[AG-TECH] RE: CALL FOR REVIEW OF DOC-AGNode Minimum Requirements
Markus.Buchhorn at anu.edu.au
Tue Mar 12 17:30:51 CST 2002
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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