Next articleAn important element of satellite-supported asynchronous transfer mode (ATM) networking will involve support for the routing and rerouting of active connections. Work published under the auspices of the Telecommunications Industry Association (http://www.tiaonline.org), describes basic architectures and routing protocol issues for satellite ATM (SATATM) networks (ref. 1). The architectures and issues identified will serve as a basis for further development of technical specifications for these SATATM networks.
Three ATM network architectures for bent pipe satellites and three ATM network architectures for satellites with onboard ATM switches were developed. The architectures differ from one another in terms of required level of mobility, supported data rates, supported terrestrial interfaces, and onboard processing and switching requirements. The documentation (ref. 1) addresses low-, middle-, and geosynchronous-Earth-orbit satellite configurations.
The satellite environment may require real-time routing to support the mobility of end devices and nodes of the ATM network itself. This requires the network to be able to reroute active circuits in real time. In addition to supporting mobility, rerouting can also be used to (1) optimize network routing, (2) respond to changing quality-of-service requirements, and (3) provide a fault tolerance mechanism. Reference 1 examines the various reroute events and the time-scale in which they would occur.
Traffic management and control functions are necessary in ATM to ensure that the quality-of-service requirements associated with each connection are not violated and also to provide flow and congestion control functions. Functions related to traffic management were identified and described. Most of these traffic management functions will be supported by on-ground ATM switches, but in a hybrid terrestrial-satellite ATM network, some of the traffic management functions may have to be supported by the onboard satellite ATM switch. It is expected that the ATM traffic loading on the satellite will be high; hence, it has been proposed to transfer traffic management functions (to the degree possible) to Earth station components. This will also reduce the complexity of the satellite hardware. Future work is planned to examine the tradeoffs of placing traffic management functions onboard a satellite as opposed to implementing those functions at the Earth station components. This work was done at the NASA Lewis Research Center in collaboration with ComSat Labs.
Find out more about the research of the Communications Division.
Lewis contact: Thomas C. vonDeak, (216) 433-3277, fax
(216) 433-8705,
Thomas.C.Vondeak@grc.nasa.gov
Authors: Thomas C. vonDeak and Ferit Yegendu
Headquarters program office: OSS
Programs/Projects: ATM research and development,
SOMO, satellite communications industry
Last updated June 16, 1999, by Nancy.L.Obryan@nasa.gov
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