Implications of a Selective Acknowledgment Scheme on Satellite Performance

Data link response time is becoming more of a concern today with the onset of satellite transmissions of computer data. The long propagation delay inherent to satellite communications may lead to a degradation in data link response time as compared to the same transmission over purely terrestrial links. Furthermore, data link errors need be considered in any such study of response time of satellite data links. A model has been developed to study data link response time under a selective acknowledgment retransmission protocol. The model not only calculates mean link response time, but also the second moment of the response time. This model is then applied to various interactive data transmission schemes over a half-duplex (HDX) satellite link with terrestrial tails, although modifications can easily be made to analyze pure terrestrial or satellite links. The model parameters include bit error rate (BER), terrestrial as well as satellite propagation delay, modem transit delay, MAXOUT (maximum number of unacknowledged data frames), frame size (bits), and message size (bits).