Boundedness of Heterogeneous TCP Flows with Multiple Bottlenecks

TCP has been the dominant congestion control protocol in the Internet. Although it is well known that TCP combined with intermediate systems with active queue management (AQM) schemes can not guarantee asymptotical stability when the feedback delay or the link capacity is large, the asymptotical stability may not be necessary for network achieving good performance in terms of resource utilization, flow throughput and queueing delay. Practical bounds are important performance index for congestion control protocols and AQM schemes. How to derive practical bounds for realistic systems with heterogeneous flows, various delays and multiple bottlenecks is an important and challenging open issue. In this paper, we study the boundedness of generalized TCP and AQM systems considering the heterogeneity of flows and the impact of multiple bottlenecks. We derive the uniform bounds and uniform ultimate bounds of flow window size, which reveal how the system and flow parameters affect the system performance. Extensive simulation results have been given to verify the correctness of the bounds.