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InGaAsP has proved far from easy, but suitable devices are now available and undergoing life tests. Other planned cables discussion. Short systems of up to 150 km offer in- teresting possibilities, for developments in optical technology means that spans of this length can now be contemplated without having to use in- termediate repeaters, giv- ing a useful saving in cost. Such systems will offer an attractive option on routes which are too long for satisfactory performance from microwave radio links. Cable or satellite Arguments of the relative merits of satellites and cables are very complex. Each case must be treated on its own merits bearing in mind techni- cal, economic and• political factors. Never- theless, there are a few broad principles that may help in understanding some of the factors influ- encing decisions about which to use. First, satellite and cable links both continue to get cheaper as each new generation offers lower cost per circuit. Second, a signal crosses t...