ause disruptions. Most large users of VSAT networks have some leased lines available to use as backup when disruptions occur. Potentially high startup costs for small installations-A small company may face a high startup cost if it does not have many nodes. (If VSAT is the only available recourse-if there is no way to communicate without it- then the installation cost is a moot point.) MEO Satellites MEO satellites orbit at an elevation of about 6,200 to 9,400 miles (10,000 to 15,000 km). MEO satellites are closer to the earth than GEO satellites, so they move across the sky much more rapidly-in about one to two hours. As a result, to get global coverage, you need more satellites (about five times more) than with GEO systems. But because the altitude is lower, the delay is also reduced, SO instead of a 0.5-second delay, you see a 0.1-second delay. The main applications for MEOs are in regional networks, to support mobile voice and low-speed data, in the range of 9.6Kbps to 38Kbps. The companies that use MEOs tend to have their movement within a region rather than over the entire globe, SO they want a larger footprint over, for example, the Asia-Pacific region, to support mobility of mainly voice communications. Unusable Satellite Orbiting Altitudes The orbiting altitudes between about 1,000 miles and 6,200 miles (about 1,600 km and 10,000 kr cannot be used for satellites because the Van Allen radiation belts act nega- tively on satellites. The Van Allen belts are an area of charged particles (resulting from cos- mic rays) above the earth trapped by the earth's magnetic field. LEO Satellites LEOs are a lot like cellular networks, except that in the case of LEOs, the cells as well as the users are moving. Because LEOs are in such low orbits, they greatly Chapter 2 Traditional Transmission Media reduce the transit times, SO the delays are comparable to what you'd experience on the PSTN, and therefore delay-sensitive applications can survive. Their low orbits also mean that power consumption is much lower than with a