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omz Rising star
Rising star

QoS policing

Hi 

In a lab task, asked to use the CIR value of 64 Kbps and PIR value of 128 Kbps to configure policing. 

police cir 64000 bc xxx pir xxx be xxx

How do we calculate bc, pir and be values?

Thank you

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Hall of Fame Expert

Re: QoS policing

Hello Omz,

if the time was 1 second

bc would be 64000 bps /1s /8bits/byte = 8000 bytes

so 40% of 8000 bytes are : 800 * 4 = 3200 bytes

 

be would be 128000 bps /1s/8bits/byte = 16000 bytes

so 40% of 16000 bytes is 1600*4 = 6400 bytes

 

remember they provide you the time interval but they don't tell you about the bits to bytes conversion :)

 

Hope to help

Giuseppe

 

4 REPLIES 4
Hall of Fame Expert

Re: QoS policing

Hello omz,

the PIR is 128000 bps and it is alredy given

bc and be should be in bytes and are the token buckets.

When bc and be are not set they are calculated based on cir and pir values accomodating for the bytes in 250 msec or 500 msec at cir or pir bit rate.

bc = CIR / 32    be = PIR /32   for time = 250 msec -> 4 and 8 bits/byte

 

Look for three color two rates policer.

 

be is actually filled by the difference between PIR and CIR rates

if a packet is conforming the Xp bytes of the packet are removed from both be and bc

if Xp < available bytes of Bc buffer   (conform action)

if Xp is > then Size of XBc    and Xp < XBe Xp bytes are removed from Be token bucket only  (violate action)

if Xp > Xbe the packet is dropped (exceed)

 

Hope to help

Giuseppe

 

 

 

Hope to help

Giuseppe

 

omz Rising star
Rising star

Re: QoS policing

Hi Giuseppe

Thanks a lot for the reply. Yes PIR is already given I overlooked.

I am trying to understand that the lab task says - 

use the values of CIR*400ms (64000 * 400/1000) and PIR*400ms (128000 * 400/1000) for normal and excess burst sizes

police cir 64000 bc xxx pir xxx be xxx

Solution - police cir 64000 bc 3200 pir 128000 be 6400

How does solution calculates bc=3200 be=6400?

Thanks 

Highlighted
Hall of Fame Expert

Re: QoS policing

Hello Omz,

if the time was 1 second

bc would be 64000 bps /1s /8bits/byte = 8000 bytes

so 40% of 8000 bytes are : 800 * 4 = 3200 bytes

 

be would be 128000 bps /1s/8bits/byte = 16000 bytes

so 40% of 16000 bytes is 1600*4 = 6400 bytes

 

remember they provide you the time interval but they don't tell you about the bits to bytes conversion :)

 

Hope to help

Giuseppe

 

omz Rising star
Rising star

Re: QoS policing

Hi Giuseppe

Thanks a lot for the explanation .. that makes me feel stupid now .. I should have thought more about it :)

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