Local Analysis of Structural Limitations of Network Congestion Control

Recently there have been a number of interesting contributions to the stability analysis of network congestion control based on fluid models. Here, we further this emerging analysis by studying the structural limitations that so called primal/dual congestion control algorithms impose. Such algorithms rely on aggregated information from a network path, e.g. TCP-Vegas use the aggregated queuing delay. We show through local analysis that this imposes certain limitations of feedback control. Viewed from the source side, the complementary sensitivity and the sensitivity functions are severely restricted when many sources share the same bottleneck. This impose that source control must be small enough to achieve suitable noise rejection. In addition, a specialized congestion control paradigm where all sources share a common time-base is analyzed. For this scenario the analysis facilitates significantly and robustness limitations towards configuration changes is observed.