Re: [ssm] Multicast SSM throughput in 802.11

Tiago Sousa <tmas@dei.uc.pt> Thu, 20 October 2005 17:08 UTC

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Subject: Re: [ssm] Multicast SSM throughput in 802.11
From: Tiago Sousa <tmas@dei.uc.pt>
To: Peter Gutierrez <peterg@nic.umass.edu>
In-Reply-To: <200510201500.j9KF0oBl022442@troy.oit.umass.edu>
References: <200510201500.j9KF0oBl022442@troy.oit.umass.edu>
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Hello to all.

Thanks for the reply. I extend the gratefulness to the others that had
answered. 

My wireless access point is configured to send traffic at rate of 54Mbps
(802.11g) although my mobile node receives at 11Mbps (802.11b). So, if i
understand well your suggestion the Basic Rate settings are well
implemented because it is only specified 54Mbps in the AP. Am i correct?

I didn't understand the suggestion of Gaurav: Profiled TCP. Can you
explain better? The multicast throughput (UDP based) can also depends of
the TCP profile? 

The suggestion of Matthias: check in the AP if the multicast rate is
limited. I've been in the web-based interface and i didn't find any item
that refer to multicast. I am using a Belkin 54g AP.

My opinion is that the problem must be in the AP because the outgoing
interface of the access router sends traffic at 4 Mbps. The only thing
in the middle, between the router and the MN, is the AP. So, the
throughput must be affected by some item in the AP. 
I've confirmed all the possible items in the AP and i didn't find any
related with multicast...   

Do you have more suggestions?

Thanks to all.


Tiago Sousa

Qui, 2005-10-20 às 11:00 -0400, Peter Gutierrez escreveu:
> tmas@dei.uc.pt wrote:
> > I am testing the PIM-SSM daemon (both freebsd and linux) and mrd6
> > program in a wireless link. 
> > 
> > The problem I encountered, with both pim6sd daemon and mrd6, is that
> > I'm sending multicast traffic at 4 Mbps and the throughput reaches the
> > mobile node (which is very near from de access point) rounding 40
> > kbps.
> > 
> > I am using the mad-flute tool to send the multicast SSM traffic and
> > the tcpdump plus trpr to analyze the data.
> > 
> >  
> > 
> > Anyone knows why the throughput decreases so much in the wireless
> > link? 
> > 
> >  
> > 
> > I would appreciate any help/hint that helps me to explain these
> > results. 
> 
> Although it should not have the effect of limiting traffic to 40kbps, 
> don't forget that multicast frames must be transmitted at a rate that 
> is included in the Basic rate set according to the IEEE 802.11 
> specification. The basic rate set usually includes 1Mbps, not the 
> 11Mbps or even 54Mbps (in 802.11g radios) that your client may claim to 
> be its rate (which it is for unicast traffic).
> 
> You may want to try removing the lower rates from the Basic set on the 
> access point, to see if your throughput increases, if this is in a test 
> environment. If a client does not support the Basic rate, it will not 
> associate.
> 


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