UDP versus SCPS-TP, TCP etc.

[Keith Hogie <[e-mail]>]

All,
  
  I have been following the discussion on Satellites running IP and it
seems to have gone off heavily in the TCP direction.  I realize this is
the TCPSAT group but the question seemed to be broader than just TCP.

  What we see for missions using IP is a very heavy use of UDP and not
TCP.  TCP will always have limitations that we feel are best avoided
by using UDP.  This allows us to do things like data transfers over 
one-way links which does not work with TCP.  I have seen people 
attempting to fix TCP for all sorts of special cases for years and
still don't see much convergence.

  For an example of other UDP use see the following:

  http://www.esa.int/export/esaCP/ESALS5OED2D_index_0.html
  http://www.gcs-salzburg.at/
  http://www.gcs-salzburg.at/products/p_odg.html 
  http://www.simple.at/
  http://www.datacast.at/technology.html

  We are looking at the MDP/NORM UDP-based file transfer protocol and
plan on using it to transfer files from the Space Shuttle payload
bay on STS-107 (scheduled to launch on July 19th but may be slipping 
right now).

  The bottom line is we want to use standard IP/UDP/TCP protocols that
are supported in every operating system available.  Using a modified
TCP requires more software support that creates more problems when
you are building and deploying operational control centers and 
level-zero processing systems.  We really prefer to use standard
protocols at layer 4 and below and do any space specific tweaks
in the application layer.

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  Keith Hogie                   e-mail: [e-mail]
  Computer Sciences Corp.       office: 301-794-2999  fax: [phone]
  7700 Hubble Dr.
  Lanham-Seabrook, MD 20706  USA        301-286-3203 @ NASA/Goddard
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