Introduction to Congestion Control

What Is Congestion?

When more packets than the network has bandwidth for are sent through, some of them start getting dropped and others get delayed. This phenomenon leads to an overall drop in performance and is called congestion.

This is analogous to vehicle traffic congestion when too many vehicles drive on the same road at the same time. This slows the overall traffic down.

How Do We Fix It?

Congestion physically occurs at the network layer (i.e. in routers), however it’s mainly caused by the transport layer sending too much data at once. That means it will have to be dealt with or ‘controlled’ at the transport layer as well.

Note: Congestion control also occurs in the network layer, but we’re skipping over that detail for now since the focus of this chapter is the transport layer. So congestion control with TCP is end-to-end; it ...