Hello Ramon, all,
Thanks for your comment. I'm agree with you and I just try to reactivate
the debate too.
IMHO, if we want PCE do a good job, i.e. not only finding the shortest
path, but also the one which fit optimally the request we need first to
compute the AS path to know with which PCE I will collaborate. This AS
path is not necessary the shortest one or the one provide by BGP. For
such AS path Computation, PCE needs suitable information i.e. at least
TE of the peering point.
Exchange such information is more a routing space and a problem of flooding.
Now the question is: can we used existing protocol (IGP-TE are good
candidate) or do we modify PCEP for that purpose ?
Regards,
Olivier
Le 23/09/11 10:55, Ramon Casellas a écrit :
Dear Olivier, all
Please see inline
El 22/09/2011 18:22, Olivier Dugeon escribió:
IMHO, I think that it is missing something in the different proposal
to compute inter-domain tunnel. This is related to the TED. Indeed,
there is no proposal to collect suitable information that could help
the PCE (in BRPC or in H-PCE) to select (compute) the AS path, and so
select the better (regarding the request) peer PCE. Such information,
like TE of the peering point between two ASs, are mandatory if we
want to select alternate AS path than the one announced by BGP. If
such mandatory information are out of scope of PCE WG, I'm afraid
that, for me, their is no difference between the BRPC and H-PCE,
instead on how PCE are cooperate. The result will be the same in term
of path computation.
As you may know, the issue of TED management and, in particular, TED
management in the context of multi-domain path computation is raised
regularly (including myself!) and no consensus seems to be reached.
To some extent, I understand the (architectural and functional) idea
of keeping TED management somehow decoupled from the actual path
computation function, as it is done in the context of single domain
path computation, where the way the PCE obtains the TED is out of the
scope (and in some sense, orthogonal).
However, I believe that in some cases both functions (path computation
and TED management) are slightly coupled (border node identification,
endpoint localization and topology aggregation for domain sequence
selection, to name a few in which an IGP-based TED may not be
sufficient). For what is worth, an approach that we proposed in the
past (as well as other implementers) has been to use PCNtf with
embedded OSPF-TE LSUs / LSAs (or XML files or any other encoding) TED
"slices".
This approach -- completely non-standard -- can be used for both
wrapping and forwarding InterAS links [RFC5392] -- which, I agree with
you, seems relevant for a more efficient selection of the AS path and
would seem to address your requirement. This is briefly mentioned in
Fatai's and Dan's draft-zhang-pcep-hpce -- the same approach can be
used to wrap any other topological information. We did in a research
project, including "virtual links or nodes" for topology aggregation
(i.e. full-mesh) in H-PCE. In private communications I got the feeling
that this is somehow "frowned upon" ;) and that AS peering and
connectivity is managed at another (i.e. managed) level.
Is this make sense for the PCE WG and if yes, do you think it is
suitable to propose a draft for that purpose (we have some ideas for
that here) ?
I am not against such a proposal, since it is easier and simpler to
"stick to a common way of doing things", although it is difficult to
decide and I would understand the WG position against it, if it was
the case. Nonetheless I, for one, would be interested in hearing your
ideas :)
Thanks
Ramon
--
Orange
*Olivier Dugeon*
FT/NSM/RD/CORE/M2I/CRM
Senior research engineer, QoS and network control
Phone/Fax: +33 296 05 2880/1470
Mobile: +33 6 82 90 37 85
[email protected] <mailto:[email protected]>
France Telecom
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