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## Calculating Bc in Policing

Hello,

I am facing difficulty understanding the calculation of both Bc and Be in traffic policing but let's ignore Be for a moment. The below formula is used to determine the number of tokens that are filled in the Bc bucket:

Bc = Current_Packet_arrival_time - Previous_Packet_arrival_time x Polced_rate / 8

Because this formula is used to know the number of bytes (or tokens) in the bucket, this also means that the formula is used to calculate the Bc.

Now, i am confused with another formula that also calculate the Bc if i don't configure it. This is actually done by the router or FR switch.

Bc = (CIR x 0.25 sec) / 8bits/byte

So, which formula shall i use to calculate the Bc in Policing?

In shaping, the Bc calculation is straight forward by using : Bc = Tc x CIR or Shaped Rate

And let's say, if i use the first formula, how can i apply it?

For instance, If the bucket is filled with Bc tokens on packets arrival, then how can i detemine the current packet arrival and the previous packet arrival values? .... the book doesn't give much details about it.

Regards,

AM

2 REPLIES
Silver

## Calculating Bc in Policing

Hi,

Actually everything you said is same.

Tc = basic unit of time = So it is equal to Current_Packet_Arrival_time - Previous_Packet_arrival_time

and Bc is actually Bc = CIR / Tc

and NOT

Bc = (CIR x 0.25 sec) / 8

HTH,

Smitesh

Community Member

## Re: Calculating Bc in Policing

Thanks.

Unfortunately, your comment wasn't correct because maybe you didn't get my goal. Below are the points of conflicts from your side:

1- I am talking here about policing not shaping.

2- And let's say If we talk about shaping then the formula for Bc is Bc = Tc x CIR. So, yours is incorrect.

3- There is no Tc calculation in policing because in policing the calculation is based on packets' arrival. Tc is used in shaping to calculate the sending time per interval for each Bc.

Regards,

AM

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