Subject: [ssm] Multicast SSM throughput in 802.11

From: "Tiago Sousa" <[email-masked]>
Date: Thu, 20 Oct 2005 02:36:00 +0100

Hello

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.

Thanks.

Tiago Sousa

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From: Matthias Waehlisch <[email-masked]>
Date: Thu, 20 Oct 2005 09:19:53 +0200

Hi Tiago,

  at some access points you can configure rate limiting/a threshold for 
multicast. Because the wlan cell is a shared segment, you have no chance 
to use IGMP snooping, but you want to suppress a 'complete bandwidth 
allocation' by the use of multicast.

regards
  matthias

---

From: Peter Gutierrez <[email-masked]>
Date: Thu, 20 Oct 2005 11:00:50 -0400

[email-masked] 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.
> 
>  
> 

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    [email-masked]
Opinions?  "Ain't nobody's business but my own" - Irving Taylor

---

From: Tiago Sousa <[email-masked]>
Date: Thu, 20 Oct 2005 18:01:16 +0100

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

---

From: Peter Gutierrez <[email-masked]>
Date: Thu, 20 Oct 2005 13:49:11 -0400

[email-masked] wrote:
> 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?
> 
> explain better? The multicast throughput (UDP based) can also depends
> of the TCP profile? 
> 
> 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.
> 
> 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...   
> 

I am not familiar with a Belkin AP, so I can only suggest you determine 
what rates are set as Basic. I can't suggest how you do so.

The access points I use have ssh capabilities, and I can login and 
query about the state of the AP, e.g.,

AP> show controller dot11Radio 0
!
[snip]
Current Rates:  2.0 basic-5.5 6.0 9.0 11.0 12.0 18.0 24.0 36.0 48.0 54.0
Active Rates:  2.0 basic-5.5 6.0 9.0 11.0 12.0 18.0 24.0 36.0 48.0 54.0
Allowed Rates:  1.0 2.0 5.5 6.0 9.0 11.0 12.0 18.0 24.0 36.0 48.0 54.0
Best Range Rates:  basic-1.0 2.0 5.5 6.0 9.0 11.0 12.0 18.0 24.0 36.0 
48.0 54.0
Best Throughput Rates:  basic-1.0 basic-2.0 basic-5.5 basic-6.0 
basic-9.0 basic-11.0 basic-12.0 basic-18.0 basic-24.0 basic-36.0 
basic-48.0 basic-54.0
Default Rates:  basic-1.0 basic-2.0 basic-5.5 6.0 9.0 basic-11.0 12.0 
18.0 24.0 36.0 48.0 54.0

Note that all multicast (and broadcast and control) frames would be 
transmitted at 2.0Mbps on this AP.

Perhaps there is a screen output from the Belkin that displays the 
enabled rates and specifies which are Basic.

Also, you may have better results asking your questions on a different 
list, instead of this ssm specific IETF list. I suggest the Internet2 
multicast working group list, <mailto:[email-masked]?subject=help> 
since you appear to be from an institution that routes to Internet2.