From: Sila Moni (silamoni@yahoo.com)
Date: Fri Jul 01 2005 - 17:21:32 GMT-3
Simon,
Once again, thank you for your kindness. Now, I have
a better grip on this. I'll re-read your response to
Gladston a couple of more times. :)
Regards,
Sila
--- simon hart <simon.hart@btinternet.com> wrote:
> Sila,
>
> The Tc is derived by Cir and Bc. Now if you do not
> enter Bc, then there
> will be a default Tc. The Tc will differ depending
> upon which policing /
> traffic shaping algorithm is in use and the line
> rate of interface.
>
> For example, Traffic shaping on Frame relay sub 2Mb
> will default to 125ms,
> Class Based policing will default to 250ms.
>
> Now if you enter Bc for any Traffic shaping or
> policing command you are
> affecting the Tc.
>
> Tc is a product of Bc/CIR
>
> So if we take Gladston's original example of
>
> CIR = 64000 (bits)
> Bc = 8000(bytes) - therefore 8*8000 = 64000 bits
>
> Thus Tc = Bc/CIR = 64000 / 64000 = 1 second
> -------------QED
>
> HTH
>
> Simon
>
> -----Original Message-----
> From: nobody@groupstudy.com
> [mailto:nobody@groupstudy.com]On Behalf Of
> Sila Moni
> Sent: 01 July 2005 18:41
> To: SIMON HART; ccielab@groupstudy.com
> Subject: Re: CB Policing with Be and Without Violate
> Action
>
>
> Simon,
>
> Thanks for the example. This is one of my weakness
> as
> well. I'm still confused on how you calculate Bc
> and
> Be. Normally, I would take 64000 * .125 (default
> Tc). That'll give me 8000. That is my Bc. Then, I
> divide 8000 by 8 or 1000. That would be my Bc.
>
> 1. Is that how the arithmetic being done? Please
> correct me if I am wrong.
>
> 2. How do you determine how many interval to police
> or
> shape?
>
> Lets say you're asked to police 2Mb on r1e0. Based
> on
> what I learn here, I would do the following.
>
> class-map R1E0
> match input-interface e0
> !
> policy-map RATE-LIMIT
> bandwidth 2000 <-- need this or fair-queue
> random-detect
> police 2000000 250000 31250 conform-action transmit
> \
> exceed-action drop
> !
> int e0
> service-policy output RATE-LIMIT
>
> TIA
> Sila
> --- SIMON HART <simon.hart@btinternet.com> wrote:
>
> > Hi Gladston,
> >
> > CB Policing without violate action is valid. Your
> > configs below, however, do not make a great deal
> of
> > sense. I shall try and explain.
> >
> > Police cir 64000 bc 8000 be 1000
> >
> > Now this statement dictates that we can transmit
> > conforming bits at a rate of 64000 bits
> (8000bytes)
> > every second. So our Tc is 1 second. The
> statement
> > also suggests that during any Tc interval of 1
> > second
> > we can send an additional 8000 bits (1000bytes),
> if
> > the be bucket has not been used up.
> >
> > Now in order to explore this further we need to
> make
> > some assumptions. Firstly lets assume that the
> > packets offered are 1000bytes (8000 bits).
> >
> > Therefore for each Tc we can transmit 64000/8000 =
> 8
> > packets that conform.
> >
> > We need to determine the actions for conforming
> and
> > non-conforming traffic
> >
> > so in your config:
> >
> > conform-action transmit
> > exceed-action drop
> > violate-action drop
> >
> >
> > Example 1
> >
> > Now look at what happens as packets are offered
> >
> > At Tc0
> >
> > Bc = 8 packets
> > Be = 1 packet
> >
> > At Tc1 (end of first period)
> > Offered packets 9
> > In contract first 8 packets - transmit
> > Remaining 1 packet - try and use Be
> > Decrement Be by 1 token
> > Take action on Be - in this case drop, therefore
> > packet is dropped.
> >
> > At Tc2
> > Offered packets 10
> > In contract first 8 packets - transmit
> > Remaining 2 packets - try and use Be
> > Be = 0
> > therefore take Violate action - which is drop
> > remaining packets
> >
> > At Tc3
> > Offered packets 5
> > In contract first 5 packets - transmit
> > Because Bc has not been fully used (3 tokens
> spare)
> > We can now add 1 token to Be
> >
> > At Tc4
> > Offered packets 10
> > In contract first 8 packets - transmit
> > Remaining 2 packets - try and use Be
> > Decrement Be by 1 token
> > Take exceed action on Be - in this case drop,
> > therefore packet is dropped.
> > 1 packet now violates - take violate action -
> > therefore drop this packet.
> >
> > Hopefully from the above example you can see that
> Be
> > is not really being used for any purpose. This is
> > because the Be action is the same as the violate
> > action, and hence any non-conforming packets will
> be
> > dropped.
> >
> >
> > Example 2
> >
> > Now see what happens when we remove the violate
> > action
> > on the previous example.
> >
> > At Tc0
> >
> > Bc = 8 packets
> > Be = 1 packet
> >
> > At Tc1 (end of first period)
> > Offered packets 9
> > In contract first 8 packets - transmit
> > Remaining 1 packet - try and use Be
> > Decrement Be by 1 token
> > Take action on Be - in this case drop, therefore
> > packet is dropped.
> >
> > At Tc2
> > Offered packets 10
> > In contract first 8 packets - transmit
> > Remaining 2 packets - try and use Be
> > Be = 0
> > No violate action - however therefore take Be
> action
> > -
> > drop packets
> >
> > At Tc3
> > Offered packets 5
>
=== message truncated ===
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