[c-nsp] atm ubr settings?

[Antonio Querubin]

On Mon, 3 Apr 2006 goemon at anime.net wrote:

> I am arguing with another engineer over provisioning of our customer ATM
> PVCs.
>
> His argument goes something like:
>
> "Configuring every ubr pvc to 45mbps by default does not hurt anything,
> regardless if the customer's circuit is telco provisioned for 256k or
> 1.544mbps or anything else. Therefore, this is a valuable method to
> prevent us from having to waste any time ever configuring customer pvcs
> at all"
>
> He justifies his position with some tcp download tests of the pvc set for
> the proper (telco provisioned) line rate, and then comparing it to tcp
> download tests with the pvc set to ubr 45mbps, and seeing "no difference".
>
> I suspect this is a bad idea, but I would like an ATM expert's input on this.

You'd better find out whether the telco provider enforces VC bit rates. 
If it does and you send data higher than the provisioned ubr you'll 
actually see higher loss and reduced throughput than if you specified the 
ubr on your end.

You may not notice a difference now if there is only one active VC on the 
entire circuit but the moment you have a multiple active VCs and the 
aggregate ubr for those VCs approaches the line rate, I suspect you'll 
start to see throughput issues.