RACOOM: A Rate-Based Congestion Control Scheme for Multicasts

As continuous media multicast applications become widely deployed on the Internet, it becomes increasingly important to ensure these applications respond to network congestion in a TCPfriendly manner so as to coexist with TCP flows (which constitutes the majority of the Internet traffic). In this paper, we present a RAte-based COngestion cOntrol scheme for Multicasts, called RACOOM. In the absence of packet loss, a RACOOM session keeps track of the congestion status of the on-tree path with the largest RTT, and adjusts its sending rate using a TCP Vegas-like method. Upon packet loss (anywhere in the multicast tree), RACOOM then responds by reducing its sending rate by half in a TCP Reno-like manner. The acknowledgement aggregation method used in RACOOM is judiciously designed to prevent ACK explosion and yet provide the sender with a simple but comprehensive view of congestion conditions in the multicast tree. Through analysis using control theory and simulation study in ns-2, we show..