Greetings.
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
Your Line rate is really 4000 * 53 * 8 = 1696000 bps
Some telco ATM switching gear is configured by specifying
the exact PCR for a customer PVC circuit (in terms of
cells per second - such as the Nortel Passport 7480/15000
series of switches). If you ask for a 1536000 bps circuit,
it may be configured (unfortunately for you) as:
1536000 / 8 = 192000 bytes per second
192000 / 53 = 3622.64 cells per second
Hence, you'll be policed at 3622.64 * 48 * 8 = 1391094.3 bps.
GW
At 02:24 PM 5/11/2001 -0400, Pat Trainor wrote:
>List,
> When the telco gives us a SCR and PCR for our OC-3, we need to
>convert it to kbps to avoid policing violations at their switch. CCO says:
>
>kbps = (cps * 48 * 8) / 1024
>
> cells per second
> 48 bytes (payload) per ATM cell
> 8 bits per byte
> 1024 bits/kbit
>
> ..but there is still a quesiton here concerning the value of 1024
>or 1000 as the bits/kbit value.
>
> Additionally, is the above figure of a full 48 bytes for payload
>still valid when the circuit is a PVC? As in:
>
>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
>!
>
>..with a FR circuit on the other side..
>
>Cisco 3662, ATM card, OC-3, v12.0, ...
>
>TIA!
>
>pat
>:)
>
>http://ptrainor.title14.com
>"While it's true winning isn't everything, LOSING IS NOTHING!" -Ed Bighead
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