Re: Moving right along ... Switching Type

[Zhi-Wei Lin <zwlin@lucent.com>]

Hi John,

I think I've mentioned this before, but I'll repeat myself. I think 
switching capability may have be useful in identifying what is allowable 
for routing purposes and for discovery purposes.

But once those are identified, signaling does not need to get involved. 
You responded to Ben that the switching capability field is end-to-end 
and does not change in intermediate nodes. Is this right?

Zhi



John Drake wrote:

> Ben,
>  
> I think part of the problem is that you also need to read the GMPLS routing
> drafts:
>  
> http://search.ietf.org/internet-drafts/draft-ietf-ccamp-gmpls-routing-00.txt
>  
> There are also comments in your text.
>  
> Thanks,
>  
> John
> 
> -----Original Message-----
> From: Ben Mack-Crane [mailto:Ben.Mack-Crane@tellabs.com]
> Sent: Monday, October 29, 2001 9:53 AM
> To: Kireeti Kompella
> Cc: ccamp@ops.ietf.org
> Subject: Re: Moving right along ... Switching Type
> 
> 
> 
> In reviewing the GMPLS signaling drafts I have been unable to
> get a clear understanding of the need for and use of the Switching
> Type field in the Generalized Label Request object.
> 
> 
> JD:  The Switching Type field is for handling the situation where there
> are multiple switching capabilities per interface (see section 6.4.6 of
> draft-ietf-ccamp-gmpls-routing-00.txt)
> 
> 
> This appears to be an attempt to address LSP setup involving multiple
> layer networks, but it does not adequately address the issues involved.
> 
> 
> JD:  Would you please provide some additional prose explaining your
> reasoning on this?
> 
> 
> That it "Indicates the type of switching that should be performed on a
> particular link." makes it seem to be a local concern, while others
> have indicated it is an end-to-end field. For example, George Swallow
> says "It is my understanding that for a given LSP it does not change, 
> but is carried end-to-end and applies at all intermediate hops along 
> the path."
> 
> 
> JD:  I think George's interpretation is correct, and I don't think the
> other text you quoted contradicts George.  If a given TE link supports
> multiple switching types, the node controlling that link needs to know
> what switching type a given LSP wants to use.  
> 
> 
> As an end-to-end item I have trouble understanding how the originating node
> would determine how to set this (on what basis one determines what switching
> choice to make in all cases).  In fact, I'm not sure why the originating
> node would care what type of switching is used as long as the LSP is
> delivered
> to the egress faithfully.
> 
> 
> JD:  The orgin node uses the switching capability information in the link
> state
> database in its CSPF calculation to ensure that switching capability is
> consistent
> along the path of the LSP.  
> 
> 
> Regards,
> Ben Mack-Crane
> 
>