In this chapter we have looked at network service models and discovered that this is a complex area where there is a lot of debate on how to provide what is perceived as the need for guarantees for multimedia networked applications.
The very idea of guarantee is suspect to an engineer. In fact, what a network offers are services which provide probabilities of meeting some performance requirements. The performance bounds may involve more or less refined, individual offerings (i.e. to pairs or groups of users) or overall performance metrics to the set of typical users, or something in between. The contract concerning performance statistics may be made sometime in advance through subscription, or immediately before (or even remade during) each session. The costs of the various technical approaches to providing different performance bounds are not fully understood yet.
This area is extremely active in terms of research, standards development, and technology deployment. However, a very important aspect of it is the effect of pricing, which is outside the scope of this chapter or book. It is important to realize though, that the best technical solutions are often swept away by marketing!