Wikipedia: Traffic engineering

Traffic engineering describes the use of statistical techniques such as [queuing theory]? to predict and engineer the behaviour of telecommunications networks such as telephone networks or the Internet.

The field was created by the work of A.K. Erlang in whose honour the unit of telecommunication traffic, the Erlang is named.

The crucial observation in traffic engineering is that in large systems the [law of large numbers]? can be used to make the aggregate properties of a system over a long period of time much more predictable than the behaviour of individual parts of the system.

The techniques originally developed for circuit-switched? networks have now been extended to packet-switched? networks.

In the two sub-fields, the traffic engineering term "Quality of Service" means two related but distinct things. In circuit-switched networks it refers to the probability of being able to initiate a call to another party. In circuit-switched networks it refers to the probability of the network meeting a given [traffic contract]?, or in many cases is used informally to refer the probability of a packet passing between two points in the network.