As the nation and the world continue to move into the information age, access to telecommunications services for all users becomes increasingly important. Users must be able to access information services they need from their respective locations at the specific times useful to them. In order to support this broad information accessibility, telecommunications networks must use both terrestrial and satellite systems. Satellite systems complement the terrestrial systems by providing access into areas where the terrestrial system is not effective. Examples are remote areas, where terrestrial facilities are under-developed or may not exist, and areas affected by natural or man- made disasters, where terrestrial networks may temporarily be inoperable.As bandwidth and adaptivity requirements continue to increase, due to an increase in both the number or users and the range of services, implementation of terrestrial/satellite interfaces becomes more complex and difficult. These interfaces must allow satellite systems to operate as efficiently as possible and must be transparent to users.
ITS is conducting studies on advanced satellites and on the terrestrial/satellite system interfaces. Emerging advanced satellites include on-board switching and spot beams. On-board switching allows a satellite to be used as either a link or a node in a network--or both. Spot beams allow the reuse of spectrum in each beam, thus increasing the satellite capacity and allowing a mix of low- and high-data-rate users.
One of several ongoing ITS advanced satellite studies seeks to determine how satellites can be most useful in augmenting or restoring terrestrial networks. A network simulation model has been developed to support this research. The model contains both circuit-switched and packet-switched network representations. ITS also supports a NASA Advanced Communications Technology Satellite (ACTS) satellite earth station in Boulder and is an independent ACTS experimenter. In its ACTS experiments, ITS is applying system performance measures for data communications systems to determine the baseline performance of the ACTS as a network element. Finally, ITS participates in organizations that are developing the standards and protocols to be used in the terrestrial/satellite system interfaces.
