[AG-TECH] VenueServer Multicast/Unicast Question

Andrew A Rowley Andrew.Rowley at manchester.ac.uk
Thu Apr 6 06:45:34 CDT 2006


This is a good question, but one which I don't really have an answer to!

This may be down to how the individual tools actually work.  I believe that RAT sends out packets using a buffer, so that there is an approximately constant stream of packets, whereas I think that VIC has no such buffer, and so it may send out a mass stream of packets at once, and then send nothing until the next frame is available.  This would imply that it is the buffering on the router that may be at fault here (apart from the fact that VIC is not sending out as it should).  Perhaps increasing the incoming buffer size for multicast packets would help?

This would also agree with the theory that the multicast packets are being treated with a lower priority, since they will presumably be put to the end of the buffer and therefore be thrown out if a higher priority packet comes in.

I should confess that I am not an expert in routers, so I don't actually know if the above could happen.  However, from the analysis, it would appear to be a problem specifically with incoming multicast packets getting to the bridge.  This behaviour would also be consistent with the bridge server being too overloaded to handle any incoming multicast traffic, although from what I think I know about how QuickBridge works, if the bridge server was overloaded, the multicast people would see losses from the unicast people too, which is why I suggested the problem might be with multicast at the router level.

Andrew :)

Access Grid Support Centre,
RSS Group,
Manchester Computing,
Kilburn Building,
University of Manchester,
Oxford Road,
M13 9PL, 
Tel: +44(0)161-275 0685
Email: Andrew.Rowley at manchester.ac.uk 

> -----Original Message-----
> From: owner-ag-tech at mcs.anl.gov [mailto:owner-ag-tech at mcs.anl.gov] On
> Behalf Of John Hodrien
> Sent: 06 April 2006 11:26
> To: ag-tech at mcs.anl.gov
> Subject: RE: [AG-TECH] VenueServer Multicast/Unicast Question
> On Thu, 6 Apr 2006, Andrew A Rowley wrote:
> > 3) If some use unicast and some use multicast, sometimes those using
> > multicast loose the video stream but keep the audio stream.  Those using
> > multicast get good connectivity as per situation 1.  The bridge server
> must
> > also be sending out good multicast traffic, but is having problems
> receiving
> > the traffic, as shown by the fact that the unicast clients sometimes
> loose
> > video.  This could be due to any number of factors, e.g. the routers
> could
> > be set up so that multicast traffic is a low priority, or multicast
> could
> > just not be set up correctly on the routers.
> Why would the clients not also sometimes lose audio?
> jh
> --
> "A fanatic is a person who can't change his mind and won't change the
>   subject."                                           -- Winston Churchill

More information about the ag-tech mailing list