Hi!
Who are interested in RealTime services ?
Regards Lars Westberg,
Ericsson Research
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>From owner-pilc@lerc.nasa.gov Mon Dec 14 17:37:53 1998
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Date: Mon, 14 Dec 1998 11:26:09 -0500
To: pilc@lerc.nasa.gov
From: William D Ivancic <William.D.Ivancic@lerc.nasa.gov>
Subject: TCP over wireless type links
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Relative to discussion at the PILC BOF, I strongly support generation of a
document that indicates the basic link requirements that current TCP
implementations expect so that link designers can properly engineer the
links (when possible). It would also be useful to document general
characteristics of various communication links - particularly satellite and
wireless links so that transport protocol implementers understand some of
the problems that the link layer designers have. Information that
addresses the difficulties in meeting all current TCP link layer
requirements would be useful.
During the IETF performance implications of link characteristics BOF, some
insightful comments were made regarding TCP's control algorithms and the
changing characteristics of the Internet. Many unique networks were
presented some with various common elements. To paraphrase the statement,
control systems can be well design for a bounded problem with bounded
parameters. When those parameters are exceeded, the system may become
unstable. Current TCP works fairly well for much of today's Internet, but
does exhibit shortcomings in certain situations such as low-data-rate
low-RF-bandwidth wireless communications.
For moderate and high-data-rate links (greater than 10s of kbps),
techniques to provide data links that meet the requirement of current TCP
are fairly well understood and reasonable doable (i.e. concatenated
convolutional and Reed-Solomon coding, interleaving, correction for
erasures, etc…) In additions, some minor modifications may help improve
overall performance. However, these techniques cannot be practically
applied to low-data-rate low-RF-bandwidth (10s of kbps and less).
Furthermore, some of these links experience short outages and fades. Thus,
it is highly probable that such links will require a different transport
protocol or major modifications to current TCP in order to perform
efficiently (both in usable data throughput and RF bandwidth utilization).
Therefore, I suggest that we consider separating the low-data-rate
low-RF-bandwidth wireless problems for those of moderate and high-data-rate
communication links (wireless or otherwise).
*********************************************
William D. Ivancic
NASA Lewis Research Center
21000 Brookpark Rd. MS 54-8
Cleveland, Ohio 44135
USA
Phone: 1 216 433 3494
FAX: 1 216 433 8705
Email: William.D.Ivancic@lerc.nasa.gov
wivancic@lerc.nasa.gov
*********************************************
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