Brian E Carpenter <[EMAIL PROTECTED]> wrote on 11/14/2006 11:36:40 AM:
> ...
>
> This illustrates some of my concerns about this requirements work being
> done outside the IETF.
> ...
>
> 2. The notion that solutions such as precedence and preemption
> are (a) requirements and (b) applicable to all applications just
> doesn't compute for me. We'd actually need to understand at a more
> basic level what the functional requirements are, in terms that are
> meaningful for a datagram network. I don't believe that will
> happen in ATIS or ITU-T.
>
> Brian (personal opinion)
>
Exactly.
In the circuit switched world, a circuit is either up or down, and
"preemption" means taking the circuit down.
But in the IP world, there is a full continuum of states in between. Some
of these are candidates for a useful service, and some of which aren't.
The understanding of this continuum, and of the (intended and unintended)
consequences is much stronger in the IETF than in the
historically-circuit-switched world.
Some of the possibilities in that continuum include (in no particular
order):
- Allowing extra sessions in, and permitting degradation in QoS across all
sessions.
- Allowing a higher packet drop rate across all the "lower priority" calls.
- Negotiating a lower bandwidth allocation, possibly accompanied by a
changing to a lower rate bandwidth codec when a higher priority session
needs to "preempt".
- Negotiating (or arbitrarily imposing) a different PHB (e.g. AF or BE
rather than EF) for lower priority sessions when a higher priority session
needs to "preempt".
- Different Capacity Admission Control mechanisms for different priority
sessions.
The analysis/understanding of these (and other) alternatives is much better
done in the IETF than in the historically-circuit-swiched SDOs.
Janet
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