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RE: IETF54- Informal discussion on BC Model for DS-TE

Dimitry,

Thanks very much for your input. It's a good way to kick start the discussion on BC models. My thoughts below:

At 13:38 12/07/2002 -0400, Dimitry Haskin wrote:

Francois,

Consider this posting as my input into the informal discussion that I will
no be able to attend.

The Russian Doll BC model is a  fine model in its own rights. However it may
not be suitable as the default BC model that is mandated for diff-serv
capable MPLS devices.  My concern is that, due the nested nature of its
bandwidth constraints, the RD model does not make much sense if preemption
of established LSPs is not used as a part of a given diff-serv deployment.
I don't follow you. Russian Dolls model does not "mandate" the use of preemption. It just uses it for what it has been specified for (ie bounce off LSPs when needed).

My impression is that it is just not possible to simultanesouly :
-(i) ensure bandwidth sharing (ie no bandwidth wastage)
-(ii) ensure bandwidth isolation (ie a CT cannot have some of its bandwidth taken by another CT)
-(iii) refuse to use preemption

I believe SPs have requirements for (i) and (ii) and don't have a problem with using preemption, which is an existing TE mechanism.
I believe the Russian Doll model is a very good way to achieve (i) and (ii). Yes it involves preemption to do so, but that is exactly why preemption was specified for (ie let some LSPs which arrive later bounce earlier LSPs).
More generally, as discussed in draft-lefaucheur-tewg-russian-dolls-00.txt, the Russian Dolls model appears as a very efficient way to address the most important SP requirements (using preemption where necessary).

I don't think it would make any sense to sacrifice (i) or (ii) just for the sake of not using preemption. Do you?

Cheers

Francois



The question really boils down to whether support of preemption is to be
required (at least in the IETF framework) from the diff-serv capable MPLS
devices. So far support of preemption was optional. Moreover, IMHO,
diff-serv can be deployed in quite satisfactory way without use of
preemption. Furthermore, preemption of established LSPs may not be even
desirable in some deployments.

Given that the RD BC model implicitly requires use of preemption for it to
work, the posted question should be explicitly addressed one way or another
before the RD model can be selected as the model that every diff-serv
capable LR must implement.

Thanks,
  Dimitry

> -----Original Message-----
> From: Francois Le Faucheur [mailto:flefauch@cisco.com]
> Sent: Friday, July 12, 2002 5:59 PM
> To: te-wg@ops.ietf.org
> Subject: IETF54- Informal discussion on BC Model for DS-TE
>
>
> Hello,
>
> TEWG will not meet in Yokohama/IETF54.
>
> I'd like to invite the people who will be in Yokohama and
> have thoughts on
> default Bandwidth Constraints model for DS-TE, to get
> together for a very
> informal discussion on that topic.
>
> Let's meet in the lobby of the main hotel at 17:30pm on Monday.
>
> See you there
>
> Francois
>
>