[AG-TECH] RE: CALL FOR REVIEW OF DOC-AGNode Minimum Requirements

Markus Buchhorn Markus.Buchhorn at anu.edu.au
Tue Mar 12 17:30:51 CST 2002

G'day Ivan

At 08:45 AM 12/03/2002 -0600, Ivan R. Judson wrote:
>It's going to get confusing to reply to your note, since it's been back and
>forth.  I'm wondering how to do this more efficiently.  Until I figure that
>out, I'm going to continue with the method of putting my comments inline
>:-).  Try to decode this one:

Ah, it's not too bad (yet) :-). Take some of those hoax virus email 
warnings that have been round the traps for 30+ iterations (and nobody 
thinks about cutting the headers <sigh>).

>Yep, you are correct here.  I *think* encode latency is pretty constant
>latency (not looking at code, just trying to imagine the easiest way to do
>it), but the decode depending on the playout issues does vary.  One caveat
>to my own statement is that FEC'ing adds significant latency (I hear).

I haven't tested that myself, but I've heard similar comments. In the case 
of pure packet replication, that makes sense (the sample is sent a second 
time and is already one-sample-length later than the original transmission).

>At the retreat there was discussion that the numbers we're quoting are from
>literature that's fairly old and focused on telephone systems.  The fact
>that we'er distinguishing ourselves fairly clearly from a single two person
>audio channel might have a significant impact on the audio latency
>requirements (audio queues, even if skewed might make slightly more latency

Good question. It may come down to the type of interaction you are working 
on. A p2p conversation feels natural if you can interrupt each other and 
get immediate reactions - so low latency and full-duplex are critical. For 
a lecture you can tolerate putting up your hand and waiting for a reaction 
(well, most of us can :-) ).

>There might be a good experiment in trying to construct a measurement of
>audio/video latency is a multistream system and discovering what the
>tolerable amounts are.  Then it could be compared to the literature and
>perhaps we'd discover something!

That's an interesting idea. There'd be some many variables you could play 

Is there a tool around that can take an audio stream and apply arbitrary 
(user-specified) buffering to it before playing it back out on the network? 
Perhaps also apply user-specified jitter, and loss? I've had a request for 
something like this from another project.

> > What happens when we get an AG on the ISS, or run it between sites over a
> > satellite link? (On the ISS the latency would vary over each orbit :-) ).
>I'm hoping to bring my family on vacation to the ISS soon after...

I want to be the Node Op :-)

>Your point is a good one, will you help me craft it into the document so
>it's correct?  feel free to edit the word document and send it back with
>your changes.  I'd be happy to incorporate this idea since it makes alot of
>sense from many different angles.

Ok, will do. Stay tuned.

> > <tangent>
> > Could we perhaps develop a test suite, with things like networked (i.e.
> > non-local) loopback tests and stress-tests, that AGN's have to pass to be
> > 'certified' true, Tier-1, Grade-A AGN?
> > </tangent>
>HEAR HEAR.  This is a great goal.  I'd love for someone to take this up and
>work on it.  Bob Olson has been developing some tools for this on the audio
>side, the video is a bit harder, but could be done as well.  Then the
>network tools would make sense to determine network issues.  The last part
>is the software verification suite, which just inventories and reports
>software version mismatches.

I might have a look at writing something that turns a video stream into 80 
copies and sends them to a multicast group from 80 different sources. 
Should be just a packet rewrite problem, right? At least it's all UDP :-) 
(or maybe hack into vic's network transmission code.... ugh.)

>Waffling, you just got yourself nominated for "Most Feedback of the Year"
>award, if I didn't already know a Joe Feedback, I'd dub you Joe.  Seriously,
>this is awesome feedback, I'd love *more* of it.  Only, let's not make
>Markus have to write it all :-)

<blush> :-) I just finished a large project, so I'm now catching up on all 
my other favourite projects. Plus this stuff is one of my direct research 
interests, so it's not just work ;-)


Markus Buchhorn, Information Infrastructure Services,   | Ph: +61 2 61258810
Markus.Buchhorn at anu.edu.au, mail: CompSci,CSIT Bldg #108|Fax: +61 2 61259805
Australian National University, Canberra 0200, Australia|Mobile: 0417 281429

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