Performance analysis of quantization-based approximation algorithms for precomputing the supported QoS

Precomputation of the supported QoS is very important for internet routing. By constructing routing tables before a request arrives, a packet can be forwarded with a simple table lookup. When the QoS information is provided, a node can immediately know whether a certain request can be supported without launching the path finding process. Unfortunately, as the problem of finding a route satisfying two additive constraints is NP-complete, the supported QoS information can only be approximated using a polynomial time mechanism. A good approximation scheme should reduce the error in estimating the actual supported QoS. Nevertheless, existing approaches which determine this error may not truly reflect the performance on admission control, meaning whether a request can be correctly classified as feasible or infeasible. In this paper, we propose using a novel metric, known as distortion area, to evaluate the performance of precomputing the supported QoS. We then analyze the performance of the class of algorithms that approximate the supported QoS through discretizing link metrics. We demonstrate how the performance of these schemes can be enhanced without increasing complexity. Our results serve as a guideline on developing discretization-based approximation algorithms.