Fair Queue

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Feb 1st, 2008
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I will be implementing multicasting in our network and wanted to inquire about the implementation of QoS. Currently, QoS isn't implemented on any of the Routers and fair queuing is also disabled on all outbound interfaces. We have about 29 remote sited, some of which are linked via T1 (P-to-P), others via T1 (Frame-Realy), also other ones via DS3(P-to-Point), and the last via DS3(ATM).


My question, should I enable fair queuing on the outbound interfaces with the implementation of multicasting? If I were to enable fair queuing, are there any Caveat I should watch for????


Thanks in advance,

sK


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paolo bevilacqua Fri, 02/01/2008 - 10:30
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Which router typew do you have? WFQ has a certain CPU impact that you must consider.


Usually before WFQ one implements priority for voice and possibly like in your case, shaping for multicast, to prevent a crazy stream from killing the link.



paolo bevilacqua Fri, 02/01/2008 - 11:18
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Hi, with that, you can have WFQ up to 2 mbps links, nothing faster.

In fact, not even without any QoS enabled, the old models can keep up with a DS3.

skhirbash Fri, 02/01/2008 - 12:17
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Thanks for the prompt response. I am failing to understand your explaination. Could you please elaborate a little bit.


Thanks,

SK

paolo bevilacqua Fri, 02/01/2008 - 13:24
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See attached document. The 3640 is rated between 25 and 36 Mbps throughput using 512 byte packets.


A DS3 is much more than that, and is bidirectional. So a 3640 will be unable to fill the pipe even if presented with enough traffic.


Hope this helps, please rate post if it does!


Joseph W. Doherty Fri, 02/01/2008 - 18:04
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Multicast, alone, doesn't really dictate the need for FQ (or QoS). What you should determine is whether there's any significant congestion that will be created when the multicast flow(s) is added to your existing traffic.


If you find that the multicast stream(s) makes some traffic have unacceptable performance, FQ, or a more complex QoS implementation, might be a solution. So might be the addition of bandwidth, or both.


Any caveats with FQ? The only major one is "ordinary" WFQ doesn't usually scale well with links faster than T1/E1 assuming the interface will accept it. FQ with CBWFQ does scale and can be used on almost all router interfaces.

skhirbash Mon, 02/04/2008 - 09:31
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Thanks to everyone for their prompt response!


sK

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