Re: MPLS Inter-area TE requirement draft

Jim,

At 07:05 PM 12/31/2003 -0800, Jim Boyle wrote:

>JP, so you state that both optimality and scalability are
>requirements, yet you acknowledge that there will be trade-offs.  I
>believe it is important to prioritize the requirements, so as to best
>guide the discussion on the solution.

A few comments:
- you seem to make the statement that optimal always means non scalable, 
something I disagree with. Of course, more optimal very likely means more 
expensive to compute, hence the trade-off I was referring to.
- moreover, the notion of scalability of a particular computation solution 
must be determined based upon specific criteria: implementation efficiency, 
frequency at which the computation is triggered, computation time, ...
- finally, the path computation solution can perfectly be determined on a 
per LSP basis: use an optimal path computation for a few TE LSP carrying 
very sensitive traffic, for other LSPs, a less optimal but cheaper 
computation might be perfectly acceptable.

JP.

>regards,
>
>Jim
>
>On Wed, 31 Dec 2003, Jean Philippe Vasseur wrote:
> >
> > This is a requirement draft, not a solution draft. The requirement to be
> > able to compute an optimal end to end path is clearly stated in the draft
> > indeed, since it turns out to be a requirement for several SPs. You seem to
> > draw the conclusion that scalability yields to optimality which is
> > absolutely not an assumption of this requirement draft. Moreover, such a
> > debate will obviously take place when discussing the solution in CCAMP,
> > here is a *requirement* draft.
> >
> > Note that the requirement for a scalable solution is clearly highlighted in
> > the present draft:
> >
> > 5.1.    Objectives to preserve IGP/RSVP scalability
> >
> > Being able to achieve the requirements listed in this document MUST be
> > performed while preserving the IGP scalability, which is of the utmost
> > importance. Hence, the set of mechanisms defined to meet those
> > requirements MUST not require IGP extra-load which could compromise the
> > IGP scalability. In particular, a solution satisfying those
> > requirements MUST require for the IGP to carry some unreasonable amount
> > of extra information and MUST not significantly increase the frequency
> > of IGP flooding. Likewise, the solution MUST also preserve the
> > scalability of RSVP TE ([RSVP-TE]). Moreover, the solution MUST
> > preserve the concept of IGP hierarchy (no TE link information flooded
> > across areas).
> >
>
><snip>
>
> > >Am I off here?  I'm interested to here some feedback from the members of
> > >the WG if they feel scalability or optimality is more crucial, or if it
> > >is widely felt that they may harmoniously coexist without trade-off.
> >
> > Do you know any solution without trade-off ? Obviously not ... but I guess
> > that the pros and cons of each solution addressing the requirements will be
> > discussed in the solution draft.
> >
> > Thanks.
> >
> > JP.
> >
> > >regards,
> > >
> > >Jim
> >