NAK-based flow control scheme for reliable multicast communications

In reliable multicast communications, lost information due to packet loss should be re-multicast. The NAK-based retransmission scheme is said to be effective for scalable reliable multicast communications because it can avoid implosion of the control packet. When the source sends packets faster than the receiver's capacity, packet loss due to buffer overflow occurs constantly at the corresponding receivers. With this constant packet loss, implosion of the control packet degrades the total throughput seriously even in the case of the NAK-based retransmission scheme. In order to prevent this kind of constant packet loss at the receivers, the flow control scheme should be implemented for reliable multicast communications. In the paper we propose a new flow control scheme, which is suitable for the NAK-based retransmission scheme. From the viewpoint of flow control, receiving a NAK intends that the transmission rate is too high. However in multicast communications, multiple NAKs may be generated for a corresponding packet. If simply receiving a NAK decreases the transmission rate, the rate may be decreased excessively. In the paper, log information of the transmission rate stored at the sender is proposed in order to prevent the transmission rate from decreasing excessively. Performance evaluation by computer simulation shows that our proposed scheme notably improves throughput performance compared with the case of no flow control.