RE: ATM Cell Rates

From: Menga, Justin (Justin.Menga@xxxxxxxxxx)
Date: Sun Oct 28 2001 - 17:06:21 GMT-3

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Yes, I understand that, I am just interested in what the IOS calculates as
the cell rate.

If I configure 1024Kbps as the SCR, does Cisco IOS calculate the cell rate
as 2415 cells/sec (1024*1000/[53*8] - this is the cell rate using a 53-byte
cell)
Or does Cisco IOS calculate the cell rate as 2666 cells/sec
(1024*1000/[48*8] - this is the cell rate using a 48-byte cell)

>From testing, I believe it is on the first (using a 53 byte cell)...

Regards
Justin Menga CCIE #6640
Network Solutions Architect
Wireless & E-Infrastructure
Compaq Computer New Zealand
DDI: +64-9-918-9381 Mobile: +64-21-349-599
mailto: justin.menga@compaq.com
web: <http://www.compaq.co.nz/> http://www.compaq.co.nz

-----Original Message-----
From: edgar feliz [mailto:ejfeliz65@yahoo.com]
Sent: Friday, 26 October 2001 9:02 a.m.
To: Menga, Justin; ccielab@groupstudy.com
Subject: Re: ATM Cell Rates

These numbers are what you suscribe to when you order ATM service. Your PCR
is usually your port speed, in FR/ATM this is usually the FR port speed,
the SCR is like the CIR in FR. If you configure with the PCR greater the the
SCR then you can burst, if you PCR=SCR then you can not burst.

"Menga, Justin" <Justin.Menga@compaq.com> wrote:

Does anybody know (preferably with URL proof) how the peak cell rate and
sustained cell rate are calculated from the bandwidth parameters you enter
in IOS configuration.

E.g.

Interface atm1/0
pvc 1/100
vbr-nrt 1920 1024 32

Above, the PCR is 1920 Kbps, the SCR is 1024 Kbps, and the Maximum Burst
Size (MBS) is 32 cells.

To calculate the actual cell rat:

Does IOS divide the bandwidth (Kbps) by 424 bits (This is a single 53-byte
ATM cell)?

Does IOS divide the bandwidth (Kbps) by 384 bits (This is 48 bytes, which is
the data payload of an ATM cell)?

I just need to match up parameters with service provider equipment that
talks cell rates, not Kbps rates. (There probably is a show command that
will show me this, but I don't have access to the customer site).

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