Additional Switching Nodes: Not a Panacea for Congested Wireless Networks

Traditionally, service providers have been adding Mobile Switching Centers (MSCs) in their wireless networks whenever the switches run out of capacity. In a recent analysis of a large metroplitan network, we observed something seemingly counter-intuitive: additional MSCs do not necessarily add subscriber capacity and they can sometimes even cause decreased network capacity. The apparent anomaly can be intuitively explained by noting that the subscriber capacity of a network is a function of both its call-processing capacity as well as mobility-handling capacity. A new MSC in a network will always add call-processing capacity but additional MSCs will also result in increased inter-MSC signaling for mobility handling. Exhaustion of signaling capacity may offset any benefit of the additional cell-processing capacity of the new MSC. In this paper, we establish a methodology for predicting capacity exhaust in an expanding network and also present practical suggestions for avoiding network congestion. Even though the analysis was done for a network with traditional monolithic switches, the methodology can be applied towards next generation distributed architectures as well.