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

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

Dimitri,
see my comment in line.

Igor

----- Original Message ----- 
From: "dimitri papadimitriou" <dpapadimitriou@psg.com>
To: "Igor Bryskin" <ibryskin@movaz.com>
Cc: "Arthi Ayyangar" <arthi@juniper.net>;
<dimitri.papadimitriou@alcatel.be>; <ccamp@ops.ietf.org>
Sent: Thursday, February 17, 2005 8:47 AM
Subject: Re: I-D ACTION:draft-ayyangar-ccamp-lsp-stitching-00.txt


> igor - see in-line
>
> Igor Bryskin wrote:
>
> > 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.
>
> you don't understand the question, it is do we have to consider as
> default behavior that a pre-provisioned is to be "advertized"

IB>> My point was that I do not see any difference in this respect between
the sticthing FA-LSP (the same layer FA-LSP) and FA-LSP created in the lower
layer. Besides, what do you mean by the default behaviour? The fact whether
to advertise//remove FA TE link is a policy driven carefully thought through
decision, a dnagerous one that could potentially destabilize the network.
I'd say that the default behaviour is "NOT ADVERTISE" in either case.
>
> now beside the fact that there are techniques to do so what would be the
> purpose of it ? and what it the overhead that such advertisement would
> create - that can be of course decreased by bundling them -
>

IB>> The purpose is exactly the same as for any other FA-LSP - add
flexibility in a particular layer.
Igor

> thanks,
> - dimitri.
>
> >>>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
> >>
> >
> >
> >
> >
> > .
> >
>