Michael Thomas wrote:
>
> Brian E Carpenter writes:
> > Excellent summary. We originally chose a 6 bit diffserv field partly because
> > it was available in both IPv4 and IPv6, and partly because it allows for
> > very efficient classification in *core* routers, with the more demanding
> > multi-field classification being left to border routers.
> >
> > The question before the house (in the end that means both ipng and diffserv)
> > is whether the added complexity of adding the flow label to the diffserv
> > model is justified by the gain in expressiveness. It doesn't do anything
> > for the trust model.
>
> I haven't heard about any imminent shortage of DSCP's.
> Indeed, it seems that there's only a small handful
> (2-6) that I've ever heard people contemplating. Maybe
> I just don't travel in the right circles...
We have deliberately been *very* conservative about defining standard PHBs, since
we want to be very sure about what we standardise. But there are a potentially
infinite number of local-use PHBs. That is why the DSCP value is mappable, and why
the PHB ID was defined, so that local-use PHBs can be registered with IANA and
signalled. The idea here is to stretch the semantics of the PHB ID just a little.
Normal semantics of a PHB ID:
"This is local-use PHB number 379"
Stretched semantics:
"This is local-use PHB number 379 and according to our SLA, that gets classified
as real-time traffic needing at least a 10 Mbit/s rate"
Brian
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