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Technical support for digital systems technology development. Task order 1: ISP contention analysis and controlAlternatives for realizing a packet-based network switch for use on a frequency division multiple access/time division multiplexed (FDMA/TDM) geostationary communication satellite were investigated. Each of the eight downlink beams supports eight directed dwells. The design needed to accommodate multicast packets with very low probability of loss due to contention. Three switch architectures were designed and analyzed. An output-queued, shared bus system yielded a functionally simple system, utilizing a first-in, first-out (FIFO) memory per downlink dwell, but at the expense of a large total memory requirement. A shared memory architecture offered the most efficiency in memory requirements, requiring about half the memory of the shared bus design. The processing requirement for the shared-memory system adds system complexity that may offset the benefits of the smaller memory. An alternative design using a shared memory buffer per downlink beam decreases circuit complexity through a distributed design, and requires at most 1000 packets of memory more than the completely shared memory design. Modifications to the basic packet switch designs were proposed to accommodate circuit-switched traffic, which must be served on a periodic basis with minimal delay. Methods for dynamically controlling the downlink dwell lengths were developed and analyzed. These methods adapt quickly to changing traffic demands, and do not add significant complexity or cost to the satellite and ground station designs. Methods for reducing the memory requirement by not requiring the satellite to store full packets were also proposed and analyzed. In addition, optimal packet and dwell lengths were computed as functions of memory size for the three switch architectures.
Document ID
19940008336
Acquisition Source
Legacy CDMS
Document Type
Contractor Report (CR)
Authors
Stehle, Roy H. (SRI International Corp. Menlo Park, CA, United States)
Ogier, Richard G. (SRI International Corp. Menlo Park, CA, United States)
Date Acquired
September 6, 2013
Publication Date
January 1, 1993
Subject Category
Space Communications, Spacecraft Communications, Command And Tracking
Report/Patent Number
E-7564
NAS 1.26:190758
NASA-CR-190758
Accession Number
94N12809
Funding Number(s)
CONTRACT_GRANT: NAS3-25934
PROJECT: RTOP 690-60-21
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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