A Shared Buffer Memory Switch with Multicast Function Using Generalized Two-Level Priority Control

摘要

In the future, various multicast applications are anticipated for ATM networks, and many studies have examined ATM switches having the multicast function. In a shared buffer switch, the cell loss performance is clearly improved by unicast priority control that gives send priority to the unicast cell in an address copy switch. However, if the multicast traffic increases, a reduction in the priority control effect becomes a problem. To solve this unicast priority control problem, in this paper, we propose two generalized two-level priority control schemes (deterministic-threshold scheme and adaptive-threshold scheme) that give priority to cells having the number of copies below some threshold. The deterministic-threshold scheme sets the optimum threshold when the traffic state is known, and clearly reduces the cell loss probability even when the ratio of multicast cells in the input traffic is high. The problem becomes what to set the threshold to because the optimum threshold changes depending on the traffic state in this scheme. The adaptive-threshold scheme always maintains the priority control effect by automatically changing the threshold i n response to traffic variations based on the result obtained from the deterministic-threshold scheme. We use simulations to compare the adaptive scheme to conventional schemes and demonstrate the effectiveness of the adaptive-threshold scheme.