policing and excess burst

[wjackson]

I have been given the task of setting the following up

a 40Mbps CIR and a peak of 60Mbps on a FE interface.

Having read here about the BC value and seeing that I want a 50ms time slice, I have done the following:

40mbps = 41943040 bits

41943040 / 20 = 2097152 bits in a 50ms slice

2097152 / 8 = 262144 bytes in that 50ms slice

the problem I have is to work out the burst properly.

do I do the same calculation but at 60Mbps for the be value?

[pkhatri]

Hi,

To achieve a peak rate of 60Mbps, which is 50% more than your CIR, you will need a Be of 0.5 *Bc. In your case, that gives you:

262144 * 0.5 = 131072 bytes

The idea is that in a 50-ms interval, you can accept up to Bc+Be bytes:

Bc + Be = 262144 + 131072 = 393216

That means that within that interval, you will get a throughput of:

PIR = 393216 * 8 / 0.050 = 62914560 bps.

Just an aside: in data comms, 40Mbps is typically treated as 40,000,000 bps.

Hope that helps - pls rate the post if it does.

Paresh

[pkhatri]

I should also add that in your case, Bc will be 262144 bytes and Be will be 131072 if you are using class-based policing.

If you are using CAR, the Be is inclusive of Bc so it would be 393216 bytes.

Hope that helps - pls rate the post if it does.

Paresh