RE: More comments/questions on DS-TE solution draft

[Francois Le Faucheur <flefauch@cisco.com>]

Venkata,

At 12:36 17/02/2002 -0500, Naidu, Venkata wrote:
>Francois:
>
>-> >Another unrelated question: As far I understand, the
>-> >available bandwidth will get advertised periodically.
>-> >Do you think this approach will be sufficient for a
>-> >DS-TE network, with lot of LSPs being created and
>-> >deleted?
>->
>-> Available bandwidth are certainly advertised periodically.
>-> But they can
>-> also be advertised on various triggers. There has been lots
>-> of useful work
>-> done in teh context of PNNI in particular about what are teh
>-> godd triggers
>-> and the benefits that this extra advertisement offer.
>-> Yes, I think combination of periodic and triggered advertisement of
>-> available bandwidth will be sufficient for DSTE as it is
>-> today with regular TE.
>
>    But this periodic advertisements are based on some
>    thresholds (either configurable on per router/interface basis).
>    I didn't see any interoperable thresholds defined in
>    TE drafts. If routers are configured with different threshold
>    values (in between 5% to 10%) then there might be some
>    path setup problems in multi-vendor networks (I can think off)
>
>    One more concern is - "Network/Resource re-optimization". RFC2702
>    Section 5.6.4 Adaptivity Attribute - clearly specifies
>    requirements to do re-optimization. But *when and what* to
>    re-optimize is left as a local decision. I can think of many
>    example scenarios where to re-optimize resources. But I don't
>    know the implications in the multi-vendor networks.
>
>    Though not related to present discussion, there are just
>    some concerns lurking in my mind for long...

Right, those are really not DS-TE questions. There are more like questions 
about using a Link State for path computation. They are equally applicable 
to TE, DSTE and PNNI.

On the first point, I don't see an issue if routers are configured with 
different thresholds (or even if they were to implement different threshold 
mechanisms like one having 5 thresholds and the other 10 thresholds). It 
seems quite fine to handle that as a local matter outside standardisation. 
You may just end up doing more or less acurate path computation  (and have 
lower/higher CAC rejection rate) depending on actual link thresholding, but 
that's all. Also, I am not aware of any issues on that front raised in 
production networks using multi-vendor TE implementations today.
Have you identified specific scenarios where this would be a problem?

On the second point, same thing really. This seems quite fine as a local 
matter. Can't think of scenarios where this is a problem . Can you?

Cheers

Francois

PS: I posted both the DS-TE Requirements and DS-TE Protocol drafts today so 
they should appear on the IETF server soon.

>
>Venkata Naidu
>
>
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Francois Le Faucheur
Development Engineer, IOS Layer 3 Services
Cisco Systems
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Email:                 flefauch@cisco.com
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