Design Choices for Selective-Repeat Retransmission Protocols

The design of selective-repeat retransmission protocols to provide reliable transfer of large data files is discussed. The transmission system is assumed capable of losing, distorting, or reordering the transmitted data frames and acknowledgment frames. The principle design considerations center on methods for managing the finite sequence number space and methods for managing the finite-sized receiver buffer. Under the assumption that there exists a maximum time from transmission of a frame to receipt of an acknowledgment for that frame, methods are described for safe reuse of frame sequence numbers. Previous results by Metzner and Morgan on buffer overflow control are extended to cover non-FIFO transmission systems. A two-dimensional space of design parameters is explored by way of Monte Carlo simulations. For appropriate designs, it is shown that significant increases in throughput over that achieved by the Go-Back- protocol are possible on high-rate long-delay channels.