Dynamics of Congestion Control

Abstract

One reason for the success of TCP and its widespread usage in the Internet is its ability to control network congestion. A TCP source uses implicit notification of network congestion (via packet loss) to control the rate at which it sends data. The rate is controlled by increasing or decreasing the window of outstanding, unacknowledged data. In particular, TCP uses “additive increase and multiplicative decrease” to increase the rate linearly during times of no packet loss, and to decrease the rate geometrically when loss occurs. As a consequence, the rate at which a TCP source transmits tends to be periodic over time. For example, Figure 1 shows the periodic behavior of a single TCP source in an otherwise idle network.

This work was done in collaboration with Youngmi Joo (1970-2001). It is dedicated to her memory.