ISyE Seminar Series - A Mean-Field Model For Multiple TCP Connections Through A Buffer Implementing RED

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Active queue management schemes like RED (Random Early Detection) have been suggested when multiple TCP sessions are multiplexed through a bottleneck buffer. The idea is to detect congestion before the buffer overflows and packets are lost. When the queue length reaches a certain threshold, RED schemes drop/mark incoming packets with a probability that increases as the queue size increases. The objective is an equitable distribution of packet loss and improved network utilization. The window sizes and slow start thresholds of each TCP session evolves like independent dynamical systems coupled by the RED mechanism. Here we introduce a mean-field approximation to one such RED system as the number of flows tends to infinity. The deterministic limiting system is described by a transport equation. The numerical solution of the limiting system is found to provide a good description of the of the evolution of the distribution of the window sizes, the average queue size, the average loss rate per connection and the total throughput. We see that TCP with RED or tail-drop may exhibit limit cycles and this causes unnecessary packet delay variation and variable loss rates. The root cause of these limit cycles is the hysteresis due to the round trip time delay in reacting to a packet loss.


  • Workflow Status: Published
  • Created By: Barbara Christopher
  • Created: 10/11/2010
  • Modified By: Fletcher Moore
  • Modified: 10/07/2016


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