Although in recent years, considerable efforts have been exerted on treating the congestion control problems of ABR services in the ATM networks, the focus has been so far mostly on unicast applications. The inclusion of the emerging multicast services in the design of congestion control schemes is still at its infancy. The generic rate-based closed-loop congestion control scheme proposed by the ATM Forum for ABR services suffers from large delay-bandwidth product. VS/VD behavior is therefore proposed by the Forum as an supplement. In this paper, two VS/VD behavior congestion control schemes for multicast ABR services in the ATM networks are examined : forward explicit congestion notification (FECN) and backward explicit congestion notification (BECN). Their performances are analyzed and compared. We further observe that both VS/VD schemes alleviate the problem of consolidation noise and consolidation delay of the RM cells returning from the downstream nodes. The alleviation of consolidation noise and consolidation delay is a major concern of most present researches. Simulation results are also given to support the validity of our analysis and claims.

Recently we have studied the performance of the VS/VD behavior for two binary feedback congestion control schemes, FECN and BECN, when they are applied to multicast ABR services. It is shown that the VS/VD schemes alleviate the problems of consolidation noise and consolidation delay, which are two major design issues in multicast congestion control. To complement, we further explore the VS/VD behavior for the explicit rate feedback control scheme in this letter. Through an efficient rate estimation method, it is again observed that VS/VD behavior performs better than the traditional end-to-end schemes.