# Paper Review: General AIMD Congrestion Control

# Reviewer: Mark Meras (mm446)

## Main Contribution

This paper by Yang and Lam discusses a new analysis of the additive
increase/multiplicative decrease congestion control algorithm present in
TCP. Their analysis generalizes the AIMD algorithm into the GAIMD
algorithm (General AIMD) and shows that the parameters of the GAIMD can be
set so that the congestion control is TCP friendly.

## Key Ideas

- We can generalize the AIMD scheme by adding two variables that
control the two aspects of AIMD:
- alpha - the increase in the window size if there is no packet loss in
round-trip time
- beta - the fraction of the window size that it is decreased to when
packet loss is detected

- A simple formula can be derived for the average sending rate of a
flow controlled by GAIMD. This formula is a function of alpha, beta, loss
rate, average RTT, average timeout value, and the number of packets
acknowledged per ACK. This formula is validated up to 20% loss rate.
- A relationship between alpha and beta is determined so that the
resulting congestion control is TCP-friendly. This formula is: alpha = (1
- (beta * beta)) / 3

## Critique of Contribution

- This contribution is very important, as it provides and
experimentally verifies two new formulae for calculation the mean sending
flow rate as well as the relationship between alpha and beta
- More importantly, the paper introduces and validates a general AIMD
congestion control mechanism and shows it to be effective and TCP-friendly

## Lesson

We can get better perfomance by generalizing the AIMD and tuning its
parameters.

## Open Question

What are the tradeoffs among rate fluctuations, responsiveness, and speed
of convergence?