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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
>