[AG-TECH] Packet Loss

[Chris Kendrick]

On Tue, 2006-08-29 at 10:54 +1000, Markus Buchhorn wrote:
> Hi Chris
> 
> At 09:55 AM 29/08/2006 +1000, Chris Kendrick wrote:
> >How do I check if it is the local machine having packet loss rather than
> >network packet loss?
> 
> Rough rule of thumb - if you're seeing packet loss and if you're not using more than 30% of the available bandwidth to your interface (just add all the streams together), I'd be suspicious it was local. Check the CPU, if it's more than 30% say, I'd be even more suspicious. Of course, if you have a 1G interface to your machine and a 10M feed into your building I'd look into that a bit more :-)
> 
> Are your audio and video process running on the same machine?

Yes, at the moment I have my audio service running on my display
machine, apparently audio doesn't use up much system resources.

> 
> Ideally you want to get stats from your network switch and your network interface, possibly via snmp, to see the true rates and compare them to what the apps are saying.
> 
> >I did try a different Virtual Venue, but upon looking at the bridge that
> >is available for selection when on unicast at each VV I have since
> >noticed that they both use the same bridge AGSC/Manchester.   If it
> >happens again I will try to set up a testing session with the AG Admin
> >at the other end to try another bridge, unfortunately the people running
> >the AG at 8am there time are not technicians so I couldn't check this
> >straight away.
> 
> Fair enough. It's certainly worth testing - some bridges seem to misbehave after some period of uptime, or just for the fun of it <sigh>.
> 
> >> I'd start with monitoring the traffic very carefully. Did vic show
> >similar drops? You can watch its traffic graphs and generate a nice
> >picture to take to your network folks. You can run things like iperf if
> >you're really keen.
> >> 
> >
> >aahh, ok, I'll take that as, "Use iperf to take a look at network goings
> >on"
> 
> Not quite - it'll give you an idea of the end-to-end performance between an iperf client and an iperf server. If you're running close to the iperf suggested peak (for UDP) then I'd expect loss somewhere. The reasons for loss though can be very diverse, from congestion to errors (dodgy cables) to routing flaps to ... etc. Without a probe point at almost every hop it can be very hard to diagnose.
> 
> >Yes sorry, I forgot to mention that the picture when very blocky and
> >choppy as well, when the audio suffered packet loss.
> 
> Ok, so that is consistent. 
> 
> >VIC has traffic graphs? how do you view them?
> 
> On the thumbnail view, pick a site and click on 'info' - that gives you a set of metrics about that stream from that site.  Click on one of the words to get a strip chart of that metric (e.g. 'kilobits' can be good, though subject to changes in the video content, but it gives you a good long-term view of the rate. Loss shows up quite sharply, but it doesn't tell you where the loss is). 

Ahh, thats nice, another diagnostic to go in my toolbox =)

> 
> >Our bridge is on the same subnet as our AG Nodes.  So if the AG node
> >can't to multicast to the Bristol VV neither can our bridge.  We are not
> >on AARNET.  We are on Grangenet.  I don't know if Grangenet peers to
> >JANET.  But when I go to the Bristol VV I don't get any audio/video
> >feeds if I don't switch to unicast.
> 
> GrangeNet peers with with the international networks via AARNet (in Sydney), which includes the international multicast feed. So I'm not totally sure why you're having an issue. However, I've had similar problems with Oxford. Interestingly very few problems with US sites, who should be on the same path. I wonder if the new western route from AU to EU is causing us grief...
> 
> Cheers,
>         Markus

Thanks Markus, and others who have replied.

The e-mails have given me a heap of great new Insight/Tools to be able
to further diagnose AG connectivity issues with.

Chris Kendrick
VPAC

> 
> 
> Markus Buchhorn, ANU Internet Futures             |Ph: +61 2 61258810
> Markus.Buchhorn at anu.edu.au                        |Fx: +61 2 61259805
> The Australian National University, Canberra 0200 |Mob: 0417 281429
>