Cir & Cbs in qos-profile

Created: Dec 4, 2019 10:32:28Latest reply: Dec 6, 2019 08:54:10 189 12 0 0
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Hi everyone,


if we have cir=35Mpbs then default vlaue  of cbs is  546875  how to calculate this?   as i am applying same formula  cir*187 =(?) bytes

35000Kpbs*187=6,545,000,000 bytes= 6545000000*8 bits=52,360,000,000‬ bps not equal to above vlaue?

can anyone explain me how to calculate cbs from cir?



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Featured Answers
DDSN
Admin Created Dec 4, 2019 11:16:53 Helpful(0) Helpful(0)


Specifies the committed burst size (CBS). The value is an integer that ranges from 1500 to 4294967295, in bytes. This parameter is optional. If the PIR is not set, the default CBS is 188 times the CIR. If the PIR is set, the default CBS is 125 times the CIR.
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LSA
LSA Created Dec 4, 2019 13:19:07
thanks for reply,,,,,but if we have 35Mbps cir then how you calculate CBS ,,kindly share complete details.  
All Answers
jason_hu
jason_hu Admin Created Dec 4, 2019 10:49:11 Helpful(0) Helpful(0)

Hi@LSA 
What does the 187 mean? Can you share your command

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DDSN
DDSN Admin Created Dec 4, 2019 11:16:53 Helpful(0) Helpful(0)


Specifies the committed burst size (CBS). The value is an integer that ranges from 1500 to 4294967295, in bytes. This parameter is optional. If the PIR is not set, the default CBS is 188 times the CIR. If the PIR is set, the default CBS is 125 times the CIR.
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LSA
LSA Created Dec 4, 2019 13:19:07
thanks for reply,,,,,but if we have 35Mbps cir then how you calculate CBS ,,kindly share complete details.  
Sprout
Sprout Created Dec 4, 2019 13:47:09 Helpful(0) Helpful(0)

hello,
How you get the value 546875?
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LSA
LSA Created Dec 4, 2019 13:52:01
this is defualt but my question is how to calculated this value from cir.?  
Sprout
Sprout Reply LSA  Created Dec 4, 2019 14:23:52
Where are you see this default value? If you are using AR routers, as 3# said, if the PIR is not set or the PIR and CIR are the same, the CBS is 188 times the CIR. So the Cbs=188 * 35*1024=6,737,920  
LSA
LSA Reply Sprout  Created Dec 5, 2019 08:19:02
@Sprout thanks then its means for CIR =35 Mbps == 6737920 bytes == 6737920 *8==53,903,360bits==53.9Mbps ......... means for 35Mpbs we have 53 Mpbs Burst rate(CBS) this is very big difference,,how it possible..? kindly explain this. Thanks in advance  
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chenhui
chenhui Admin Created Dec 6, 2019 01:48:55 Helpful(0) Helpful(0)

@LSA hi, I'm not sure what you mean the difference.
what's more, where did you get the default CBS value 546875?
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LSA
LSA Created Dec 6, 2019 04:39:30
@chenhui i Know the basic calculation of CDB as CBS=188*PIR but for this====>>> for CIR =35 Mbps == 6737920 bytes == 6737920 *8==53,903,360bits==53.9Mbps ......... means for 35Mpbs we have 53 Mpbs Burst rate(CBS) this is very big difference,,how it possible..? kindly explain this. is this right?  
chenhui
chenhui Admin Created Dec 6, 2019 07:47:05 Helpful(0) Helpful(0)

@LSA hi,
well, actually, I think you are wrong. You mixed up the byte and bps.
for CIR=35Mbps, the default CBS would be 35*1024*188=6737920bytes.
CBS indicates the size of the packet, while CIR indicates the rate of the traffic, they have two different units. you cannot equalize them.
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LSA
LSA Created Dec 6, 2019 08:16:35
THANKS @chenhui according to my understanding CBS is the margin(extra) of acutal bandwidth i-e if we have cir 35Mbps but comming traffic on interface is 37Mbps more then 35Mpbs then the margin wolud be applied as cbs Value...correct me if i m wrong. Please.  
chenhui
chenhui Admin Created Dec 6, 2019 08:54:10 Helpful(0) Helpful(0)

@LSA hi,
er, actually you are wrong.
CBS restrict the packets size, for the burst traffic, it's restricted by the PIR(peak information rate).
In your situation, the CIR is 35Mbps, PIR is 37Mbps.


the post below might be helpful.

https://forum.huawei.com/enterprise/en/token-bucket-introduction/thread/574398-863

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