An efficient packet service algorithm for high-speed ATM switches

Abstract

The unprecedent development of the World Wide Web, and the emerging of new types of applications such as video-on-demand and teleconferencing put an increasing pressure on the communication infrastructure. One of the main components that directly determine the communication bandwidth and the quality of services that are provided are the communication switches. In this paper, we propose a new scheduling algorithm for servicing the output sessions of a high-speed ATM switch that is both accurate and efficient. To each session we associate a weight w that represents the share of the communication bandwidth it should receive. To characterize the allocation accuracy we give bounds for the difference (called lag) between the number of time slots that each session should receive and the number of time slots it actually receives. Specifically, we show that in the particular case in which the aggregate weight W over all sessions is a power of two, the lag of a session with weight w is bounded by O( ones( w)), where ones( w) represents the number of ones in the binary representation of w. In the general case in which the aggregate weight has an arbitrary value, we show that the session's lag is bounded by O(log w). The selection of the session to be serviced during the next time slot takes O(log log W). We also propose a simple hardware implementation that reduces the selection time complexity to O(1). Finally, we discuss the application of our algorithm in the context of both work-conserving and non-work-conserving disciplines.