Performance of a hybrid terrestrial/satellite ATM network-experimental results for CBR traffic CTD and CDV QOS parameters

Through a comprehensive empirical study, the characteristics of CDV (jitter) and CTD of a hybrid terrestrial/satellite ATM network transporting CBR traffic were determined. In particular, the impact of a commercial, digital satellite modem on the two QoS parameters was examined. We found that the digital satellite link does not affect the end-to-end jitter regardless of the type of error correction or buffer size used by the satellite modem. However, the mean of the CTD is affected by the choice of error correction technique and the buffer depth in the modem. We also captured data showing that the auto-correlation function measuring the dependency between events (cells) is affected by the use of the satellite link. Analysis of the cells received from an ATM network with and without the satellite link showed different relationships among them for every tested modem configuration. Finally, our experiments revealed that a test signal passing through an ATM network supporting multiple speeds, has different CDV and CTD values depending on whether it was routed from high to low speed or vice versa. Although, this asymmetry is not directly related to the satellite equipment, it is of particular importance to satellite networks that may not always operate at the same speeds as the ATM networks they are connected to.