This paper presents an admission control framework for Expedited Forwarding (EF) traf®c in a Differentiated Service Network. The aim is to overcome the limitations, in terms of achievable ef®ciency, which are proper of a deterministic ªworst-caseº approach based on the zeroloss assumption. An admission control procedure is de®ned which provides quanti®able end-to-end QoS guarantees in terms of maximum delay and per-¯ow loss probability. The admission control scheme relies on the analytical derivation of a bound for the per-¯ow loss probability at a generic network node. The analytical approach is based on the insertion of a discarding device before the EF queue. The purpose of the dropper is to discard packets in order to avoid con¯icts at burst scale in the queue, and allows for simple analytical handling of the per-¯ow loss process. The degradation of the statistical characteristics of the ¯ow along its path are taken into account.
Finally, a comparison between analytical bounds and actual performance results obtained by simulations is presented. The results show that the requested QoS targets are largely met and that the achievable ef®ciency is much higher than that derived from the worst-case allocation.