China Academy of Space Technology is making its first attempt to develop a geostationary, broadband multimedia multi-beam communication satellite to serve mainland China and regions around. One important feature of this satellite is that it is totally different from the traditional 'bent pipe' transponder, it is an on-board regenerative, on-board switching satellite. The core element that supports on-board switching is the on-board ATM switch. There are two reasons for using ATM transport and switching in the satellite. First, ATM transport and switching is supported by the backbone network of B-ISDN, thus satellite ATM allows more compatibility. Second, the switching function is implemented by hardware and very fast, whereas in routers, routing is largely implemented by software and slow. In the long latency satellite link, ATM switch is superior to routers. This paper outlines some general considerations about how to design an on-board satellite ATM switch. First it should be made clear what kind of switch is needed. The design objective is to develop a simple, reliable switch that meets the delay, error rate, and space constraints. With this design objective in mind, hardware structure of the ATM switch is discussed. The switch is made up of the following blocks: input/output processing modules, switching fabrics, internal buffers, signaling modules and network management modules. For every block there are many kinds of different configurations, which lead to different performances. The paper reviews the different configurations of these blocks and chooses the optimum configuration. In the eyes of a computer system engineer, the ATM switch is a special purpose computer. It executes a special task and has special performance equirements. General purpose operating system will not be suitable for the switch, and a special purpose, embedded real-time operating system should be developed. This operating system manages the mission-specific low layer functions of memory, processes and devices. Upper layer functions are built on this operating system. This paper analyses the software functions and the operating system rchitecture of the switch and proposes the way to construct the operating system. Designing a satellite ATM switch is a big project. Finally, the paper makes some remarks on conclusions and future works.
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