Per-domain packet scale rate guarantee for expedited forwarding

The expedited forwarding per-hop behavior (EF PHB) was recently replaced by a new definition, called packet scale rate guarantee (PSRG), under the Differentiated Services (DiffServ) framework. This replacement raises two challenges. One is the implementation of a PSRG server. Another is the provision of per-domain PSRG. Specifically, for the former, an open issue is whether hierarchical schedulers can provide PSRG; for the latter, it is not clear whether and how per-domain PSRG can be provided in the presence of flow aggregation. Since, in DiffServ networks, flow aggregation is a natural phenomenon and hierarchical scheduling is high-likely desired, these two challenges become even more critical. To address the first challenge, we introduce a new concept called latency-rate worst-case service guarantee (LR-WSG). We prove that, if a server provides LR-WSG, it also provides PSRG. We show that many well-known schedulers support LR-WSG, which include not only one-level schedulers but also their hierarchical versions. To address the second challenge, we first prove that PSRG can be extended from per-node to per-domain if no flow aggregation is performed. The proof is notable in that it depends solely on the concept of PSRG itself. We then investigate the provision of per-domain PSRG in presence of flow aggregation. We propose to use packet scale fair aggregator (PSFA) to aggregate flows. We show that, with PSFA, per-domain PSRG can be provided in spite of flow aggregation. We finally provide a brief discuss on the viability of using PSFA in DiffServ networks and define an expedited forwarding per-domain behavior (EF PDB).