Analysis of the Increase and Decrease Algorithms for Congestion Avoidance in Computer Networks

Summary

The authors in this paper aim to find the "best" congestion avoidance algorithm. The criteria they use to measure an algorithm are efficiency, fairness, convergence, time and size of oscillations. Congestion avoidance algorithms aim to keep the load oscillating around the "knee". They try a set of algorithms which fall under "increase/decrease" algorithms using a binary feedback scheme. This means that the sender will only get feedback about whether the network is overloaded or not. If the sender gets feedback that the network is overloaded, the sender should decrease the packets its sending and similarly if the network is not overloaded. The 4 main combinations that the authors test are 1) additive increase, additive decrease 2) additive increase, multiplicative decrease 3) multiplicative increase, additive decrease and 4) multiplicative increase, multiplicative decrease. The authors then lay out a mechanism to determine if and when a control converges to efficiency. Then, they figure out which policy of the 4 listed above minimize convergence time and the oscillations that occur. They conclude that additive increase with multiplicative decrease is the optimal policy when considering efficiency and fairness.

Criticisms & Questions

One assumption that the authors make is that "all users receive the same feedback and react to it". I would like to know if this assumption holds in the real world. I'm curious to find out if senders are always required to follow congestion control feedback or if there are ways to bypass them. And, if it is possible to bypass them, are there mechanisms in the congestion control protocol that would be able to control these uncooperative senders?

Feedback

I really liked this paper. It was easy to read and very clear in laying out their plan and their logic.