Throughput analysis of Scalable TCP congestion control

Scalable TCP (STCP) has been proposed a congestion control algorithm for high speed networks. We present a mathematical analysis of STCP´s congestion window through the slow start and the congestion avoidance phases. We analyse the evolution of congestion windows for single and multiple flows and for DropTail queues with and without random loss. We derive throughput formulas for the different setups and reveal the inherent unfairness between different round trip times flows. Our mathematical analysis is compared to state-of-the-art network simulator (ns) results, which verifies our model´s accuracy. With our analysis we want to adaptively control STCP´s fixed parameters in order to overcome the fairness problems. These experiments are work in progress and will be presented in a sequel paper

Fairness in MIMD Congestion Control Algorithms

We study in this paper the fairness in throughput among two sessions that share a common bottleneck link, where one or both of the sessions use a multiplicative increase multiplicative decrease (MIMD) algorithm. Losses or congestion signals occur when the capacity is achieved but could also be initiated before that. Both synchronized losses as well as non-synchronized losses are considered as well as their combination. In the non-synchronized case, only one session suffers a loss. Two types of models are then considered to determine which of the source looses a packet: a rate dependent model in which the loss probability of a session is proportional to its rate at the congestion istant, and the independent loss rate model. We first study how two MIMD sessions share the capacity in the presence of general combinations of synchronized and nonsynchronized losses. We show that, in the presence of rate, dependent losses, the capacity is fairly shared between the two sessions where as loss independent rate provides high unfairness even when sessions are symmetric. In the second part we study how the capacity is shared among several sessions, each of which either uses an additive increase multiplicative decrease (AIMD) or a MIMD algorithm in presence of synchronized losses. We show that the AIMD session obtains a share which is independent of the link capacity, and that the rest of the capacity is utilized by the MIMD session