Re: [PWE3] PWE3 new WG items? PW QoS

[Scott W Brim <sbrim at cisco.com>]

Peter: See at the bottom.

On Mon, Feb 23, 2004 04:12:48AM -0500, Busschbach, Peter B (Peter)
allegedly wrote:
> To be precise: I am advocating that RSVP is *one* cure for all these
> problems, with the nice property that it exists today. Of course we
> can define another solution to PW-splicing from scratch, but I think
> it is preferable to use an existing protocol.
> 
> Otherwise, I agree with you that we need to define the scope of the
> problem before we can decide on a solution.

On Mon, Feb 23, 2004 04:26:19AM -0500, Busschbach, Peter B (Peter)
allegedly wrote:
> Assume one wants to set up a multi-segment from A via B and C to D to
> carry ATM traffic. Suppose that the segment between B and C is set up
> independently from the other two segments. Then it is possible that B
> indicates to C that it accepts a maximum number of ATM cells per frame
> equal to N1. Subsequently, B could learn from A that A accepts a
> maximum number of ATM cells per frame equal to N2. If N2 is smaller
> than N1, there is a problem. B might have to repackage frames it
> receives from C to make sure it doesn't exceed N2 cells in the frames
> it forwards to A.
> 
> Based on this example, it seems obvious to me that B has to receive a
> PW setup message from A before it can forward it to C and C has to
> receive a setup message from B before it can forward it to D. In other
> words, there is a clear order.

I was thinking of a different part of the problem.  In the case you
describe, where some entity has the intention of setting up a path de
novo, your approach feels good, including the use of RSVP(+) for the
critical points on the path to discover what resources are available and
agree on what needs to be allocated.  However, there are variables,
including pre-existence of PSN tunnels and PWs (of various sorts, not
just LSPs), whether the originator intends stitching to be involved in
PW setup, how discovery is done, and so forth.  

Let's decompose the problem space a little more.

Have a good time in Seoul ... Scott

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