Objective
The main objectives of the Action are to study, define, implement and test systems for Local Area Network (LAN) interconnection through non-geostationary satellites.
Nowadays, LANs can be found in most offices, Universities, industrial sites, etc. These networks are capable of supporting data rates of several thousands of kbit/s. The explosion in demand for network services and applications, predominantly via the Internet, together with the increasing internationalisation of work practices, have highlighted the necessity to implement global networks capable of providing high data rate broadband multimedia type services (e.g. video, still images, data).
Nevertheless, the wide-spread establishment of long distance terrestrial networks at data rates comparable with those of LANs is still a long way off. Terrestrial integrated broadband networks are gradually being deployed throughout the world. However, owing to the high investment costs, the installation of these optic fibre networks will be a long-term operation and will never attain 100% coverage, by reason, for example, of geographic constraints. It is anticipated that the future digital broadband network will consist of both terrestrial and space components.
Satellites will play an important role in the deployment of the future broadband digital network. For example, the instantaneous continental service coverage area offered by a satellite will enable broadband networks to be deployed at a much faster rate than that of its terrestrial counterpart. Furthermore, areas or regions will be covered with equal priority, irrespective of economic, demographic or geographic constraints.
The use of satellites for the provision of services will apply particularly to remote and less developed regions, where access by terrestrial fibre is not commercially attractive, on account of high installation costs. In such areas, economic and social integration with the wider community is a major priority. Earlier opportunities for the implementation of multimedia services will be made available by using satellites.
The satellite configuration in an integrated environment has considerable scope for variation. Essentially, four types of satellite orbit can provide the space element in an integrated space/terrestrial network, namely : geostationary orbit (GEO) ; highly elliptical orbit (HEO) ; medium earth orbit (MEO), and ; low earth orbit (LEO).
Currently, satellite communications in Europe are provided by GEO satellites, however, in recent years, a number of non-geostationary LEO and MEO satellite systems have been proposed for the provision of mobile and fixed communication services.
LEO satellites orbit the earth at altitudes of in the region of 500-2,000 km. To be able to provide a continuous global communication service, it is necessary to place a number of satellites in orbit, equally spaced around the earth in a number of orbital planes. These satellites can be placed in either an inclined or polar orbit, or a combination of the two. Examples of LEO systems include Iridium (66 satellite configuration) and Globalstar (48 satellite configuration). MEO satellites are deployed in inclined circular orbits at altitudes of about 10,000 km. The MEO satellite solution offers a compromise between the LEO and GEO solutions. Between ten and twenty satellites are required to provide global coverage ; each satellite is visible from the ground for roughly one hour during its six hour orbital period. This limits the number of handovers required by the network. From a user's perspective, standard applications should be supported across all types of network and hence, the requirement to transport standard network protocols across both space and terrestrial components will be required. Ideally, the user should be unaware of the type of network used to provide the required service or application, be it terrestrial or satellite. The phenomenal success in recent years of the Internet has resulted in the TCP/IP protocol being the most widely used network protocol. TCP/IP has been developed for terrestrial network applications, which are characterised by low transmission delay and bit error rates. In an integrated space/terrestrial network, the ability to transmit the TCP/IP protocol, or its future derivatives, over the space segment will be required. Of the candidate orbits, the geostationary orbit introduces a significant delay in transmissions - just over a quarter of a second for a single earth-to-space round trip. However, MEO systems, with transmission delays ranging from 50-100 ms, are very close to the delay performance in typical LANs (40-70 ms) and appear to offer a promising solution. Nevertheless, there are several challenges that need to be overcome before MEOs can provide transparent LAN-to-LAN interconnection. These challenges will be addressed as part of the Action.
Current status
Only one meeting has occurred. Further work is planned to begin immediately the annual grant is notified.
Work planned
An invited paper describing the aims and objectives of the COST 253 action will be presented at the two-day IEE Colloquium 'EU's Initiatives in Satellite Communications', to be held at the IEE Savoy Place, London (UK),
8/9 May 1997.
Another invited paper describing the aims and objectives of the COST 253 action will be presented at the COST 254 workshop planned for Toulouse (F), in July 1997.
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31028 Toulouse
France