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Re: I-D ACTION:draft-ietf-ccamp-lsp-stitching-01.txt
Arthi,
----- Original Message -----
From: "Arthi Ayyangar" <arthi@juniper.net>
To: "Igor Bryskin" <ibryskin@movaz.com>
Cc: <i-d-announce@ietf.org>; <Internet-Drafts@ietf.org>;
<ccamp@ops.ietf.org>
Sent: Monday, July 18, 2005 2:51 PM
Subject: Re: I-D ACTION:draft-ietf-ccamp-lsp-stitching-01.txt
> Hi Igor,
>
> Please see inline.
>
> > 1. Why are saying that LSP Stitching is a private case of LSP Hierarchy?
>
> > there is more differences than similarities:
> > The differences are:
> > 1) In case of H-LSP there is a data plane adjacency, while in case of
S-LSP
> > there is none (as you correctly pointed out);
> > 2) In case of H-LSP there is an adaptation in data plane (label push/pop
for
> > PSC), while in case of S-LSP there is none - just simple
cross-connecting
> > ( label swap) as in case of two "native " e2e LSP adjacent segments ;
> > 3) H-LSP could be used by many e2e LSPs, while S-LSP could be used by
> > exactly one e2e LSP
> > 4) Signaling is different - there is no label negotiation in stitching
> > 5) H-LSP is used as a "true" data link, specifically there is a resource
> > allocation on the H-LSP edges, while in case of S-LSP there is none
> > 6) From MLN point of view, H-LSP is created in a server (lower) layer,
while
> > the S-LSP is created in the client (same as e2e LSP) layer.
> >
> > There are two similarities that I can think of:
> > 1) There is a signaling and possibly routing (see below) adjacencies
between
> > the ends;
> > 2) Both H-LSP and S-LSP could be advertised as separate TE links or as
TE
> > bundles
> >
> > I would recommend to dedicate a paragraph and enlist there similarities
and
> > differencies
> -------> Based on the discussions on the list over the last revision, the
> message that the authors received was that we do not want to go about such
> a lengthy discussion of similarities and differences (NOTE that the draft
> already does clearly highlight them where applicable). Instead we want
> this ID to simply explain how LSP stitching functions. In other words the
> idea was to make this ID a complete document by itself. But since it does
> borrow concepts from the LSP hierarchy ID, just state the concepts that
> are applicable or inapplicable.
IB>> I see a problem here. Since we do not have another draft providing the
tight definition of LSP stitching, it is not good enough to describe it in
some light narrative manner. In section 1 you are saying:
1. Introduction
LSP stitching is a special case of LSP hierarchy. In case of LSP
stitching, instead of an FA LSP, an "LSP segment" is created between
two GMPLS nodes ....
I don't think that "LSP stitching is a special case of LSP hierarchy". The
two mechanism have some remote IMO resemblance in control plane and have
nothing in common in the data plane. The biggest difference is that the
stitching happens within the same network layer and hence in sharp contrast
to LSP hierarchy does not require reconfigurations in lower (fat pipe)
layer(s). Just because of that the stitching could be much more attractive
mechanism for control plane. At least there will be no questions like " Who
is going to pay for unused bandwidth?"
Anyway, all I asked was for a small paragraph summarizing similarities and
differences of both planes. That IMO would help.
One more point. You use terms FAs and FA-LSPs everywhere in the draft. This
is confusing because what you really mean hear is Hierarchical LSPs (H-LSPs)
and TE links enabled by H-LSPs. As I mentioned earlier, there is no place
for these terms in your draft because it mostly concerns about TE
inter-domain scenarios, while [LSP-HIER] has a focus on a single domain and
strictly mandates the LSP to be advertised into the *same* domain to be
considered as FA-LSP
>
> > 2. Why are you saying that a TE Link based on S-LSP can be used for
exactly
> > one e2e LSP? Parallel S-LSPs could be advertised as a single TE link
> > (bundle, see above) and hence can accomadate several e2e LSPs.
> ----> Igor, the draft does talk about this Bundling case.
IB>> My problem here is with the statement from section 2:
"An LSP segment TE link SHOULD NOT admit more than one e2e LSP into
it. " You do describe the bundling, which contradicts the statement
above. It may accept as many e2e LSPs as it has component links
>
> > 3. You are saying that S-LSP does not have a routing peering. Actually,
in
> > this respect it is no different from H-LSP: if it is advertised as a TE
link
> > into the same TE domain that was used for S-LSP creation (unlikely IMO
> > scenario) than it does not require the routing adjacency (in other
words, it
> > is an FA according to LSP-HIER definition), otherwise, it IS NOT and FA
and
> > does require the direct routing peering in the domain it is advertised
to
> > make it useful as a TE link in this domain
> -----> I am sorry, but I am missing your point here completely. Are you
> saying that the statement "the end points of an LSP segment do not have a
> routing adjacency", is incorrect or are you saying that "this is
> obvious" ? It is unclear to me what exactly your argument is. Please
> clarify.
IB>> To be more clear I should say the following. If an LSP segment is
advertised into a different TE domain it SHOULD have a routing peering
between the ends in the domain it is advertised, otherwise, it could not be
used as a TE link in this domain. This is because generally speaking the
data plane connectivity does not guarantee control plane connectivity in the
domain the link is advertised, and in GMPLS a connection could not be used
as a TE link without control channel connecting nodes handling the link. The
same applies to hierarchical LSPs as well. The exception is LSP (stitching
or hierarchy) advertised into the same domain, in this case it is FA-LSP and
does not need direct routing peering to be used as a TE link.
Cheers,
Igor
>
> thanks,
> -arthi
>
> >
> > Cheers,
> > Igor
> >
> >
> >
> > ----- Original Message -----
> > From: <Internet-Drafts@ietf.org>
> > To: <i-d-announce@ietf.org>
> > Cc: <ccamp@ops.ietf.org>
> > Sent: Friday, July 15, 2005 3:50 PM
> > Subject: I-D ACTION:draft-ietf-ccamp-lsp-stitching-01.txt
> >
> >
> > > A New Internet-Draft is available from the on-line Internet-Drafts
> > directories.
> > > This draft is a work item of the Common Control and Measurement Plane
> > Working Group of the IETF.
> > >
> > > Title : Label Switched Path Stitching with Generalized MPLS Traffic
> > Engineering
> > > Author(s) : A. Ayyangar, J. Vasseur
> > > Filename : draft-ietf-ccamp-lsp-stitching-01.txt
> > > Pages : 19
> > > Date : 2005-7-15
> > >
> > > In certain scenarios, there may be a need to combine together two
> > > different Generalized Multi-Protocol Label Switching (GMPLS) Label
> > > Switched Paths (LSPs) such that in the data plane, a single end-to-
> > > end (e2e) LSP is achieved and all traffic from one LSP is switched
> > > onto the other LSP. We will refer to this as "LSP stitching".
This
> > > document covers cases where: a) the node performing the stitching
> > > does not require configuration of every LSP pair to be stitched
> > > together b) the node performing the stitching is not the egress of
> > > any of the LSPs c) LSP stitching not only results in an end-to-end
> > > LSP in the data plane, but there is also a corresponding end-to-end
> > > LSP (RSVP session) in the control plane. It might be possible to
> > > configure a GMPLS node to switch the traffic from an LSP for which
it
> > > is the egress, to another LSP for which it is the ingress, without
> > > requiring any signaling or routing extensions whatsoever,
completely
> > > transparent to other nodes. This will also result in LSP stitching
> > > in the data plane. However, this document does not cover this
> > > scenario of LSP stitching.
> > >
> > > A URL for this Internet-Draft is:
> > >
http://www.ietf.org/internet-drafts/draft-ietf-ccamp-lsp-stitching-01.txt
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