We propose and develop a novel virtual time reference system as a unifying scheduling framework to provide scalable support is designed as a conceptual framework upon which guaranteed services can be implemented in a scalable manner using the DiffServ paradigm. The key construct in the proposed virtual time reference system is the notion of packet virtual time stamps, whose computation is core stateless, i.e., no per-flow states are required for its computation. In this paper, we lay the theoretical foundation for the definition and construction of packet virtual time stamps. We describe how per-hop behavior of a core router (or rather its scheduling mechanism) can be characterized via packet virtual time stamps, and based on this characterization, establish end-to-end per-flow delay bounds. Consequently, we demonstrate that, in terms of its ability to support guaranteed services, the proposed virtual time reference system has the same expressive power and generality as the IntServ model. Furthermore, we show that the notion of packet virtual time stamps leads to the design of new core stateless scheduling algorithms, especially work-conserving ones. In addition, our framework does not exclude the use of existing scheduling algorithms such as stateful fair queuing algorithms to support guaranteed services.
Bibliographical noteFunding Information:
Manuscript received October 15, 1999; revised April 15, 2000. This work was supported in part by the National Science Foundation under the CAREER Award NCR-9734428. Any opinions, findings, and conclusions or recommendations in this paper are those of the authors and do not necessarily reflect the views of the National Science Foundation.