Re: [nsp] telco SCR/PCR and Cisco kbps

From: Gerard White (gwhite@newcomm.net)
Date: Sat May 12 2001 - 06:15:04 EDT


At 08:45 AM 5/12/2001 +0200, sthaug@nethelp.no wrote:
> > Not sure if its been changed in 12.0, but in 11.2, IOS output
> > traffic shaping against ATM interfaces is configured with respect
> > to 48 Byte Cell Payload.
> >
> > Therefore, with your PCR configured for 1536 kbps (kiloBITSpersecond):
> >
> > 1536 * 1000 = 1536000 bits per second
> > 1536000 / 8 = 192000 bytes per second
> > 192000 / 48 = 4000 cells per second
>
>I'm afraid this is incorrect. The Cisco kbps value is converted to cells
>using 53 bytes per cell, not 48. You can verify this for yourself by doing

Ah yes, BUT if you examine his configuration, you will see he is using
an older generation IOS method of ATM provisioning:

= = = = = = = = = = =

interface ATM1/0.37 point-to-point
description 1536 PVC to POP
bandwidth 1536
ip address 1.2.3.4 255.255.255.252
no ip directed-broadcast
atm pvc 1 1 37 aal5snap 1536 1536 100
!
= = = = = = = = = = =

When using this method, traffic shaping rates are with reference to
48 byte cell payload.

GW



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