Frame Relay LFI Calculations

[Chuck Smith]

OK So I know the formula for find the fragment size which is CIR * Delay / 8 but how do you figure out the portion for the map-class?

Say I have a 384k CIR how do I know what my Bc needs to be set too? I can’t find a clear explanation for this.

[Brandon Buffin]

You configure Bc to force the shaping interval (Tc) that you want. The formula is Tc = Bc/CIR. If your CIR is 384k and you want Tc to be 10ms then Bc would need to be 3840. Please see the following link for confirmation.

http://www.cisco.com/en/US/tech/tk1077/technologies_configuration_example09186a0080101210.shtml#17

Hope this helps. If so, please rate the post.

Brandon

[Chuck Smith]

That is what I found already but if I divide 384000 by 3840 I get 100 not 10. Is Tc measured differently?

[pkhatri · Accepted solution]

Hi,

Given a CIR of 384000bps and a Bc of 3840, the Tc is calculated as follows:

Tc = Bc/CIR = 3840/384000 = 0.01 seconds

0.01 seconds is equal to 10 milliseconds so that is quite correct.

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

Paresh

[Chuck Smith]

Dang I feel like an idiot. You are absolutely right. I kept saying Kilobits in my head when 384000 is bits not kilobits. :) Thanks for the clarification.