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

Neil,

At 16:38 15/07/2002 +0100, neil.2.harrison@bt.com wrote:

Francois,

Your comments seem OK to me.......but I have to point out that my
observation on pre-emption was quite general (so not just this DS/TE case,
and it can also apply to other network technologies like ATM or even SDH
VCs).  I am not so concerned for cases where traffic that gets dropped stays
dropped (which is similar to the 1:1/N protection switching case when 'extra
traffic' which is using the protection path gets dropped when the 'working'
traffic path fails), but rather where multiple priorities exist and one get
get a knock-on effect of 'bumped' traffic subsequently 'bumping' lower
priority traffic (and so on).
Thanks. Makes sense to me.

Let me reclarify that
- the Russian Dolls model does not "mandate" preemption. It can certainly be used without preemption.
- when used without preemption, it works reasonably well , but not perfectly. ie it achieves bandwidth efficiency and avoids QoS degradation. but it cannot provide complete isolation.

Now, the MAM model, can also work without preemption. When used without preemption, it can provide isolation, but this is at the cost of very large inefficiencies.

Where I am getting at is that while it MUST be possible to disable preemption and the model should still work reasonably well without preemption, there are other goals which are kind of pushing towards use of preemption . So, in the specific context of selection of a Default BC Model for DS-TE, we must keep it mind that the exercise is all about picking a good compromise (must work without preemption, but may have to involve preemption to achieve some particular combination of goals).

Unless, of course, we identify some new model which can do everything simultaneously, but this is not documented yet.

Cheers

Francois



regards, Neil

> -----Original Message-----
> From: Francois Le Faucheur [mailto:flefauch@cisco.com]
> Sent: 15 July 2002 15:22
> To: neil.2.harrison@bt.com
> Cc: te-wg@ops.ietf.org
> Subject: RE: IETF54- Informal discussion on BC Model for DS-TE
>
>
> Neil and all,
>
> At 10:47 15/07/2002 +0100, neil.2.harrison@bt.com wrote:
> >I'd agree with this too......our experience of pre-emption
> schemes in other
> >technologies tells us we would want to be able to disable them.
>
> So we're hearing:
>          -i- it should be possible to disable preemption
>          -ii- when preemption is disabled, the Model should
> still work
> reasonably well.
> Fair enough.
>
> I also understand that:
>          -iii- there should be effective use of bandwidth (ie good
> bandwidth sharing among CTs).
>          -iv- there should be some isolation (ie a CT cannot
> hogg the bw of
> another CT).
>          -v- there should be protection against QoS
> degradation (at least
> of the premium CTs e.g Voice, Premium DAta...).
>          -vi- the BC model should be reasoanly simple and
> shouldn't require
> additional IGP extensions.
> Is this right, or are any of those actually non-goals?
>
> Thanks
>
> Francois
>
>
> >regards, Neil
> >
> > > -----Original Message-----
> > > From: Geib, Ruediger [mailto:Ruediger.Geib@t-systems.com]
> > > Sent: 15 July 2002 08:21
> > > To: gash@att.com
> > > Cc: te-wg@ops.ietf.org
> > > Subject: RE: IETF54- Informal discussion on BC Model for DS-TE
> > >
> > >
> > > Hi Jerry
> > >
> > > > > 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.
> > >
> > > > Not all SPs assume the use of preemption.  So the default BC
> > > > model should not assume ('require') the use of preemption to
> > > > operate efficiently.
> > >
> > > Yes, that's correct. I'd prefer a default BC model where
> > > preemption is an optional add on instead of a mandatory feature.
> > >
> > > Regards, Rüdiger
> > >
> > >
> > >
>
>
> _________________________________________________________
> Francois Le Faucheur
> Development Engineer, IOS Layer 3 Services
> Cisco Systems
> Office Phone:          +33 4 97 23 26 19
> Mobile :               +33 6 19 98 50 90
> Fax:                   +33 4 97 23 26 26
> Email:                 flefauch@cisco.com
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