[nsp] Calculating ATM Cell transfer rates

Alex Foster afoster at gammatelecom.com
Wed Feb 25 12:45:39 EST 2004

That now makes sense - will look at the debug to get 
a true feel.  To your knowledge do most vendors base 
their kbps on 53 byte cells - I mainly use Marconi
ATM products that require rates in cps not kbps -
makes life much easier. 



-----Original Message-----
From: sthaug at nethelp.no [mailto:sthaug at nethelp.no]
Sent: 25 February 2004 17:06
To: afoster at gammatelecom.com
Cc: cisco-nsp at puck.nether.net
Subject: RE: [nsp] Calculating ATM Cell transfer rates

> surely this would give you an inaccurate Cell rate - if
> we wanted to shape a PVC for 256Kbps - using Ciscos
> interpretation this would give you a cell rate of 603 cps
> based on 53 byte cells.  But 603 cps is only 231Kbps of
> actual payload data based on 48 bytes of payload per cell.
> Or am I mis-understanding the whole calculation process?

I am saying that the Cisco specification in kbps is based on 53 byte
cells. Thus if you want 256 kbps of *payload*, you have to specify
256*53/48 = 282 (or 283 if you round up) kbps in your Cisco router

As I mentioned, you can check this yourself by using suitable debug

Steinar Haug, Nethelp consulting, sthaug at nethelp.no

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