Near-earth spacecraft are considered to be very LEO satellites. The commercial constellations to be tested range from high-density LEOs to GEOs. We have presently developed a complete baseline simulation model that uses basic algorithms for all of the test parameters. We are workingnow on developing individual test modules for each parameter, which will then be plugged onto the baseline model and evaluated for each satellitesystem. The baseline model itself will be reinforced with the Opnet ATMsuite to replace the current quasi-MAC protocol.

Following the successful implementation of basic algorithms for each of these test cases (shortest path routing, hard handoff, beacon monitoring, file transfer, deterministic packet transmission, single-priority FIFO queueing), we are currently working on replacing the MAC protocol with the ATM suite. The advantages of this approach are two-fold: first, it allows usgreater flexibility in including multiple service classes, traffic types andpriority schemes. Also it creates a well-defined network/switching layer upon which TCP/IP and UDP/IP can be evaluated.