Comparison of loss formulas for a circuit group with overflow traffic

Many articles have dealt with the loss formulas for determining the required number of circuits in a transit circuit group with overflow traffic. Traditionally, ERM (Equivalent Random Method) is used to determine number of circuits in a final circuit group with rough overflow traffic which has vmr (variance to mean ratio) greater than one. Recently, IPP (Interrupted Poisson Process) approximate method which represents the collective feature of the overflow have been introduced. The negative binomial loss formula can be applied to determine the required number of circuits. In this paper, we deal with the negative binomial loss formula and determination method of number of circuits. We also analyze and compare these three loss formulas. To apply these formulas to the capacity planning of circuit networks, we need more effective algorithm for the accurate numerical calculation.