Progressing BC Models was RE: Progressing MAR

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

Hello Jerry,

See embedded :

>> > I believe the conclusion of our long discussion on BC 
>> Model was that we
>> > agreed to specify RDM and MAM and to investigate further 
>> other models
>> > including MAR.
>> 
>> I don't see that conclusion written down anywhere.  In 
>> Atlanta, the WG debated 1 default  versus 2 default models, 
>> and no conclusion was reached.  As to what to specify in the 
>> way of BC models, that's the discussion we're having now on 
>> all 3 models, so no conclusion is yet reached.
>> 

Looking at the Atlanta minutes:

"
[Francois] Propose to document not only one model but rather to document
two
    models. Propose that these two documented models be RDM and MAM. 
...
Jerry recommended that the MA model be the default BC model and
    that the RD model be an optional BC model (should be used only
    when preemption is also used).  
Jerry also recommended that we
    continue to study possible extensions to MA, such as MAR, to
    improve performance.
...
[Waisum]: Draft is a comparison of MAM and RDM... Proposes to have MAM
as default model.
"

So my reading of this is that at least back then, while we disagreed on
which should be default vs optional, we actually all agreed on (i)
specifying both MAM and RDM and (ii) further investigating MAR. My
impression was that the group also agreed with this (or at the very
least noone raised any issue with this).

It sounds like one good objective for our SFO meeting would be to
establish/document such agreement on :
	- which BC Model we should specify right away, and 
	- (coming back to Dimitry's question) which goes as
Standards/Experimental/Informational

My proposal will be:
	- progress RDM right away in Standard Track
	- progress MAM right away in Standards Track
	- keep investigating MAM extensions like MAR, and based on
upcoming conclusions decide then how to proceed
(Standards/Experimental/Informational/no-specification).

>> Anyway, my views are as follows:
>> 
>> 1. progress MAM.
>> 
>> 2. hold off on progressing RDM until some major issues have 
>> been resolved:
>> a) further extensions/protections should be proposed to 
>> protect against poor performance when preemption is not used,
>> b) at a minimum, provide a warning that RDM may be 
>> 'hazardous to the health of your network if preemption not used',
>> c) provide pointers to and/or inclusion of performance analysis.
>> 
>> 3. continue the discussion on MAR toward a consensus.
>> 
>> There are service providers who do not use preemption, and 
>> have major concerns with RDM and its dependence on 
>> preemption to work well, that it can perform poorly when 
>> preemption is not enabled.  Our preference would be to use 
>> models not dependent on preemption (MAM or MAR).  There was 
>> much support on the list that a BC model should not require 
>> preemption to work well.  I think you should take that into 
>> account in RDM, and provide extensions to protect against same.

We have discussed the relative properties of RDM and MAM at length. This
is precisely why we evolved towards speciying both RDM and MAM (rather
than keep trying to come up with a single super model that works
perfectly in all cases).
Some SPs do find RDM trade-offs very attractive. I believe Raymond Zhang
from Infonet, for example, indicated so at the mike at some stage in
Atlanta (although it didn't make it in the minutes).
I am not suggesting everyone should use RDM; this is why MAM is also
progressed.

Incidently, perhaps mechanisms like
draft-meyer-mpls-soft-preemption-00.txt may also alleviate some of the
concerns associated with preemption.

Cheers

Francois