Re: I-D ACTION:draft-ayyangar-ccamp-lsp-stitching-00.txt

["Igor Bryskin" <ibryskin@movaz.com>]

Dimitri, Arthi,
See my comments in line.

Igor

----- Original Message ----- 
From: "Arthi Ayyangar" <arthi@juniper.net>
To: <dpapadimitriou@psg.com>; <dimitri.papadimitriou@alcatel.be>
Cc: <ccamp@ops.ietf.org>
Sent: Wednesday, February 16, 2005 9:08 PM
Subject: Re: I-D ACTION:draft-ayyangar-ccamp-lsp-stitching-00.txt


> Hi Dimitri,
>
> Please see my replies (AA--->) inline.
>
> > > ---------> An LSP segment may be created either by configuration or
due
> > > to arrival of an e2e LSP setup request itself. Similar to an FA, an
LSP
> > > segment may or may not be advertised as a TE link. But, if
pre-created, it
> > > could be advertised, in which case other nodes may compute a path over
it.
> > > Why would you want to or not want to advertise an FA ?
> >
> > i understand the point on pre-created <-> advertised but this knowledge
> > may be useful for nodes part of the same area (not for nodes external to
> > this area)
> AA -------> Absolutely ...this definitely cannot be advertised outside the
> area (domain). I think this has been explicitly mentioned.
>
> so in case a node for inst. advertises three terminating
> > links with PSC-2 (one of these being the LSP segment) then a another
> > node (part of the same area) receiving an incoming multi-area PSC-2 LSP
> > request may start making use of this segment to join the next border,
> > therefore advertisement of the LSP segment may create a multi-hop
> > condition, but now once used relevance of the existence of the segment
> > is not a useful information (for the area) as there is no possibility to
> > make re-use of it except when the end-to-end LSP is torn down
> AA----------> I understand your point that once an LSP has been admitted
> into an LSP segment it is no longer usable by other nodes in that area.
> But would you rather stop advertising the link at this point, if you were
> previously advertising it ? Don't you think that is a big hammer ? E.g.
> how would a head end which has indeed computed a path over that LSP
> segment differentiate this event from an LSP segment down event where the
> link is deleted from the database ? So, all the document says today is
> that you set the unreserved bw on the LSP segment to zero. The idea is to
> still let other nodes know that the link exists but is unusable. It is
> not different from a FA-LSP being consumed...in that case we don't stop
> advertising the FA (if we were doing so previously), right ?
>

IB>> Completley agree with Arthi. Besides, several parallel stitching
segments could be advertised as a single bundle - hence, using the
advertised link by one LSP does not necessarily take away all link's
bandwidth.


> > a more technical point is related to the definition of an FA LSP which
> > per LSP-Hierarchy mandates crossing LSP region border: the head-end and
> > tail-end switching capability represent the SC of the resulting TE link
> > while intermediate node terminates the SC corr. to the switching type of
> > the FA-LSP (e.g. creation of a [PSC-1,PSC-1] link throughout a PSC-2
> > capable network with first and last link being [PSC-1,PSC-2] and
> > [PSC-2,PSC-1], resp.), while in the LSP segment case we would have now
> > the creation of a [PSC-1,PSC-1] link with first and last link being
> > [PSC-1,PSC-1] and [PSC-1,PSC-1], resp. so there is no region border
> > crossing anymore - so here the question is about definition and
> > detailing the triggers
> AA--------> As far as trigger for setting up an LSP segment is concerned,
> I agree that there is no longer the notion of "crossing region
> boundaries". I realize that the document doesn't discuss this, especially
> given that we are doing other comparisons with FA LSPs. So, I will add
> this discussion in the next revision. I think in case of LSP segment the
> trigger for LSP segment setup would come from a) successful switching type
> and switching capability match and b) some local policy on the node which
> dictates the setting up of an LSP segment.
>

IB>> I have a comment here. LSP-Hierarchy is not a Bible and could be
challenged in many ways. FA LSP is, generally speaking, created on a layer
boundary rather than on region boundary: nothing prevents creating a VC4 FA
LSP that starts and stops in the middle of TDM region to carry several VC12
LSPs. Furthermore, stitching FA is a special case of FA when it is used by
LSPs of the same layer as one where the FA-LSP was created. As for triggers,
there could be multiple ones for setting up/tearing down stitching FA-LSPs:
configuration, receiving setup request for inter-domain LSP, other policies.

Igor



> More on a) later.
>
> thanks,
> -arthi
>