From: simon hart (simon.hart@btinternet.com)
Date: Fri Jul 01 2005 - 17:08:09 GMT-3
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
> 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.
> No violate action, therefore take exceed action -
> which is drop the remaining packet.
>
>
> Example 3
>
> This time we have no violate action and the exceed
> action is set-dscp to af13
>
> exceed-action set-dscp-transmit af13
>
> 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 - transmit with dscp of af13
>
> 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
> -
> transmit with dscp of af13
>
> 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 - set dscp of af13
> No violate action, therefore take exceed action -
> which is transmit with dscp of af13
>
> In this example it should be clear that the class is
> no longer policed as all traffic is transmitted,
> however the out of contract traffic (everything
> above
> cir) will be marked as af13.
>
>
> Example 4
>
> One final example to round this off.
>
> We shall use an exceed action that sets dscp and a
> violate action that drops packets
>
> exceed-action set-dscp-transmit af13
> violate-action drop
>
> 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 - transmit with dscp of af13
>
> At Tc2
> Offered packets 10
> In contract first 8 packets - transmit
>
=== message truncated ===
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