Performance modeling and simulation of inquiry-response computer applications using VSATs

The authors present a model to characterize the performance of transaction-oriented applications over a communications satellite channel or an integrated terrestrial-satellite network using very small aperture terminals (VSATs) operating through a centralized hub earth station. The terrestrial access takes place through the polling technique using a bit-oriented data-link protocol. The satellite access may be either contention-based such as slotted ALOHA, or dedicated such as SCPC (single channel per carrier) or TDMA (time division multiple access) in the VSAT-hub direction and TDM (time division multiplexing) in the hub-VSAT direction. Simulation results are reported for a number of cases of practical interest. The results are applicable to the SDLC/SNA (synchronous data link control/System Network Architecture) environment and closely approximate the HDLC (high-level data link control) or X.25 protocol environment. Further, the impact of various system parameters on the network response time is evaluated. It is shown that, through protocol spoofing, a number of cluster controllers connected to a VSAT through multidrop lines at the speed of 9.6 kb/s or higher can communicate to a front-end processor connected through 56 kb/s or higher terrestrial links to a hub station. A network response time of less than 2 s can be achieved if speed on multidrop lines from the cluster controller unit to the VSAT is larger than 19.2 kb/s