Re: QOS Bc Be and Tc

Hi Experts,

I believe I have something to correct regarding the Be concept I spoke of.
Well let me put it this way..Let us for say assume that I have a Bc (CIR/Tc)
8000 bits (these are the bits I can send every interval let us suppose Tc
=125 ms. Thus In one sec I can send 64000 bits and in 30 seconds for example
I can send 64000*30=1920000 bits. Let us suppose for instance, that I didn't
send for a 30 second interval, thus I have wasted this amount of bits
(1,920,000) bits, and now a new interval has come Tc. How much I can send in
this interval? Well just by looking @ it I would say that I can send my Bc(
dedicated for this Tc) as well as my account (1,920,000) which I have wasted
over my last 30 second interval. However let us suppose that the AR of the
interface is 1024 kbps. Thus the maximum number of bits I am allowed to
transfer in terms of the interface capability is 1024kbps/8=128000 bit/Tc
(64000 already the Tc for the interval) and a maximum I can add of 64000
bits.(Compare this to my account 1,920,000 bits). Thus my account will be
re-deposited within 30 seconds where every Tc I can add 64000 bits to my Bc
as a Be value. Note I think if the AR limitation didn't exist for instance
in a scenario, the account will be re-deposited fully in a single Tc.

I would like to thank Carlos G Mendioroz for shedding the light on this, and
Kambiz Aghian who explained it in the link sent by Carlos.

Thank You:)

Best Regards,

KJ

On Wed, Aug 18, 2010 at 11:11 PM, Carlos G Mendioroz <tron_at_huapi.ba.ar>wrote:

> Take a look at
>
> http://news.groupstudy.com/archives/ccielab/200207/msg01417.html
>
> or
>
>
>
http://www.2bccie.com/cisco-certification/ccie-shaping-and-calculating-be-val
ue-for-a-30-second-burst.html
>
> Have your own conclusions...
> -Carlos
>
> karim jamali @ 18/8/2010 17:02 -0300 dixit:
>
>> Hi Carlos,
>>
>> You may be right..i will check the archives. However I also checked Petr's
>> document and found the following formula:
>> PIR = CIR*(1+Be/Bc). By looking @ this formula one can also see the
>> relationship between PIR/Be.
>>
>>
>> http://blog.ine.com/2008/08/26/understanding-the-shape-peak-command/
>>
>> I will be checking, please if you have a good reference will appreciate
>> it!
>>
>> Thanks man:)
>>
>>
>>
>> On Wed, Aug 18, 2010 at 10:54 PM, Carlos G Mendioroz
<tron_at_huapi.ba.ar<mailto:
>> tron_at_huapi.ba.ar>> wrote:
>>
>> Please check your knowledge with a simple test.
>> Search GS archives for discussions on this. Be can actually be
>> transmitted over many Tcs.
>>
>>
>> You can not enforce a PIR with Tc,Bc and Be. You need PIR to be
>> explicit.
>>
>> -Carlos
>>
>> karim jamali @ 18/8/2010 16:50 -0300 dixit:
>>
>> Hi Carlos,
>>
>> I know Bc/Be are both amounts of data..But as per my knowledge
>> Bc/Be does need to happen in a single Tc and they relate
>> directly to CIR/PIR; they are in fact the amount of data that
>> can be sent during one Tc interval.
>>
>>
>> http://qospf.wordpress.com/2008/06/01/ccie-cert-guide-notes-qos-part-iv/
>> *Be = Tc * (PIR  CIR);
>>
>> *The maximum Be is in fact found by replacing the PIR by the AR
>> (Access Rate of the interface).
>>
>> Best Regards,
>>
>> On Wed, Aug 18, 2010 at 10:41 PM, Carlos G Mendioroz
>> <tron_at_huapi.ba.ar <mailto:tron_at_huapi.ba.ar>
>> <mailto:tron_at_huapi.ba.ar <mailto:tron_at_huapi.ba.ar>>> wrote:
>>
>> Karim,
>> Be does not need to happen in one Tc, as your message implies.
>> Also, Be is not a rate, is just an ammount of burst.
>> That's the difference between one rate and two rate policers,
>> and so PIR is not directly related to Be.
>>
>> -Carlos
>>
>> karim jamali @ 18/8/2010 16:20 -0300 dixit:
>>
>> Hi Masroor,
>>
>> Well the simplest and easiest way to think about it
>> (whether with
>> policing/shaping) is that you are connected via a
>> Fastethernet
>> interface to
>> a provider (however most probably you won't have 100 Mbps
>> bought
>> from the
>> provider), and one thing about interfaces they are either
>> ON or
>> OFF. So you
>> can tell it please only send 2 Mbps or 3Mbps..Thus the
>> only way
>> to control
>> is to turn it ON/OFF in such a manner that you will be
>> sending
>> the rate you
>> already bought.
>>
>> Thus the CIR is what you already agreed upon with the
>> Provider.
>> Bc is the
>> same as the CIR however within a smaller time frame Tc.
>> Suppose
>> for instance
>> you are given 2Mbps (CIR) from a provider, and your Tc is
>> 125
>> ms..Your
>> router will divide this one sec into 8 intervals (each a Tc
>> long) and in
>> that Tc you will be only sending Bc (what is allowed to
>> send in
>> one Tc).
>> However note that to send the Bc you will require only a
>> part of
>> the Tc for
>> instance half. Thus what is actually happening is you are
>> sending for half a
>> Tc, and putting your interface off for another half of the
>> Tc
>> with the aim
>> of getting an average of 2Mbps.
>>
>> Calculation Wise: 2Mbps/1 sec = Bc/Tc=CIR/1sec thus you can
>> calculate the
>> Bc.
>> Then check how much time it takes you to send the Bc
>> (based ont
>> he interface
>> speed).
>> time required= Bc/(Access Rate of interface) = (this time
>> will
>> be definitely
>> less than Tc)
>>
>> Thus in every Tc interval you will be ON for this time
>> required/off for the
>> remaining time. Note that for VOIP applications it is
>> advised
>> that the Tc be
>> small so that your interface doesn't turn off for a long
>> time
>> and break the
>> 150ms rule.
>>
>> Regarding Be, is in fact what happens if you exceed the rate
>> that your ISP
>> has given you..It happens in a way that suppose for one
>> of the
>> Tc intervals,
>> you undersubscribed your utilization, i.e. you didn't
>> reach your
>> Bc limit,
>> the provider might be kind enough to keep you some
>> balance, and
>> in another
>> time you may be allowed to burst above Bc. Thus in one Tc it
>> might be
>> possible that you send (Bc + Be) the Be being the access
>> in your
>> account.
>> Same formulas/same concept with CIR but this time with PIR.
>> Supposing that
>> the ISP tells you I am comitted to serve you 2Mbps but at
>> times
>> you may be
>> allowed to get a peak PIR 3Mbps.
>>
>>
>> Hope this helps..I guess for more information you can
>> refer to
>> INE's blog as
>> Petr's posts are great.
>> http://blog.ine.com/page/3/?s=QOS+Shaping
>>
>> Best Regards,
>>
>> On Wed, Aug 18, 2010 at 9:52 PM, masroor ali
>> <masror.ali_at_gmail.com <mailto:masror.ali_at_gmail.com>
>> <mailto:masror.ali_at_gmail.com <mailto:masror.ali_at_gmail.com>>>
>> wrote:
>>
>> hi,
>>
>> Can anyone explain in easy wordings that what is Bc
>> Be and Tc
>>
>> --
>> Regards,
>> Masroor Ali
>>
>>
>> Blogs and organic groups at http://www.ccie.net
>>
>>
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>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> -- Carlos G Mendioroz <tron_at_huapi.ba.ar
>> <mailto:tron_at_huapi.ba.ar> <mailto:tron_at_huapi.ba.ar
>>
>> <mailto:tron_at_huapi.ba.ar>>>
>> LW7 EQI Argentina
>>
>>
>>
>>
>> -- KJ
>>
>>
>> -- Carlos G Mendioroz <tron_at_huapi.ba.ar <mailto:tron_at_huapi.ba.ar
>> >>
>> LW7 EQI Argentina
>>
>>
>>
>>
>> --
>> KJ
>>
>
> --
> Carlos G Mendioroz <tron_at_huapi.ba.ar> LW7 EQI Argentina
>

--
KJ
Blogs and organic groups at http://www.ccie.net