% GOS) for wireless voice paths, plus decide on a utilization % to be ahead of the curve (80 to 95% utilization means I take the erlang divide by .8 or .95).

55 erlang,
at 100% utilization (what you requested) for 2% GOS = 66 voice paths; for 3% GOS = 63; for 4% = 61; for 5% = 60.

Erlang B defined: A probability distribuiton developed by A.K. Erlang to estimate the # of telephone trunks needed to carry a given amount of traffic. Erlang B assumes that, when a call arriving at random finds all trunks busy, it vanishes. Erlang B is used when the traffic is random and there is no queuing.

Lee Ann Jones
Network Traffic Planning Engineer