NAK-based Flow Control Scheme for Reliable Multicast Communications

In reliable multicast communications, lost information due to packet loss should be re-multicasted. NAK-based retransmission scheme is said to be effective for scalable reliable multicast communications because it can avoid implosion of control packet. When the source sends packets faster than receiver’s capacity, packet loss due to buffer overflow occurs constantly at corresponding receivers. With this constant packet loss, implosion of control packet degrades total throughput seriously even in the case of NAK-based retransmission scheme. In order to prevent this kind of constant packet loss at receivers, flow control scheme should be implemented for reliable multicast communications. In the paper, we propose a new flow control scheme, which is suitable for NAK-based retransmission scheme. From the viewpoint of flow control, receiving a NAK intends that 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, rate may be decreased excessively. In the paper, log information of 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.