[Sis-csi] Green book thoughts

[L.Wood at surrey.ac.uk]

>At 04:33 PM 4/18/2006, Lloyd wrote:
>> You can use IP -- and UDP -- and be enhanced.
>
> Enhanced? Seems like you've got a custom, non-standard application running 
> over UDP (which doesn't *do* anything, so presumably that custom 
> application has its own custom reliability built into it?) running over IP 
> which "routes" you from a single processor on the spacecraft over a single 
> link to a single processor located directly in the ground station.

UDP provides per-packet checksums, multiplexing and identification via ports, and a standard widespread sockets interface convention for building on top of.

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.)

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).

ftp://ftp-eng.cisco.com/lwood/cleo/README.html

L.

<http://www.ee.surrey.ac.uk/Personal/L.Wood/><L.Wood at surrey.ac.uk>
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