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<TITLE>RE: [Sis-csi] Green book thoughts</TITLE>
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<P><FONT SIZE=2>>At 04:33 PM 4/18/2006, Lloyd wrote:<BR>
>> You can use IP -- and UDP -- and be enhanced.<BR>
><BR>
> Enhanced? Seems like you've got a custom, non-standard application running<BR>
> over UDP (which doesn't *do* anything, so presumably that custom<BR>
> application has its own custom reliability built into it?) running over IP<BR>
> which "routes" you from a single processor on the spacecraft over a single<BR>
> link to a single processor located directly in the ground station.<BR>
<BR>
UDP provides per-packet checksums, multiplexing and identification via ports, and a standard widespread sockets interface convention for building on top of.<BR>
<BR>
That's why many custom non-IETF-standard applications, including Skype, Real, and CFDP, use UDP. I presume CFDP also implements its own custom reliability? Is that somehow a bad thing? (No.)<BR>
<BR>
The choice of path from one of a network of scheduled processors on the DMC spacecraft to one of a network of computers in the ground station LAN is dictated solely by pass utilization and wanting to get the most from the space/ground link while it's active, rather than introduce a bottleneck elsewhere with a longer path. That applies no matter what UDP-based protocol you use; a CFDP implementation was used in exactly the same way (until it was replaced to increase performance and link utilization).<BR>
<BR>
<A HREF="ftp://ftp-eng.cisco.com/lwood/cleo/README.html">ftp://ftp-eng.cisco.com/lwood/cleo/README.html</A><BR>
<BR>
L.<BR>
<BR>
<<A HREF="http://www.ee.surrey.ac.uk/Personal/L.Wood/">http://www.ee.surrey.ac.uk/Personal/L.Wood/</A>><L.Wood@surrey.ac.uk><BR>
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