Delay bound and packet scale rate guarantee for some expedited forwarding networks

Abstract

Expedited Forwarding (EF) is a service defined under the Differentiated Services framework. Based on its recently revised definition in IETF RFC 3246, Packet Scale Rate Guarantee (PSRG) is its key construct, with which bounded nodal delay and edge-to-edge delay are provided. In this paper, we study the delay bound and PSRG for some EF networks. In these networks, each server belongs to a wide scheduler family which captures how much the server can be either late or earlier with respect to its reference fluid server. We show that edge-to-edge delay bound can be improved for EF networks of such servers. We also prove that PSRG can be derived from delay bound and call this PSRG-from-delay-bound property. With this property, we derive and discuss edge-to-edge PSRG for both a per-flow scheduling network and an aggregate scheduling network. In the derived results, delay bound and PSRG are a function of burstiness parameters of flows at the ingress edge. We hence further argue with analytical support that smoothing traffic at ingress edge can improve edge-to-edge delay bound and PSRG for the considered EF networks.