other queuing and staffing models

As well as the Erlang C model there are several other call center staffing and queuing models in use.

simulation

This is the most accurate way of modeling as it simulates a 'real' call center with thousands of calls arriving and being handled, using a 'Monte Carlo' simulation. It can also handle a mix of call types, call priorities and agent skills, along with accurately calculating expected abandonment rates.

cc-Modeler Professional is the only low-cost call center tool that includes a simulation module.

'merlang'

Merlang (or modified erlang) is an attempt by one vendor to overcome two of the restrictive assumptions of the Erlang C model. It adds another two parameters to the calculations - 'Mean time to abandon' (or MTA) and 'Expected Retry Percent'.

However there are several obvious issues with this approach -

Parameter

Notes

Mean Time to Abandon

This is not available from any ACD statistics and must simply be guessed.

There is actually no such thing as a 'mean' time to abandon - some callers hang up immediately on reaching the queue; others will hang on virtually forever. The relationship between abandonment rate and time on hold is quite complex and varies very much by the type of caller, the nature of their problem and their expectations. It is not simply a straight line relationship.

The result is that any estimated MTA probably has an accuracy of no better than 20%. (Actually improving the 'Wrapup Time' parameter has a much greater impact than attempting to include a MTA).

(In contrast, the cc-Modeler 'Simulation' module allows you to use actual ACD data as its inputs to calculate abandonment rates).

Expected Retry Percent

This is the percentage of callers who, after abandoning, will call again some time later.

It can only be guessed at.

In addition, retries will generally arrive in a later 'interval' - this is not handled by Merlang.

This model also does not address another Erlang assumption of a 'steady state' situation where all calls are handled in the same interval in which they arrive (i.e. there is never any backlog of calls impacting subsequent time periods).

Our conclusion is that in trying to solve one problem, Merlang actually introduces several others.