> > There are no stupid questions. Some of the pushback is
> > simply based on the fact that the diffserv model of QoS
> > is inherently broken because there is no end-to-end
> > immutable set of bits for local decisions to be based on.
>
> This is a very unfair comment. Diffserv is just fine in the
> case of unencrypted traffic. It has a problem (and so does
> intserv I suspect) with tunnel or transport mode ESP.
ESP is just one of the cases in which "looking at the port numbers" does
not provide sufficient information to make an informed decision. There
are many examples that do not involve ESP, e.g. an audio stream can
carry different levels of hierarchical encoding on successive ports, an
HTTP transaction can carry a medical transaction just as well as
recreational content, a file transfer may be a virus update or a virus
propagation. At some point, the classification decision has to rely on
information provided by the source.
In fact, there is no contradiction between the "immutable" requirement
that Tony is advocating and Brian's "diffserv handle" requirement. In
the diffserv model, the actual classification is based on the 6
classifier bits; there is no context that this can be mutable, since
ISPs must be authorized to reclassify traffic. The reclassification is
based on information carried in the packet, part of which is the label
affixed by the source; making that label immutable is a good thing,
since it prevents intermediaries from removing the information that can
be used by a downstream router.
-- Christian Huitema
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