Re: [Dart] AF - DSCPs, PHBs and remarking

["Bless, Roland (TM)" <[e-mail]>]

Hi Ruediger,

Am 17.06.2014 09:52, schrieb [e-mail]:
> you are of course correct with your assessment on standards. You've asked 
> for information on what's implemented today and that's what I've provided.
> 
> Each AF DSCP identifies an individual PHB. If classification is DSCP 
> based and limits apply on the number of PHBs, that's what providers have 
> to respect. This limit still applies, if e.g. all AF4 packets are operated 
> by the same scheduler (which I'd expect from a provider deployment).

Each AF class (2 or 3 PHBs) usually only needs a single queue.
It is not allowed to map an AF class to only a single PHB:
   Within each AF class, a DS node MUST accept all three drop precedence
   codepoints and they MUST yield at least two different levels of loss
   probability.
So at least one needs to distinguish between AFx1 and AFx2/AFx3.

> It is also somewhat demanding to configure 14 PHBs to support just rtcweb 
> on a  retail access and then provide additional PHBs for services of a 
> provider. The provider may offer some services with admission control and 

If you want to realize all proposed mappings of
http://tools.ietf.org/html/draft-ietf-tsvwg-rtcweb-qos-00
you probably need 7 separate queues (LE, BE, AF1-AF4, EF)
and at most 15 DSCP to PHB mappings.

> if rtcweb isn't running through the same admission control, this requires 
> additional PHBs. Some carriers may have deployed DiffServ already, when 
> rtcweb starts to use it. 

I think that you'll need admission control for EF and AFx1 PHBs
otherwise you'll end up with best-effort behavior in overload
situations...

Regards,
 Roland