On cycle based schedulers with time alternating priorities

Abstract

The paper discusses new scheduling algorithms that are modifications of classical cycle based scheme, named the cycle based algorithm with time alternating priorities and time guard. The classical cycle based algorithm assumes that a given packet stream can be served only in predefined periods while it is not entitled to receive service in the periods dedicated to serve other packet streams. This property leads to non-work conserving behavior of the system and, as a consequence, rather poor packet transfer characteristics (expressed by packet delay and packet loss ratio in the case of system with a finite buffer). On the other hand, the important advantage of this algorithm is that it guarantees performance isolation among different packet streams. The proposed modification assumes that in the periods dedicated for service of a given packet stream the scheduler can also serve the packets belonging to other streams but with assigned lower priorities. In this way we transform the behavior of the cycle based algorithm to the form of nearly work conserving. In the paper we provide exemplary simulation results showing the effectiveness of the proposed algorithms in terms of packet delay characteristics and guarantees about performance isolation. Finally, we show the application of the studied scheme to the IIP System with virtualized network infrastructure requiring isolation among virtual links sharing a given link capacity.