Worst-case analysis for deterministic allocation in a differentiated services network

The differentiated service architecture is proposed as a scalable approach to QoS for IP networks. Therefore it is based on the aggregate (per class) scheduling of packets, but it aims at providing QoS to single flows. In particular the expedited forwarding (EF) per hop behavior (PHB) and the related premium service have been defined in order to provide determinist QoS guarantees to IP flows: zero loss and very low delay and jitter. Hence a possible approach to characterize and to dimension a network using the EF PHB is the worst-case analysis. We propose a worst case analysis which provides bounds to the queuing delay for a class of network topologies. Our results are compared with similar available results, which provide "looser" bounds. The comparison with simulation results shows that the bound is not enough tight to be of practical use. We justify the reason for this behavior and indicate directions for further improvements.