Finally:
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
and so just to be clear if they are not useful for e2e signaling what is
the purpose of advertising them for this purpose ?
Comments like these just knock me off. I always believe that any type of
advertising is being done for the purpose of routing and path computation
but have zero relevance for signaling. Am I not right ? Consider, for
instance, the case when all EROs are fully specified by the user. Can I
signal such LSP? If yes, do I need TED in this case?
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 5:33 PM
Subject: Re: I-D ACTION:draft-ayyangar-ccamp-lsp-stitching-00.txt
igor - see in-line:
[snip]
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
exactly - there is no *LSP stitching* anymore - we discuss about control
plane operations (the intermediate segment is an entity owned by the
control plane)
note: by the way, operation you are referring to is supported today
(without the procedures described as part of this document because this
has nothing to do with stitching)
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
well i think we should then determine the working assumptions here,
intermediate nodes part of an LSP segment are GMPLS nodes as any other,
otherwise the segment could itself not be setup (stitching is just a way
to leave control to the head-end of the segment but there are no
specific assumptions made in terms of signaling capabilities for the
intermediate nodes, they are assumed to be GMPLS signaling capable nodes
as any other)
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
and so just to be clear if they are not useful for e2e signaling what is
the purpose of advertising them for this purpose ?
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
not sure to catch your point, if you think a p2p LSP establishment may
fail not sure it is wise to start thinking about p2mp LSP establishment
- on the other side pre-provisioning of the segment if not guaranteed
within certain limits can not guarantee that you would be able to stitch
it afterwards (refresh, etc.)
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;
this may be the case but once known explicit label control on each link
is enough to assume continuity
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.
PCE, again PCE, but the computation of such path was possible well
before even the term did exist - you mix the computation with the access
to the computation result -
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.
it is the term "pre-provision" that causes the main issue here, one
dimension of the problem is simplified but how many are getting
complexified ? and where is the evaluation of this trade-off ?
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
.
.
.
.
.
.