Modelling asynchronous transfer mode (ATM) traffic over the satellite bearer

The analysis and modelling of ATM over the satellite bearer aid the system designer by providing bounds for the selection of equipment and parameter settings. In this way, efficient use can be made of the limited bandwidth available to the military user. Errors originating on the physical medium cause data to be lost and impact on data throughput efficiency. In order to evaluate this effect, models have been developed that relate the data packet size, bit error ratio (BER) and link bit-rate. Results from these models indicate the optimum choice of packet size to maximise data throughput efficiency. Critical services, with stringent time and delivery constraints, are likely to require reserved virtual channels in the ATM "pipe". The remaining bandwidth can be used for other services that do not require such tight service guarantees. The available bit rate (ABR) service category is of particular interest for this purpose. Using ABR, sources may send data up to an agreed peak ATM cell rate, but in the event of congestion, inherent feedback mechanisms reduce the source cell rate down to an agreed minimum. Simulations carried out using the OPNET modelling tool indicate that ABR traffic can exhibit unusual or poor performance when carried over a data link that includes a long-delay satellite segment. Moreover, other ABR traffic that shares the data link can also be affected, even if it does not use the satellite portion of the link. The application of virtual source/virtual destination (VS/VD) behaviour to divide the link into separately-controlled individual segments could circumvent these problems.