If we had a flow label processing in the network without flow label
setup perhaps I would have agreed with you.

But if we accept that:

 a. the flow label has no semantics
 b. the flow label processing in the Network /depends directly on/is
controlled by/  the flow        setup in the Network devices (forwarding
engines)

then, preserving the meaning given by an application to a flow label
(keeping it as a constant or not) is a function that can be very well
undertaken by "b." (flow setup). That in fact makes the absolute
restriction that you are suggesting UNNECESSARY.  Furthermore, the
restriction has a detrimental effect on the subset of applications that
could take advantage of a changing value. Saying nothing about the flow
label mutability, or leaving it to the flow label processing and setup,
is a more inclusive, and positive architectural approach.

Alex 

Tony Hain wrote:
> 
> Muhammad Jaseemuddin wrote:
> >  I completely agree with you that unless we have a
> > signalling/flow-establishment mechanism we cannot really define the
> > flow-label usage in a meaninful way. Perhaps we should wait until new
> > NSIS sginalling might come-up with some usage and mechanism for this
> > bit-space.
> 
> But it is the responsibility of this group to restrict their domain of
> choices to things that make architectural sense. As I said in the last
> note to Margaret, the participants in the QoS WGs have consistently
> proven they don't understand the value of an end-to-end constant. If we
> don't point out that the DSCP is their mutable field to play with so
> leave the FL alone, we will end up with 2 random numbers and application
> developers will continue to ignore QoS because they have no means to
> express their intent that will be valid at all points in the path.
> 
> Tony
> 
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