A new selective repeat scheme-actual environment performance analysis

The authors present the extended HDLC-SREJ+REJ [high-level data link control (HDLC) with sequential retransmission (REJ) and selective retransmission (SREJ)] protocol and analyze its throughput efficiency, taking into account actual mechanisms such as checkpointing, timeout, and sequence error detection. The protocol uses an accumulative acknowledge-selective-repeat scheme whereby the efficiency is improved by processing and storing the correct frames received in a SREJ exception condition even after an error detection. The key idea of the analytical approach is the use of a semi-Markov process model and the novel concept of virtual REJ/SREJ exception condition. This concept gives an easy throughput expression and allows investigation of the effect of some simplifications normally used. The numerical results confirm that extended HDLC-SREJ+REJ is better than other accumulative acknowledgement protocols. The results show that the effect of the simplifications is significant for typical terrestrial communications parameters but can be neglected for high-speed satellite communications