Re: WFQ: Rounded packet size

Using packet size for SN increment is crucial for fair-queueing. This
way it allows for bandwidth allocation based on the actual traffic
rate. Clearly, if you add just the weight, you assume all flows have
equal packet sizes.

HTH

2010/4/26 Bit Gossip <bit.gossip_at_chello.nl>:
> Petr and all,
> the formula for active flow from the IEWB below is:
> newSN = previousSN + W * PacketSize
>
> This is very different from the formula in "CCIE Practical Studies
> Volume II" chapter "Chapter 6:
> newSN = previousSN + W
>
> They are profoundly different because the latter doesn't account for
> packet size.
>
> So which is the correct one?
> Thanks,
> bit.
>
>
> On Mon, 2008-12-15 at 15:56 +0300, Petr Lapukhov wrote:
>> Hi,
>>
>>
>> Most likely, the book refers to the "round number" which is the size
>> of the last packet sent by the scheduler. This value is used to
>> initialize every new flow queue byte counter. You can read a detailed
>> description of WFQ algorithm (explaning how this round number is used
>> btw) here:
>>
>>
>> http://www.internetworkexpert.com/downloads/IEWB-RS-VOL-I-V5.Section.10.QoS.teaser.pdf
>>
>>
>> The second task in dedicated to WFQ. Understanding the internal
>> working of WFQ is very important since the same scheduling procedure
>> is used by CBWFQ.
>>
>>
>> HTH,
>>
>>
>> --
>> Petr Lapukhov, CCIE #16379 (R&S/Security/SP/Voice)
>> petr_at_internetworkexpert.com
>>
>> Internetwork Expert, Inc.
>> http://www.InternetworkExpert.com
>> Toll Free: 877-224-8987
>> Outside US: 775-826-4344
>>
>>
>>
>> 2008/12/14 Bit Gossip <bit.gossip_at_chello.nl>
>> Experts,
>> any idea on how these value are calculated for the WFQ min-max
>> algorithm?
>> In "CCIE Practical Studies Volume II" chapter "Chapter 6. QoS
>> b Rate
>> Limiting and Queuing Traffic" there is an example where 60 and
>> 700 are
>> used. But how are these value determined?
>> "During the WFQ process, packet size is noted when new packets
>> arrive.
>> If the IP flow that they belong to is new, a rounded packet
>> size is also
>> used."
>> Tnx,
>> bit
>>
>>
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>>
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>
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>

-- 
Petr Lapukhov, petr_at_INE.com
CCIE #16379 (R&S/Security/SP/Voice)
Internetwork Expert, Inc.
http://www.INE.com
Toll Free: 877-224-8987
Outside US: 775-826-4344
Blogs and organic groups at http://www.ccie.net