Quality of service is application dependent. Voice quality may be acceptable with bit error rates of
10-6 or higher. Medical imaging may find 10-7 acceptable to use since file transfers are
not delay-sensitive and the high-level protocols will resolve any problems resulting from non-error-free
transmission. Thus, the question to be resolved is: "What link quality will the satellites need to provide
in order to be globally interoperable with terrestrial systems?"
Goals
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Determine quality of service parameters that satellites must provide to remain competitive
in the Global Information Infrastructure (GII).
-
Evaluate the effect of transmission link quality and characteristics on overall quality
of service for various links of protocols
Strategy
-
Evaluate ATM over a noisy link
-
ATM was designed for "near" error-free channels such as fiber. We need to understand the effect that various error characteristics have on ATM quality of service.
-
Evaluate digital video over satellites
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Digital video (particularly compressed video such as MPEG-2) is expected to require stringent quality of service.
-
Evaluate effect of linked protocols
-
Errors that occur in the lower link of the protocol stacks tend to get
magnified as they propagate through the upper links.
-
For example, one error in one ATM cell for AAL5 will cause numerous ATM cells to be
discarded, potentially resulting in multiple TCP/IP packets to be discarded.
Presentations
MPEG 2 over ATM over Satellite Experiments: Status of Laboratory Tests (available in
Post Script,
Acrobat, and
Power Point formats)
Publications
MPEG-2 Over Asynchronous Transfer Mode (ATM) Over Satellite Quality of Service (QoS) Experiments
: Laboratory Tests (available in Post Script and
Acrobat formats)
ATM Quality of Service at 45 Mbps Using a Satellite Emulation: Laboratory Measurements (available in
Post Script and
Acrobat formats)
ATM Quality of Service Tests for Digitized Video Over ATM Over Satellite: Laboratory Tests (available in
Post Script and
Acrobat formats)
MPEG-2 Over ATM Over Satellite Quality of Service Experiments: Laboratory Tests (available in
Post Script and
Acrobat formats)
William D. Ivancic
William.D.Ivancic@grc.nasa.gov
Telephone: (216) 433-3494
