Re: [colorforth] DARPA takes aim at IT sacred cows

["Samuel A. Falvo II" <kc5tja@xxxxxxxx>]

On Sunday 28 March 2004 09:45 am, Samuel A. Falvo II wrote:
> > packet arrival delays, and/or packet arrival delay variance, is
> > critical?  (Think about trying to stream music or video.  Think
> > about trying to control a robot on the moon from a console on
> > Earth.)
>
> In practice, these issues are moot.  End-points buffer a significant
> (though not necessarily a majority) amount of the stream data before
> even *attempting* to render the data.  As long as packets arrive fast
> enough to keep the buffer filled, that's all the real-time media
> player needs.  It could care less about specific inter-packet delays. 
> And if it does, well, it's clearly not designed at all for fault
> tolerance.  In which case, you get what you pay for.

I actually didn't see the second half of that proposal.  I happened to 
have visited Goddard Space Flight Center, and I happen to know rather 
well how they handle this situation:

1.  They send command data to the remote node, and then, unsurprisingly,
2.  They wait for a response/confirmation/telemetry.

In short, NASA sends precisely *one* packet of data to the remote 
station, waits for the response, then decides what to do based on 
telemetry received thereafter.

There is no other way to do that, AND, the choice of protocol really 
doesn't matter much at all for that.  If you want to send single-byte 
payloads using networks that have 250-byte headers, be my guest.  You 
won't notice any difference in performance.

This is *particularly* true for deep-space probes.

--
Samuel A. Falvo II


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