Simple performance models of differentiated services schemes for the Internet

Schemes based on the tagging of packets have been proposed as a low-cost way to augment the single class best effort service model of the current Internet by including some kind of service discrimination. Such schemes have a number of attractive features, however, it is not clear exactly what kind of service they would provide to applications. Yet quantifying such service is very important to understand the benefits and drawbacks of the different tagging schemes and of the mechanisms in each scheme (for example how much RED with input and output (RIO) contributes in the assured scheme), and to tackle key performance and economic issues (e.g. the difference in tariff between different service classes would presumably depend on the difference in performance between the classes). The goal in this paper is to obtain a quantitative description of the service provided by tagging schemes. Specifically, we describe and solve simple analytic models of two previously proposed schemes, namely the assured service scheme and the premium service scheme. We obtain expressions for performance measures that characterize the service provided to tagged packets, the service provided to non-tagged packets, and the fraction of tagged packets that do not get the better service they were supposed to. We use these expressions, as well as simulations and experiments from actual implementations, to illustrate the benefits and shortcomings of the schemes