From: Alexei Monastyrnyi (alexeim@orcsoftware.com)
Date: Wed Oct 25 2006 - 15:05:49 ART
Had to re-read the original question once more :-)
"So what's the point of having a different command ? Isn't it the same
thing if I set shape average with a Bc equal to Bc+Be of shape peak ?"
Setting a new Bc1 as Bc+Be for average is INDEED different from peak
with original Bc and Be. And I think we all said that but via different
words. :-)
A.
Vincent Mashburn wrote:
> I absolutely agree with your statement. However, the problem that I am
> trying to address here is referring to the difference in having a shape
> peak and with a given bc + be or using the shape average and setting the
> bc to the same value as the bc + be in the shape peak. For instance,
> what is the difference in using shape peak with a be of 8000 and a bc of
> 8000, or using shape average with a bc of 16000? The answer is the
> difference in the value of tc. No matter if you are dealing with shape
> average or shape peak, the Tc is always calculated on the bc only. So,
> in the example above, the shape peak tc would be based on a 8000 bc and
> the shape average tc would be based on a 16000 bc. I hope I am making
> sense here.
> Thanks
> Vince Mashburn
> Voice / Data Engineer
> 901-263-5072
> CCVP, CCNP, CCDA,Network +
> Cisco IP Telephony Support Specialist
> Cisco IP Telephony Operations Specialist
>
> -----Original Message-----
> From: Alexei Monastyrnyi [mailto:alexeim@orcsoftware.com]
> Sent: Wednesday, October 25, 2006 12:48 PM
> To: Vincent Mashburn
> Cc: WorkerBee; Cagri Yucel; Group study
> Subject: Re: Shape average and shape peak
>
> I think there is a bit of misunderstanding here.
> You do change Tc via changing Bc for given CIR And CIR is something you
> are going from on the first hand, cause we first define a CIR, from SLA
> for example, and then tweak Tc, if we need, via appropriate Bc.
>
> And this happens with or without Be, with either "shape average" or
> "shape peak". Does it make sense?
>
> In this case Tc is a constant value, if you got a CIR and decided upon
> Bc. I mean you cannot make Tc variable for the given circuit if you
> decided on other parameters, do you?
>
> HTH somehow
> A.
>
> Vincent Mashburn wrote:
>
>> I am not sure where you are getting that Tc is a constant value. I
>> would agree that for a given CIR and Bc, the Tc is constant, but I do
>> not agree if you are saying that Tc is always a defined value. If it
>> were, VoIP would not work. For instance, what if a SP provided you a
>> 10MB link but you only paid for 3MB. You would have to force your
>> traffic not go over 3MB. Also, if utilizing VoIP, you would want to
>> make sure that your Tc was around 10ms. Therefore, you would need to
>> shape.
>>
>> Using CIR = Bc/Tc (Avg), you would need to solve for Bc since you know
>> your values for the CIR and the value you want for Tc.
>>
>> So, 3MB = Bc/10ms ==> Bc = 30000
>>
>> Now, if you are using Shape Peak to use the full 10MB link (Which you
>> would never do in the voice arena), you would have:
>>
>> 7MB = 3MB (1 + Bc/Be) ==> 7Mb = 3Mb (1 + Be\(3Mb * Tc))
>>
>> Let our Tc = 10 ms as in the shape average...
>>
>> Solve for Be ==> 39990
>>
>> However, since Be is randomized, you would always want to set it to 0
>>
> in
>
>> real life scenarios. If you don't, you could have excess jitter.
>>
> That
>
>> is why I always use shape average.
>>
>> This being beside the point, the original point of my post was to
>>
> point
>
>> out the difference between using shape peak with a given bc and be and
>> using shape average and setting the Bc to the same value as bc + be in
>> shape peak.
>>
>> Vince Mashburn
>> Voice / Data Engineer
>> 901-263-5072
>> CCVP, CCNP, CCDA,Network +
>> Cisco IP Telephony Support Specialist
>> Cisco IP Telephony Operations Specialist
>> -----Original Message-----
>> From: WorkerBee [mailto:ciscobee@gmail.com]
>> Sent: Wednesday, October 25, 2006 3:35 AM
>> To: Vincent Mashburn
>> Cc: alexeim@orcsoftware.com; Cagri Yucel; Group study
>> Subject: Re: Shape average and shape peak
>>
>> With either shape average or shape peak, the Tc calculation is fixed.
>>
>> Shape average - CIR = Bc / Tc
>> Shape peak - CIRpeak = CIR (1 + Be/Bc)
>> = Bc/Tc + Be/Tc
>> = 1/Tc (Bc + Be) note : Tc
>>
> is
>
>> constant
>>
>> Use shape average if the CIR must always maintained.
>>
>> Use shape peak if your network allows you to burst above CIR.
>>
>> Be value range from 0 to (Access Rate - Bc).
>>
>> Hence, both commands are meant for different meaning, should not
>> just view it from a mathematically view. It does not work that way.
>>
>>
>> On 10/25/06, Vincent Mashburn <vmashburn@fedex.com> wrote:
>>
>>
>>> It is my understanding that Be only gets transmitted only if excess
>>> bandwidth is available, even in shape peak. So, if your transmitted
>>> traffic totally saturates the entire token bucket at a particular
>>> interval (Tc), then there is no room to use the Be, so the
>>>
> transmitted
>
>>> Be is 0 (the entire Bc is used). However, if the Bc did not take the
>>> entire bucket for that interval, the Be is allowed to be used until
>>>
>>>
>> the
>>
>>
>>> excess bandwidth is used up. Now for Shape average, this Be is
>>> calculated based on the previous intervals (Tc) information whereas
>>>
>>>
>> the
>>
>>
>>> shape peak allows the Be to transmitted based on the current
>>>
> intervals
>
>>> (Tc) information. This is how I understand it. Please add any
>>> additional info to this that you can.
>>> Thanks
>>> Vince Mashburn
>>> Voice / Data Engineer
>>> 901-263-5072
>>> CCVP, CCNP, CCDA,Network +
>>> Cisco IP Telephony Support Specialist
>>> Cisco IP Telephony Operations Specialist
>>>
>>> -----Original Message-----
>>> From: Alexei Monastyrnyi [mailto:alexeim@orcsoftware.com]
>>> Sent: Tuesday, October 24, 2006 12:47 PM
>>> To: Vincent Mashburn
>>> Cc: Cagri Yucel; Group study
>>> Subject: Re: Shape average and shape peak
>>>
>>> Hi Wincent.
>>>
>>> When adding to Bc we definitely increase Tc with the same CIR... but
>>> under the hood... Odom in DQOS Guide says "shape average" behavior is
>>> the same as normal GTS behavior, i.e spending Be after "a long period
>>>
>>>
>> of
>>
>>
>>> inactivity" during which Be is being accumulated, whereas "shape
>>>
> peak"
>
>>> spends tokens from Be on every Tc.
>>>
>>> If we spend tokens from Be at each and every Tc and our traffic
>>>
>>>
>> profile
>>
>>
>>> is not lower than conform rate, i.e >=CIR all the time, where do we
>>>
>>>
>> get
>>
>>
>>> Be accumulated from?
>>>
>>> I have a feeling that this Be is not the same as normal
>>>
>>>
>> traffic-shaping
>>
>>
>>> Be... It is just a sort of extra credit we've got to be able to burst
>>> more at each Tc ... without increasing a Tc...
>>>
>>> Does it make any sense?
>>>
>>> A.
>>>
>>>
>>> Vincent Mashburn wrote:
>>>
>>>
>>>> This is a common question. To answer the question, refer back to
>>>>
>>>>
>> the
>>
>>
>>>> formula: CIR = bc/tc.
>>>>
>>>> For shape peak, bc + be is sent every interval, but the formula is
>>>>
>>>>
>>> still
>>>
>>>
>>>> CIR = bc / tc. For shape average, bc is sent every interval, and
>>>>
>>>>
>> the
>>
>>
>>>> formula is still CIR = bc / tc.
>>>>
>>>> So, say you have a CIR of 64000, bc = 8000 and be = 16000.
>>>> Using shape average:
>>>>
>>>> 64000 = 8000 / tc ==> tc = 125ms.
>>>>
>>>> Using shape peak:
>>>>
>>>> 64000 = 8000 / tc ==> tc = 125ms
>>>>
>>>> Using shape average by setting bc = bc + be
>>>>
>>>> 64000 = 24000 / tc ==> tc = 375ms.
>>>>
>>>> So, as you can see, it is different.
>>>> Hope this helps.
>>>>
>>>> Vince Mashburn
>>>> Voice / Data Engineer
>>>> 901-263-5072
>>>> CCVP, CCNP, CCDA,Network +
>>>> Cisco IP Telephony Support Specialist
>>>> Cisco IP Telephony Operations Specialist
>>>>
>>>> -----Original Message-----
>>>> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
>>>>
>>>>
>>> Of
>>>
>>>
>>>> Cagri Yucel
>>>> Sent: Tuesday, October 24, 2006 4:49 AM
>>>> To: Group study
>>>> Subject: Shape average and shape peak
>>>>
>>>> I am sure I am missing a bit here but on the Cisco Doc it says
>>>>
>>>> shape average sends Bc bits in each interval
>>>> shape peak sends Bc+Be bits in each interval
>>>>
>>>> So what's the point of having a different command ? Isn't it the
>>>>
>>>>
>> same
>>
>>
>>>> thing
>>>> if I set shape average with a Bc equal to Bc+Be of shape peak ?
>>>>
>>>> Thanks
>>>>
>>>>
>>>
>>>
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>
>>
>>
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