Optimizing the cost of migration from wireless tdm networks to next generation packet networks

Abstract

The major wireless operators are actively migrating their networks from circuit switched networks to all packet (IP) based next generation networks. One of the key issues impeding the migration is the associated cost. Though managing the CAPEX (CAPital EXpenditures) and OPEX (OPerational EXpenditure) has been the focus of the operators, minimizing the cost from the perspective of system design has received relatively less attention. In this paper, we investigate a particular trunk allocation problem in a circuit/packet hybrid switch to show how system and algorithm design can significantly reduce the migration cost, so that the operators achieve cost effective migration. In such a problem, allocating different trunk types to the two legs of a call/session results in utilization of a special hardware - an interworking unit to bridge the two types of trunks (TDM and IP) so that the call can be completed. The interworking unit is costly to the operators since it is a pure migration cost with no value after the migration. The key to minimize such cost lies in algorithm design to minimize the traffic requirement of the interworking unit, which is a challenging task due to the complexity of the problem. We develop an analytic model to characterize the traffic over the interworking unit in a hybrid switch with both packet and circuit trunk resources. The system is decoupled into two subsystems, each of which is modeled as a two-dimensional Markov chain. Exact solution of the model is provided through a recursion, and an iterative algorithm is developed to eliminate the difficulty in finding the solution for a large scale system. The accuracy of the iterative algorithm is verified by the simulation results from a OPNET simulation model. The numerical results show the algorithm is very accurate. It can be used to optimize the system resource provisioning and traffic distribution for minimizing the bridged traffic in a hybrid switch. Our results demonstrate it can provide significant cost and performance benefit during migration from TDM networks to next generation packet networks.