From: Gery Pang (pang_gery@yahoo.com.hk)
Date: Wed Feb 26 2003 - 11:47:57 GMT-3
Joe,
Thank you.
Just to make sure I understand.
>For the example
> > rate-limit input 8000000 16000 24000 conform-action
set-mpls-exp-transmit
> 5 exceed-action drop
> >
> The average rate is 8 Mbps, burst size is 16000 bytes, excess burst size
is
> 24000 bytes.
>
> Your time interval would be :
>
> burst size / avg rate = 16000 * 8 bits / 8000000 bps = 16 ms
>
> which is a reasonable interval for the IOS to work with ( I think ).
For the same example, max. 24000 bytes are allowed in a 16ms interval. With
various burst, he maximum traffic allowed is 8Mbps in any circumstances. If
the input traffic is 8000010 bps, the exceeding 10 bits will be dropped.
Am I right?
Thank you for your help.
Regards,
Gery
----- Original Message -----
From: "Joe Chang" <changjoe@earthlink.net>
To: "Gery Pang" <pang_gery@yahoo.com.hk>
Sent: Wednesday, February 26, 2003 3:00 AM
Subject: Re: burst argument in policy-map and CAR
> Hi Gery,
>
> > Please help to clarify the burst value.
> >
> > In the config
> >
> > policy-map map1 10
> > class class1
> > priority 9600 480
> >
> >
> > Quote from the CD:
> > "The burst argument is used to specify the burst size and, therefore,
> configure the network to accommodate temporary bursts of traffic. The
> default burst value, which is computed as 200 milliseconds of traffic at
the
> configured bandwidth rate, is used when the burst argument is not
specified.
> "
>
> Just to clarify, your quote is from a document about confuring burst size
in
> LLQ:
>
>
http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121newft/121
> t/121t3/dtcfgbst.htm
>
> Note the that bandwidth is in kbps, the burst size is in bytes:
>
> priority bandwidth-kbps burst-bytes
>
> > I assume the policy map will divid 1 second into 5 slots. 480 bytes will
> be the max. traffic allowed in a slot and the max. traffic is 9600 bps, no
> matter what the burst is.
>
> The 200 ms is the default time interval that has been specified for this
LLQ
> implementation of the token bucket algoritm. Because you assigned the size
> of the burst, the time interval is no longer 200 ms:
>
> mean rate = burst size / time interval
>
> time interval = burst size / mean rate
> = 480 bytes / 9600 bps
> = 3840 bits / 9600 bps
> = 400 ms
>
> >
> > Could I use the same logic in CAR?
> >
>
> Yes, CAR also uses the token bucket algoritm.
>
> > For example:
> >
> > rate-limit input 8000000 16000 24000 conform-action
set-mpls-exp-transmit
> 5 exceed-action drop
> >
> The average rate is 8 Mbps, burst size is 16000 bytes, excess burst size
is
> 24000 bytes.
>
> Your time interval would be :
>
> burst size / avg rate = 16000 * 8 bits / 8000000 bps = 16 ms
>
> which is a reasonable interval for the IOS to work with ( I think ).
>
> > If I use the same logic, 16000*8*5 = 640000 bits, which is less than
> 8Mbps.
> > So, how is burst-normal related to the bps value?
> >
> > The document suggest burst-normal is calculated by bps*1.5/8, I
> just want to know the logic behind.
> >
> Here is an explanation of the token bucket algoritm:
>
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fqos
> _c/fqcprt4/1000900
>
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