Re: confusing Be formula...

Hi Experts,

Be = Tc * (PIR CIR)

CIR:Comitted Information Rate/what you and the ISP agree upon.
PIR:Peak Information Rate
Bc:It is the CIR per Tc (since the router divides the second into Tcs and in
every Tc you are allowed to send Bc bits as an amount)
Be:It is the PIR per Tc (amount you can send as an excess in one Tc)..

PIR-CIR: is only the excess you are allowed to send. PIR is the whole
amount/CIR:comitted account thus the difference will express the excess per
second.
Be: is always in a single Tc, thus you see the Tc* (PIR-CIR).

Well you might think now where does this excess come from?

Your ISP has given a 64kbps link supposing that the Tc=125ms.

Thus in every Tc you will send Bc=8kb=8000bits
Suppose that for once of the Tcs you didn't send any traffic. Thus the
traffic goes into your balance account and in the next Tc when you have
traffic theoretically you will be able to send what you always do in one Tc
(Bc) and the balance you have in your account (Be)..However note the fact
that if the AR (Access Rate/Speed of your interface) doesn't allow you to
send Bc+Be, the Be will be sent on multiple intervals.

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,

On Tue, Sep 7, 2010 at 1:48 PM, CCIE UY <ccieuy_at_gmail.com> wrote:

> Hi People, im confused about Be calculation and i need to confirm if this
> formula applies only to FRTS or if this applies to GTS and CBTS too:
>
> Anyone, could help me understand this?
>
> Be = Tc * (PIR CIR)
>
> Regards.
>
> Horacio.
>
>
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-- 
KJ
Blogs and organic groups at http://www.ccie.net