[c-nsp] atm ubr settings?

[Gert Doering]

Hi,

On Mon, Apr 03, 2006 at 05:48:26PM -0700, goemon at anime.net wrote:
> "we have 600 customers at site XYZ, all set to 45mbps, and nobody has 
> complained yet. therefore there is no problem setting everyone to 45mbps 
> always".

It very much depends on the ATM network in between, and the traffic pattern
of those customers.

Scenario 1: the moment one customer starts attracting 40 Mbit/s of traffic 
(like "being a bad guy on IRC and getting a DoS flood") *all* customers 
suffer, because the ATM bandwidth will be sucked up, just to have the DSLAM 
drop the excess packets.

If you do proper VC shaping, no bandwidth in the ATM cloud is wasted.


Scenario 2: your carrier might enforce VC peak cell rates to make sure 
that you're not wasting bandwidth in their ATM network, for stuff that
will get dropped at the DSLAM *anyway*.  If you don't shape on your end,
every time the customer will do a large download (or anything that could
exceed their bandwidth), you'll see cell loss due to policing, which will 
make the line quality REALLY bad.


Our ATM/DSL carriers enforce VC policing, so without shaping on our end,
performance would be horrible.  Seems that "on site XYZ", the carrier does
not do it - not *yet*, that is.  They might find out that it's a good idea.

gert
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Gert Doering - Munich, Germany                             gert at greenie.muc.de
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