Aggregation of bitmapped feedback for improved reliable multicast scalability

A number of methods have been suggested for reducing the risk of feedback implosion in reliable multicast. In tandem with the use of negative acknowledgements (NAKs), one of the most effective of these is the router-assist function of feedback aggregation. Feedback aggregation has hitherto only applied to conventional per-packet NAKs; however, it would be far more efficient if used in conjunction with bitmapped feedback. Hence in this paper, we describe a scheme for aggregation of bitmapped NAK feedback packets, and we show its simplicity, practicality and interoperability with basic router functions. We present some useful analysis of the scheme, which might also apply to NAK aggregation in general under certain circumstances. Finally, we perform simulations showing the benefits of the scheme to uplink traffic load.