Routing Issues for Leo Satellite Constellations

We present diierent issues of routing in LEO satellite constellations. The nature of the problem itself needs further explanations. The exact market of these systems lets many questions open, although some models have been advanced. The structure of the ISLs vary from one design to another and impacts signiicantly the optimization. The movement of the satellites also gives to the system a dynamism that has to be handled. Radio propagation side-eeects justify multiple-coverage policies, which eventually modiies the routing problem into more multi-casting-like routing issues. Given that environment, several criteria of study and optimization can be identiied. The delay of routing can be a very critical point in that context. Also the variation of delay (also called the jitter) is important and may impact several applications. Some more traditional aspects can be maximized, such as the throughput, and the non-interruption of the opened connections. The advantages of satellites compared to traditional terrestrial systems are clear. The satellites allow to deploy new services on very large areas, in a uniform way. Also, the traditional need for heavy in-frastructures to access the end-user is solved by simple installations of parabolic antennas or even smaller devices. Meanwhile, a satellite system needs some time to be designed and launched. Even if the satellites themselves are scheduled for launch in a short period, the complete study of the system is usually not completed in less than a couple of years. The dynamism of modern telecommunication markets is such that the nal usage of the system is not known at the beginning of its conception. A clear example of that is the ICO system that was originally designed for personal communications and which nally targets the data market. Three major scenarios can be identiied for satellite markets. The rst one, and the most natural one, states that satellites will address countries where the telecommunication infrastructure is insuucient or in-existing. The second one, which appears as more and more probable, is that the satellites will provide additional capacities to countries that already have good telecommunication infrastructures, but which suuer JJrrme Galtier is with France Telecom R&D and INRIA, from overload of the resources. A third market concerns people who require a seamless connection in their international activities. Of course, depending on the scenario, the traac may have diierent characteristics , summarized in Table I. Little is known on the two rst classes of applications. The last one …