The prospect of the Internet as the fastest growing satellite communication application coupled with satellite-based multimedia networks has generated a high level of interest in the performance of TCP over satellite systems. This article presents the network architecture for supporting TCP/IP based services over satellite. It discusses the key factors that influence TCP performance over satellite links, and compares the advantages and disadvantages of low earth orbit and geostationary satellites. The article also discusses the feasibility of using Low Earth Orbit satellites to support and expand the Internet. It presents studies of the TCP behavior over a Geostationary satellite system and LEO satellite constellation based on computer simulations, where two typical Internet applications are taken into consideration: FTP file transfer and Web browsing.
With its ability to caver large area including geographically isolated regions, the satellite based links have a bright future.. A number of commercial satellite systems have been proposed which target multimedia services, as illustrated in Table 1 . These systems are based on both geostationary earth orbit (GEO) and low earth orbit (LEO) satellite networks.
With a shortage of broadband terrestrial connections in many areas of the world, particularly in remote or rural areas where physical lines are costly to install and operate, satellites can be used to complement terrestrial networks, extending them with flexible and immediate wide coverage.
Low earth orbit(LEO) and Geostationary orbit satellites (GEO) are used to provide the satellite links.
LEO satellite constellations
Having lower altitude, LEO satellites can be used
to provide a satellite network with much lower time delays
and propagation losses. It is also possible to achieve truly
global coverage with a network based on LEO satellites with
The use of LEO satellite constellations enables designers
to minimize power in both satellites and user terminals, mini-
mize satellite antenna size, minimize the
time delay or latency for a two-way signal,
and maximize the angle of elevation.
disadvantages of LEO
The orbital period is very short (around 100 minutes), and a given satellite is in view for only a few minutes before hand-off of a call to another satellite.
Coverage area and no of satellites
In order to provide continuous and global coverage, a large number of satellites are required as th ecoverage area for a single satellite is very less compared to GEO. Examples of such LEO constellations are Teledesic and Iridium with 288 and 66 operational satellites, respectively. The satellites have to be maintained in constant position in the constellation for providing constant connectivity which is a major challenge.
When one satellite moves out of sigth, another has to be switched to to provide services. Handoff techniques are provided for this purpose.
Intersatellite links (ISLs) are often implemented within LEO constellation. These ISLs allow users from different satellite footprints to communicate with each other. They also allow the system to provide large geo-graphical coverage without having to deploy large numbers of gateway stations.
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