Dimensioning Trunk Groups for Digital Networks

Dimensioning Trunk Groups for Digital Networks ByW. B. ELSNER (Manuscript received January 22, 1980) The use of digital switching and transmission facilities in the metropolitan environment is expanding rapidly. Since these facilities must be installed in multiples of 24 circuits, their per-trunk cost is nonlinear. Traditional methods for dimensioning high-usage trunk groups, however, assume linear facility costs and thus lead to nonoptimal network designs. An approximate method for dealing with nonlinear trunk costs is modular engineering, i.e., the sizing of trunk groups in multiples of a fixed module size. We examine the cost benefit of modular engineering for digital networks by simulating the traffic and facility provisioning processes for a representative city. Results show that sizing one-way high-usage groups in modules of 12 trunks and two-way groups in modules of 24 saves 4 to 9 percent of total network first cost relative to the nonmodular alternative. Administrative costs are also reduced through a decrease in the number of high-usage groups. The results are robust to network structure and growth, facility costs, forecast error, and accelerated switch exhausts.