In the general distribution models below,
denotes the mean of the distribution and
the variance.
Kendall Notation for Queue  Server Utilisation  Average Customer Wait Time (W_{q})  Average Length of Queue (L_{q}) 

M / M / 1  
M / M / n  Not available as a general formula.  
M / D / 1  Not available as a general formula.  
M / D / n 


M / E_{k} / 1  
M / E_{k} / n 


M / G / 1  Not available as a general formula. 
Historical Note: The formula for Lq (or Wq) for the M / G / 1 model is called the PollaczekKhintchine formula, named after it's discovers. The formula is very useful  it is remarkably simple for such a generalised model. The formula for the M / D / 1 is also derived directly from this formula  it is a special case where the variance is equal to nil.
Other models also exist, but in most other cases apart from those tabulated
above, formulae are too complex to consider here. However, methods of obtaining
numerical results for most queueing problems exist, even if general formulae
do not. [KLEI75] covers many diverse
models.