Flows: how they compete for network resources
Written by Leonardo Balliache

This document will try to explain how flows (TCP and/or UDP) interact between them when they share the same link and are subjugated to different conditions. Because it is very difficult to make tests using a real network, and also because the ns-2 network simulator has proved to be an excelent tool for simulating network behavior, we will use this simulator for our tests.

It is very important to understand the inner behavior of flows when they are competing for scarce network resources. This knowledge will provide us with a better understanding of how flows fight for having an space in the network and how this fight affects their performance.

Let's start with this as soon as is possible, but before, a warning: this is not, again, this is not an ns-2 tutorial or something like an ns-2 tutorial. I haven't as a goal to explain how to deal with ns-2. Go to the ns-2 site above to understand how to use the tool. My goal is to concentrate our attention in flow behavior when they compete for network resources. The tcl code required to feed the ns-2 simulator is just presented, but not discussed. Of course, if you catch me an error in the code, make me know ASAP; I'm a human being and can be wrong.
Having said this, let's begin our work. Just below is an index:

1.0.- One TCP flow

2.0.- One UDP flow

3.0.- Two TCP flows

4.0.- Two UDP flows

5.0.- One TCP flow and One UDP flow