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Re: I-D ACTION:draft-ayyangar-ccamp-lsp-stitching-00.txt
Dimitri,
See my comments in line.
Igor
----- Original Message -----
From: "dimitri papadimitriou" <dpapadimitriou@psg.com>
To: "Igor Bryskin" <ibryskin@movaz.com>
Cc: <dimitri.papadimitriou@alcatel.be>; "Arthi Ayyangar"
<arthi@juniper.net>; <ccamp@ops.ietf.org>
Sent: Thursday, February 17, 2005 3:55 PM
Subject: Re: I-D ACTION:draft-ayyangar-ccamp-lsp-stitching-00.txt
> igor,
>
> > For the second time you are saying that I don't see the issue that you
are
> > pointed out and this is beginning to annoy me.
> >
> > Your point/question is very simple, which is what does it give to
advertise
> > stitching segments as FAs, is that correct?
> >
> > My answers are very simple either:
> >
> > 1) How else are you going to use statically provisioned segments as part
of
> > dynamically provisioned end-to-end LSPs ?
>
> you ask a different question from the initial issue because advertize a
> TE link was possible today without using stitching, however this issue
> also depends what do you mean by statical provisioning ?
IB>> I have segments that are provisioned/owned by the management plane
>
> > 2) How else you can accomplish a transition strategy when some of the
nodes
> > that are going to be involved in end-to-end dynamically provisioned LSPs
do
> > not have proper signaling software?
>
> and i did ask what is the point in applying LSP segment signaling on
> segment that "do not have proper signaling software"
IB>> The point is that transit nodes of the segments do not participate and
hence do not have to support e2e signaling
> > The specific example is using LSRs that
> > do not support p2mp signaling as transit nodes in p2mp LSPs. Your point
> > about advertising of node capabilities is relevant only for routing -
the
> > PCE computing p2mp tree may take in consideration the advertised node
> > capabilities and assume that stitching segments may be created
dynamically
> > if needed.
>
> just to be clear the PCE discussion is completely outside of the present
> discussion - afaik the working group has (still) to provide requirements
> for the PCE wg -
IB>> Just to be clear. You mentioned the use of advertised node
capabilities. My point is that these advertisements are useful for path
computation but are of no use for e2e signaling
>
> > What if I don't want them to be dynamically created and rather
> > have them pre-provisioned to spead up the process of p2mp tunnel setup
and
> > decrease blocking probability?
>
> not sure that compared to the global complexity of computing the tree
> this is going to be a significant improvement, but if you have the
> possibility to determine the bandwidth on the corr. segments i don't see
> here how you decrease the blocking probability (afaik propagation of
> segment related information is equivalent to the corresponding links
> advertisement)
IB>> Dynamic establishment of the stitching segments may fail
> > 3) What if I want to attract certain LSPs to use pre-provisioned
segments
> > even if the overall cost of such LSPs would be higher than if they would
> > take paths computed without consideration of these segments, but it is
> > desirable for the LSPs to use the segments anyway. Exanple: the segments
are
> > provisioned to satisfy wavelength continuity constraint and I don't have
PCE
> > that can perform path computation with such contraint on path segments
> > between points of OEO.
>
> as said above it would desirable to leave PCE aspects outside of the
> picture, but this application is really interesting because on one side
> i thought we had the label set to solve this issue (note: that even if a
> path is pre-computed explicit label control can be used to provision the
> segment between converting points - don't PCEs for this)
IB>> First, this is just an example of the situation when I want
pre-provisioned segments to be used in e2e LSP provisioning.
Second, satisfying the wavelength continuity constraint takes much more
than just using the label set. You need to have:
a) information about all lambdas in all isles of transparency;
b) very complex PCE that is capable of computing optimal path(s) that use
the same wavelength on all links within each OEO-OEO segments satisfying all
other optical constraints.
It is much simpler to pre-provision such OEO-OEO segments and advertise them
as TE links, than a simple PCE would do the job.
Igor
> on the other hand is how much possible pre-provisioned segments - so
> overhead - are now going to be advertised if the traffic demand is
> unknown ? and on the other hand, if all traffic matrix is known
> beforehand is there any rationale to create these segments instead of
> directly provisioning
>
> it is interesting to see that you are populating this discussion with
> PCE application - i would be more in favor in leaving the possibility of
> advertising segments once a clear set is being identified rather than
> the other way around
>
> > Igor
> >
> >
> >
> >
> >
> > ----- Original Message -----
> > From: "dimitri papadimitriou" <dpapadimitriou@psg.com>
> > To: "Igor Bryskin" <ibryskin@movaz.com>
> > Cc: <dimitri.papadimitriou@alcatel.be>; "Arthi Ayyangar"
> > <arthi@juniper.net>; <ccamp@ops.ietf.org>
> > Sent: Thursday, February 17, 2005 1:19 PM
> > Subject: Re: I-D ACTION:draft-ayyangar-ccamp-lsp-stitching-00.txt
> >
> >
> >
> >>
> >>Igor Bryskin wrote:
> >>
> >>
> >>>dimitri, see in line.
> >>>
> >>>----- Original Message -----
> >>>From: "dimitri papadimitriou" <dpapadimitriou@psg.com>
> >>>To: "Igor Bryskin" <ibryskin@movaz.com>
> >>>Cc: <dimitri.papadimitriou@alcatel.be>; "Arthi Ayyangar"
> >>><arthi@juniper.net>; <ccamp@ops.ietf.org>
> >>>Sent: Thursday, February 17, 2005 11:40 AM
> >>>Subject: Re: I-D ACTION:draft-ayyangar-ccamp-lsp-stitching-00.txt
> >>>
> >>>
> >>>
> >>>
> >>>>igor - see in-line
> >>>>
> >>>>
> >>>>
> >>>>>>>>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.
> >>>>
> >>>>which flexibility are we expecting here, this "segment" can
accommodate
> >>>>exactly one incoming request -
> >>>
> >>>
> >>>IB>> Disagree - the segment could be a component link within a bundle.
> >
> > In
> >
> >>>this case stitching FA TE link may accomodate multiple LSPs
> >>>
> >>> additionally only nodes part of the same
> >>>
> >>>
> >>>>area can make use of this advertisement -
> >>>
> >>>
> >>>IB>> Who said that sticthing segments must necessarily terminate on
> >
> > domain
> >
> >>>borders? There could be multiple reasons why a network operator could
> >>>pre-provision (dynamically or statically) LSP segments inside his
> >
> > network
> >
> >>>and advertise them (as bundles or individually) as TE links to be used
> >
> > for
> >
> >>>specific TE purposes.
> >>
> >>it is exactly these purposes that i am looking for
> >>
> >>
> >>>so in fact what it would allow
> >>>
> >>>
> >>>>is the possibility to avoid creation of a segment if the edge node
> >>>>receiving the request re-orients its request to the head-end for this
> >>>>advertisement
> >>>> |
> >>>>example: ----------D----------
> >>>> | |
> >>>> - A ---- Segment 1 ---- B -
> >>>> | |
> >>>> ----------C----------
> >>>> |
> >>>>
> >>>>you would have a segment between A-B that could be reached from C (the
> >>>>node receiving the incoming request) decides to make use of this
segment
> >>>> to reach B (so you would have C-A-B) but if this was the best path
why
> >>>>not creating directly a segment C-A-B, instead of now having one
segment
> >>>>C-A, the pre-provisioned A-B and probably one on top of it C-A-B ?
> >>>
> >>>
> >>>IB>> See my comment above. I might want to use statically provisioned
> >>>segments. I might want to use nodes that do not have proper signaling
> >>>software.
> >>
> >>what does that mean "proper signaling software"
> >>
> >>
> >>>For instance, recall the discussions on P2MP and how we want use legacy
> >
> > LSRs
> >
> >>>to be part of P2MP tunnels
> >>
> >>but in this case there is a flag telling capabilities of the nodes in
> >>order to allow for dynamically trigger the segment
> >>
> >>
> >>>>in case of classical FA-LSP it makes sense to advertize the FA link
> >>>>because it represents a lower region LSP (with usually a given ratio
of
> >>>>unreserved bandwidth that makes worth advertizing the FA link) but in
> >>>>case of a segment i do have some difficulties to excatly see where
this
> >>>>flexibility would deliver ?
> >>>
> >>>
> >>>IB>> Again, if you imagine that several parallel sticthing segments are
> >>>advertised as as single FA, how it would be different from the
bandwidth
> >>>usage point of view compared to advertising lower layer FA ?
> >>
> >>issues are different - FAs are used in manner to preferentially attract
> >>over them because - i am still looking for the reason for attracting
> >>over a bundle
> >>
> >>
> >>>In fact it would be even more useful, because in case of lower layer FA
> >
> > you need also
> >
> >>>to advertise termination/adaptation capabilities, while in case of
> >
> > stitching
> >
> >>>FA no addaptation is required.
> >>
> >>by the way you don't seem to see the issue that i am pointing out, so
> >>probably there is a need to go in more detailed examples before drawing
> >>the above confusing conclusion
> >>
> >>
> >>>Igor
> >>>
> >>>
> >>>>thanks,
> >>>>- dimitri.
> >>>>
> >>>>
> >>>>
> >>>>>>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
> >>>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>>.
> >>>>>>>
> >>>>>>
> >>>>>.
> >>>>>
> >>>>
> >>>
> >>>.
> >>>
> >>
> >
> >
> > .
> >