[AG-TECH] Audio cutting out

[Jon Johansson]

We are testing our new room node and are finding that the
audio is cutting out sporadically, sometimes for a couple
of seconds. We've seen this in meetings with other sites
using different nodes and haven't been able to find a cause. 
"Packet loss" seems to be a reasonable guess at the problem
and sometimes we can actually see some loss on Rat's 
Reception quality matrix, but many times there is no
measurable sign of loss.

In the current situation I am running a venue on a 
server under my desk (running RH9). My desktop machine is
running AG 2.1.2 on WinXP and has been stable for months and
I've used for many meetings. I've connected to my venue
server through a 100Mb/s network (actually they are 
directly connected to the same Gig switch but only the AG 
client has Gig ethernet, the venue server has a 100 Mb/s
ethernet card). In order to get a continuous audio stream
I'm running Winamp and I've wired the audio out to the 
mic input so that rat is sending a steady music signal
to the venue.

The room node is on the same subnet and physically close,
with a single gateway between my desktop and the node
equipment. tracert and mtrace from my desktop machine
give the following:

C:\Documents and Settings\jonj>tracert ag-audio

Tracing route to ag-audio.cns.ualberta.ca [129.128.8.205]
over a maximum of 30 hops:

  1    <1 ms    <1 ms    <1 ms  ag-audio.cns.ualberta.ca [129.128.8.205]

Trace complete.

C:\Documents and Settings\jonj>winmtrace ag-audio 233.59.192.5
Mtrace from 129.128.8.205 to 129.128.8.151 via group 233.59.192.5
mtrace: Source & receiver appear to be directly connected
Querying full reverse path...
  0  tyr.cns.ualberta.ca (129.128.8.151)
 -1  cnsgw.ucs.ualberta.ca (129.128.8.1)  PIM  thresh^ 0
 -2  ag-audio.cns.ualberta.ca (129.128.8.205)
Round trip time 0 ms; total ttl of 1 required.

Waiting to accumulate statistics...Results after 10 seconds:

  Source        Response Dest    Overall     Packet Statistics For Traffic
>From
129.128.8.205   224.0.1.32       Packet      129.128.8.205 To 233.59.192.5
     v       __/  rtt    0 ms     Rate       Lost/Sent = Pct  Rate
129.128.8.1     cnsgw.ucs.ualberta.ca
     v      \__   ttl    2         0 pps        ?/0            0 pps
129.128.8.151   129.128.8.151
  Receiver      Query Source


Our network is quite robust and in trying to create additional loss
we started several simultaneous large data transfers, without
affecting the rat audio output noticably.

I don't know where else to look for problems without starting
to dissect RAT itself. Would anyone have suggestions?

Thanks,
Jon.

-- 
Jon I Johansson             *  Research Computing Support
jon.johansson at ualberta.ca   *  Computing and Network Services
Tel.: (780) 492-9304        *  University of Alberta
Fax.: (780) 492-1729        *  Edmonton, Alberta, CANADA