What is background traffic in a network simulation?

A background traffic is nothing but another traffic which is used simultaneously along with the primary traffic of interest.

For example, if you need to evaluate the performance of your custom voice over IP (VoIP) application, then it may use tcp or sctp  to transport your voice. But in ideal network condition, you will have all the necessary network resources and bandwidth so that you can not prove that your VoIP application will work better even in worst network condition. So, for that, you have to simulate the worst network condition with some “bottle necks” and “traffic overheads”.  For that purpose, another traffic is needed – Such background traffic may use any kind of transport agent (tcp, udp, etc.,) and may use any kind of application (cbr, vbr, telnet, ftp, etc.,)

So, for example, if you need to evaluate the performance of your VoIP application protocol with respect to different network load condition, you may do it in different ways.0

(1) Run the simulation with different background traffic conditions (against 5, 10, 20, background cbr flows) and how your fixed number of VoIP flows getting affected by such background traffic condition.

(2) Or, without any such background traffic, simply you may run the simulation with different number of VoIP flows (5, 10, 20, .. VoIP flows) and evaluate its performance

Generally, researchers prefer combining (1) and (2) to do a good evaluation while evaluating their new protocol.