SDLC PROTOCOL THROUGHPUT ANALYSIS.

Abstract

A mathematical model is presented to determine large message throughput in local or long-haul networks utilizing the synchronous data link control (SDLC) protocol. The model includes provisions for wait time which includes processor service times, plus satellite and/or land-based propagation delays. Other inputs include the probability of ADK/NAK timeout, block size, and assumed bit error rate. Basic feedback theory is applied to both clarify and simplify the analysis. A detailed example illustrates use of the model in a communication satellite application to illustrate large message throughput degradation caused by the satellite propagation delay for various bit error rates. An empirically derived simple expression to determine optimum block size for maximum throughput as a function of bit error rate is presented.