Tony,
[lots deleted since I think the nub of our mutual misunderstanding is
in this bit]
> > Which QOS model? We have two, and they are different and require
> > different flow label semantics to work.
> >
> I fail to understand how either would break if they simply intrepret the
> flow label semantics as 'the source has identified this set of packtes
> as related'. In either case there is an out-of-band mechansim to
> translate the value to a router task.
But in the diffserv case, which is stateless (no signalling, no soft state)
the only out-of-band mechanism that works is if the flow label has
intrinsic semantics. The fact that the packet belongs to a class is
useless information on its own; you need to know what that class means,
and that can only be conveyed by an encoded field, since there is no
signalling or state.
> The place you appear to be
> struggling is finding a standard mapping between a psuedo random value
> and the Traffic Class field.
Yes, because it's impossible.
> Since the Traffic Class field is itself
> a non-standard value (and effectivly psuedo random from an end-to-end
> perspective) this seems pointless.
No, it's the whole point: the classifier at a domain ingress must
choose an appropriate DSCP value to write into the TC field, and that
*requires* the classifier to interpret the semantics of some set of
fields in the packet header.
>
>
> > > while the fact
> > > that there is no single definition of QoS across
> > administrative domains
> > > means that it is impossible to use any single set of bits to create
> > > that definition.
> >
> > See RFC 3140.
> >
> >From the above:
> In a given network domain, there is a locally defined mapping between
> DSCP values and PHBs.
>
> Therefore my statement stands, there is no single definition of QoS
> across administrative domains.
Indeed. The problem to be solved is choosing the most appropriate PHB and
DSCP for the given domain. The proposed solution is to use the globally
defined PHB ID to drive the classifier.
Brian
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