Improved delay bound and packet scale rate guarantee for some expedited forwarding networks

Packet scale rate guarantee (PSRG) is a service guarantee defined recently for expedited forwarding (EF) service under the differentiated services framework. In the original work of PSRG [J.C.R. Bennett et al., August 2002], two classes of schedulers are proved to be PSRG servers. In addition, it is proved that end-to-end PSRG and consequently end-to-end delay bound are provided by a network of PSRG servers implementing per-flow scheduling. Moreover, a delay bound is presented for a network of PSRG servers implementing aggregate scheduling. In this paper, we show that these results can be improved for networks of PSRG servers of these schedulers. In particular, we show that the two classes of schedulers belong to a common scheduler family. In addition, we prove that the end-to-end delay bounds can be improved for networks of such schedulers. We also prove that PSRG can be derived from the delay bound and call this PSRG-from-delay-bound property. Moreover, with this property, we derive and discuss end-to-end PSRG for both the per-flow scheduling network and the aggregate scheduling network.