[AG-TECH] Access Grid audio bitrate

Ben Juby bpj00r at ecs.soton.ac.uk
Thu May 23 11:02:46 CDT 2002

Is there any reason why the the Access Grid needs to use such high bitrate
audio? Uncompressed 256kbps streams seems a bit excessive for voice

Often in access grid sessions we have observed incoming audio rates of
over 1.5Mbps, and since silence detetection isn't used, most of this is
atrributable to background noise from sites that aren't speaking. 

I realise that the purpose of using 256kbps audio is to make the audio
high qualitiy, but if slightly lower quality and compressed audio was used
the audio bitrate could be drastically reduced, without detracting from
the Access Grid experience.

I also realise that for many sites, this extra traffic may not be an
issue, but for some sites behind software firewalls (including us), this
audio traffic combined with the video traffic can make the firewall
struggle and drop packets. For large meetings, the incoming bandwidth can
be over 6Mbps, and something like 25% of which may be atrributable to
just audio.   

Having such high bitrate audio also seems to put significant processing
load on the machine running RAT to pick up all the network data and play
the streams. Yesterday another member of my department was listening in on
an Access Grid session from their desktop, and were experiencing almost
full CPU utilisation before they had even tried running VIC.

I'd be interested to hear if anybody else has experienced similar issues.


Ben Juby

IAM Research Group
Department of Electronics and Computer Science
University of Southampton
SO17 1BJ

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