All things related to multicast

["Marshall Eubanks" <>]

Hello;

I suspect that some router, switch  or link is overloaded or misconfigured, 
and you need to find it. If you are really losing anything like 50% of your 
UDP packets, then TCP
should be very bad too. 

Note, however, that  a misconfiguration could (for example) send all 
multicast through the router
CPU, or put it on a queue, causing losses not present in unicast TCP.

I have also seen problems a lot where the router drops (say) 1 second of 
packets every few 10's of
seconds. TCP with a big buffer can cover this up, while UDP multicast can't. 
A very  bursty
application that blasted your links intermittently might also do this. It's 
not 50% loss, but it
might be 10% or 5%.

Some basic ideas :

Check to make sure your router CPU loads are reasonable. 

If a wireless LAN is involved, many have default limits on the Multicast
bandwidth. (Apple airports do, for example.)

What I generally do to start is to get rtpdump or rtpqual on a laptop, and
see how it is near (on the same LAN as) the source, in the middle, at the 
edge, and
see where the packet loss is occuring. 

Also, many receivers (like Quicktime) have the ability to plot packet loss. 
If you can use
Quicktime, these plots are nice, as they will show if there is any pattern to 
the losses. 
If, for example, the
losses are quasi-periodic, look at router CPU when the losses are high.

Good Luck !

Regards
Marshall Eubanks


On Thu, 1 Sep 2005 14:32:01 -0400
 "Prashant Chopra" 
<>
 wrote:
> Colleagues,
> 
> Problem Statement 
> We have 6 multicast streams running at 1.6 Mbps. Clients connected to the
> leaf nodes are receiving really bad signal - very bad that there are more
> lost packets than received packets. Unicast works okay - transport is TCP
> not UDP. With Multicast, at a single hop from the server, clients receive
> everything just fine - no packet loss. This indicates that server is sending
> all the packets. But at the leaf nodes, things fall apart.
>  
> Question to Everybody
> > Do any of you have any experience of best practices with ToS settings on
> the streaming server (Microsoft) and/or QoS settings on the networking
> side(Cisco)?
> 
> Our Troubleshooting Path
> We are doing some troubleshooting by trying out RTSPU to find out if there
> is a generic UDP issue instead of a Multicast UDP issue. This won't help
> much in resolving the issue, but might help isolate the scope of the
> problem.
> 
> Regards,
> Prashant Chopra
> Chief Architect
> CampusEAI Consortium
> 1940 East 6th Street, 11th Floor
> Cleveland, OH 44114
> Tel:  216.589.9626
> Mobile: 216.402.4505 
> Fax:  216.589.9639 
> Conference Line: 319.643.7750  Pin: 117423#
> www.campuseai.org 
> 
> 
> -----Original Message-----
> From: Alan Crosswell 
> [mailto:]
>  
> Sent: Wednesday, August 31, 2005 7:18 PM
> To: Prashant Chopra
> Subject: Re: Multicast QoS
> 
> Nope.  You could send your question to 
> 
>  though
> /a
> 
> Prashant Chopra wrote:
> > Alan,
> > 
> >  
> > 
> > I was wondering if you are familiar with anyone that is knowledgeable 
> > about Multicast QoS.
> > 
> >  
> > 
> > Regards,
> > 
> > Prashant Chopra
> > 
> > //Chief Architect//
> > 
> > **CampusEAI Consortium**
> > 
> > 1940 East 6th Street, 11th Floor
> > 
> > Cleveland, OH 44114
> > 
> > Tel:  216.589.9626
> > 
> > Mobile: 216.402.4505
> > Fax:  216.589.9639
> > Conference Line: 319.643.7750  Pin: 117423#
> > www.campuseai.org <http://www.campuseai.org/>
> > 
> >  
> > <mailto:>
> > 
> >  
> > 
>