[c-nsp] ATM and ABR (DSL termination)

[Charles Sprickman]

Hi,

I'm stuck in a situation where we have a full ATM backhaul.  The order for 
our next DS3 is stalled.  In the meantime I'd like to give SDSL customers 
a better shot at getting their money's worth...

Speaking with our Covad rep he mentioned that I should look at setting up 
ABR "shaping" on all of our PVCs.  This brings up a few questions that I'd 
like to run by you folks before I turn this loose anywhere:

-It's my guess that this will not impact router CPU since I seem to 
remember reading somewhere that all the ATM level shaping/policing happens 
within the ATM card itself.  Is this correct?

-Am I reading the syntax of the abr command correctly?  For SDSL I'd like 
to set both PCR and MCR at 1500Kb/s (the max speed we sell) and for ADSL 
I'd like to set PCR to 3000Kb/s, MCR to 800Kb/s.  So on 12.2T this should 
look like:

sdsl: router(config-vc-class)#abr 1500 1500 1500 1500

adsl: router(config-vc-class)#abr 3000 800 1500 400

I'm not too worried about the input rates, since those should already be 
throttled by our carrier, but I'll set them anyhow...

Here's a snippet of the config prompts.  I'm hoping there's no 
mis-labelling here as the docs don't quite match what I get at the CLI:

router(config-vc-class)#abr ?
   <1-45000>     Peak Cell Rate(PCR) in Kbps
   rate-factors  Specify rate increase and rate decrease factors (inverse)

("rate-factors" is not mentioned in 12.2 or 12.2T docs)

router(config-vc-class)#abr 1500 ?
   <0-1500>  Minimum Cell Rate(MCR) in Kbps

router(config-vc-class)#abr 3000 800 ?
   <1-45000>  Input Peak Cell Rate(PCR) in Kbps
   <cr>

router(config-vc-class)#abr 3000 800 1500 ?
   <0-1500>  Input Minimum Guaranteed Cell Rate(MCR) in Kbps
   <cr>

Any feedback is appreciated.  From what I've seen at other ISPs people 
don't tend to fiddle with this stuff on DSL termination even though it 
looks like it could be quite handy when one is in a crunch or if one just 
wants to make sure the biz clients get a better guarantee...

Thanks,

Charles

--
Charles Sprickman
spork at inch.com