RE: Moving right along ... Switching Type

[John Drake <jdrake@calient.net>]

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