Re: [ssm] Multicast SSM throughput in 802.11

Peter Gutierrez <peterg@nic.umass.edu> Thu, 20 October 2005 15:01 UTC

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To: "Tiago Sousa" <tmas@dei.uc.pt>
Subject: Re: [ssm] Multicast SSM throughput in 802.11
In-reply-to: Your message of "Thu, 20 Oct 2005 02:36:00 BST." <200510200137.j9K1b3su027487@smtp.dei.uc.pt>
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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.

-- 
Peter Gutierrez  OIT/Network Services  U. Massachusetts Amherst
Voice: 413 545 1606   Fax: 413 545 3203    peterg@nic.umass.edu
Opinions?  "Ain't nobody's business but my own" - Irving Taylor


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