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Control Mechanisms
Full Paper
Decoupling QoS Control from Core Routers: A Novel Bandwidth Broker Architecture for Scalable Support of Guaranteed Services
Zhi-Li Zhang (University of Minnesota)
Zhenhai Duan (University of Minnesota)
Lixin Gao (Smith College)
Yiwei Thomas Hou (Fujitsu Labs)
We present a novel bandwidth broker architecture for scalable support of guaranteed services that decouples the QoS control plane from the packet forwarding plane. More specifically, under this architecture, {\em core routers do not maintain any QoS reservation states, whether per-flow or aggregate}. Instead, the QoS reservation states are stored at and managed by a bandwidth broker. There are several advantages of such a bandwidth broker architecture. Among others, it avoids the problem of inconsistent QoS states faced by the conventional hop-by-hop, distributed admission control approach. Furthermore, it allows us to design efficient admission control algorithms without incurring any overhead at core routers. The proposed bandwidth broker architecture is designed based on a {\em core stateless} virtual time reference system we developed earlier. This virtual time reference system provides a unifying framework to characterize, in terms of their abilities to support delay guarantees, both the {\em per-hop behaviors} of core routers and the {\em end-to-end properties} of their concatenation. In this paper we focus on the design of efficient admission control algorithms under the proposed bandwidth broker architecture. We consider both {\em per-flow} end-to-end guaranteed delay services and {\em class-based} guaranteed delay services with flow aggregation. Using our bandwidth broker architecture, we demonstrate how admission control can be done on an entire {\em path} basis, instead of on a ``hop-by-hop'' basis. Such an approach may significantly reduce the complexity of the admission control algorithms. In designing class-based admission control algorithms, we investigate the problem of flow aggregation in providing guaranteed delay services, and devise a new apparatus to effectively circumvent this problem. We conduct extensive analysis to provide theoretical underpinning for our schemes as well as to establish their correctness. Simulations are also performed to demonstrate the efficacy of our schemes.