Explicit calculation of overflow variances in loss systems with selective trunk reservation

In this paper, systems with selective trunk reservation are investigated. A (primary) group with two offered traffic streams is considered. For the high-priority traffic the trunk group acts as a group of full accessibility. Calls of the low-priority traffic can only be switched if more than a number of nres trunks (nres trunks are reserved for the high-priority traffic) are idle. In the paper, explicit formulae for the variance of the low-priority overflow traffic and of the total overflow traffic are presented (formulae for the high-priority overflow traffic have been published earlier [Schehrer R. On the explicit calculation of overflow moments of the high-priority traffic in loss systems with selective trunk reservation. In: 19th international teletraffic congress, Beijing: Beijing University of Posts and Telecommunications Press; 2005. p. 1029-38]). The calculations are carried out in terms of factorial moments.