Selective-Repeat Protocol with Multiple Retransmit Timers and Individual Acknowledgments

A new variant of the selective-repeat protocol is presented. While the protocols used until now have been based on cumulative acknowledgments and a single retransmit timer, a protocol based on individual acknowledgments and a separate timer for each outstanding packet is proposed here. In spite of a slightly increased complexity of the proposed protocol, when comparing it to the basic selective-repeat protocol, it is still relatively simple to be implemented; furthermore, it seems to be even less complex than the selective-reject protocol. The simulation results presented in the paper show that the new protocol is more efficient not only than the basic selective-repeat protocol, but also than the selective-reject protocol. Because the basic protocol is especially nonefficient when several packets in line are lost, the advantage of the proposed protocol is especially distinctive in case of heavy losses in the channel, but also in case of long channel delays. The relative efficiency of the proposed protocol is almost the same as the relative efficiencies of the basic and selective-reject protocols. Therefore, the new protocol seems to be most suitable in nonmultiplexing environments, especially in the datalink layer where cumulative acknowledgment single timer go-back-N protocols have mostly been used until now.