This paper presents a performance evaluation of NAK-based reliable multicast communication protocols operating in an environment where end-to-end delay are heterogeneous. In the case of heterogeneous delay, performance of a timer-based retransmission control scheme may become worse. We show that a counter-based retransmission control scheme works well in the case of heterogeneous transmission delay. We also compare two NAK-based protocols and show that a NAK-multicasting protocol outperforms a NAK-unicasting protocol from the viewpoint of scalability even when delays are heterogeneous.

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 packets. When the source sends packets faster than receiver's ability, packet loss due to buffer overflow occurs constantly at corresponding receivers. With this constant packet loss, implosion of control packets 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 suitable for NAK-based retransmission scheme. From the viewpoint of flow control, receiving a NAK indicates that transmission rate is too high. However, in multicast communications, multiple NAKs may be generated for a corresponding packet. If the transmission rate is decreased simly by receiving a NAK, the rate may be decreased excessively. In the paper, logging information of transmission rate stored at the sender is proposed to be effective to prevent the transmission rate. Performance evaluation by computer simulation shows that the proposed scheme notably improves throughput performance compared with the case of no flow control.

This paper evaluates the performance of a reliable multicast protocol for bulk-data transfer over unreliable networks via IP-multicast. Bulk-data type reliable multicast appears promising for commercial publishing and large-scale data replication. The proposed reliable multicast transport protocol (RMTP) provides high-performance due to the use of IP multicast while also providing confirmed and error free transfer by end-to-end controls. The protocol includes a multi-round selective repeat scheme dedicated for bulk-data multicast applications. This paper examines the multicast retransmission procedures in RMTP through analysis and tests on an implemented system and clarifies the basic performance behavior of the protocol. Evaluations are conducted with regard to retransmission redundancy, transfer time, and packet processing load with various error conditions and number of receivers. Against the response concentration problem seen in end-to-end communication, the backoff time algorithm is applied to the protocol; the limits it places on system scalability are clarified.