We consider the behavior of generalized TCP congestion avoidance when subject to randomized congestion feedback, such as RED and ECN. The window distribution of individual flows under a variable packet loss/marking probability is established and studied to demonstrate the desirability of specifying a less drastic reduction in the window size in response to ECN-basedcongestion feedback. A fixed-point based analysis is presented to derive the mean TCP window sizes and the mean queue occupancy when multiple such generalized TCP flows interact with a single bottleneck queue performing randomized congestion feedback. Recommendations on the use of memory (use of weighted averages of the past queue occupancy) and on the use of "drop-biasing" (minimum separation betwen consecutive drops) are provided to reduce the variability of the queue occupancy. Finally, the interaction of TCP congestion avoidance with randomized feedback is related to a framework for global optimization of network costs. Such a relation is used to provide the theory behind the shape of the marking (dropping) functions used in a randomized feedback scheme.
(* Joint work with Archan Misra and Teun Ott of Telcordia Research)
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