Simple Performance Models of Di erentiated Services Schemes for theInternet

Schemes based on the tagging of packets have recently been proposed as a low-cost way to augment the single class best eeort 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 beneets and drawbacks of the diierent tagging schemes and of the mechanisms in each scheme (for example how much RIO contributes in the Assured scheme), and to tackle key performance and economic issues (e.g. the diierence in tarii between diierent service classes would presumably depend on the diierence in performance between the classes). Our goal in this paper is to obtain a quantitative description of the service provided by tagging schemes. Speciically, we describe and solve simple analytic models of two recently 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 beneets and shortcomings of the schemes.