Hi Young,
Happy to see that we have the same point on my first question.
Regarding to the second question , I think I need to express it more clearly.
In the beginning of section 3.3, the draft provides the initiation operations
for the case of inter-domain LSP in HPCE architecture. The main idea of E2E
path computation is as per Steps 4 to 10 of section 4.6.2 of [RFC6805], where
C-PCEs are responsible for intra-domain path computation, and P-PCE is
correlating all the responses from C-PCEs and stitching them with the
inter-domain links together as one inter-domain path.
After getting the required inter-domain path, the P-PCE starts the inter-domain
LSP initiation operations, and the detailed procedures are as per step 2 to 7
of section 3.3 of this draft. The main idea is P-PCE send the PCInitiate
message to the Ingress C-PCE, and then the C-PCE propergates it to the Ingress
LSP(PCC).
After receiving the PCInitiate message, the Ingress LSR needs to set up the LSP
hop by hop in dataplane via LDP (RSVP or someone else). To do such operations,
I guess the Ingress PCC MUST know the detailed Hop information of the whole
inter-domain path.
In the HPCE architecture without any abstraction, these procedures make sense
because the P-PCE can get the detailed hop informaition from each C-PCE, and
send it via PCInitiate message to the Ingress LSP.
While, if there exists abstraction (like the border nodes level abstraction)
between P-PCE and C-PCE, the P-PCE may get only abstracted path information
from each C-PCE. Following the procedures mentioned above, the P-PCE will send
the abstracted path information to the Ingress C-PCE, and then to the Ingress
LSR. Even though C-PCE has the ability to translate the abstracted path
information to C-PCE(PNC) level, the Ingress LSR still cannot get the overall
Hop information, because it receives the PCInitiate message via ONLY Ingress
C-PCE(without help of any other C-PCEs).
So I think the proceduress described in the beginning of section 3.3 are not
applicable for the HPCE architecture where abstraction exists.
Section 3.1.1 describes a different mode named "Per Domain Stitched LSP", and I
think this mode is better for HPCE architecture.
Thanks,
Best Regards,
Wei Wang
发件人：Leeyoung <[email protected]>
发送时间：2016-08-20 03:22
主题：RE: [Pce] stateful-HPCE
收件人："weiw"<[email protected]>,"[email protected]"<[email protected]>
抄送："Jonathan.Hardwick"<[email protected]>
Hi Wei,
Thanks for your comment on Stateful H-PCE draft. Please see my comment on some
of your questions. Dhruv might also have his comments.
Best regards,
Young
From: weiw [mailto:[email protected]]
Sent: Friday, August 19, 2016 9:13 AM
To: Leeyoung; [email protected]
Cc: Jonathan.Hardwick
Subject: Re: [Pce] stateful-HPCE
Hi Young and PCE WG,
I am now implementing a ACTN control framework for transport networks, which is
a usecase for stateful HPCE. In the coding process, I find some problems about
this draft, as follows.
In the beginning of section 3, it states that "In the hierarchical PCE
architecture, a P-PCE maintains a domain topology map that contains the child
domains (seen as vertices in the topology) and their interconnections (links
in the topology. The P-PCE has no information about the content of the child
domains.)". I think it means that P-PCE only has some abstracted information
about physical network elements.
YOUNG>> Yes, when it says vertices in the topology, it implies that it is an
abstraction. We can make it more clear on this in the next revision.
According to the considerations above, I think the stateful related messages
(PCUpd, PCRpt, PCInitiate) and PCRep should be used in a different way between
P-PCE and C-PCE, because we need to do some abstraction processing on these
message to report the abstracted information so that P-PCE can match them to
the abstracted topology and TE information it has. For example, in the
condition where C-PCE only report the border nodes to its P-PCE, it also need
to report a abstracted path (whose RRO feild is composed of border nodes) to
its P-PCE. Also, in the perspective of security, it not reasonable for C-PCE to
forward the physical network specific information carried in PCRep and PCRpt
message to P-PCE without any abstraction processing. It is a kind of
information leaking in the condition where C-PCEs do not want to provide
detailed information about their physical networks to P-PCE.
YOUNG>> It is correct that the there is a level of difference between MPI and
SBI (in ACTN terms) as to how much details should be disclosed. But the basic
stateful (and stateless) PCEP messages will be applicable as is across PCE-PCC
(SBI) and P-PCE-C-PCE (MPI). The current PCEP messages/Objects/TLVs allow
expressing TE information (which is basically, nodes, links, b/w, etc.) in an
abstracted way. I think you are talking about how to abstract RRO of an LSP for
instance. You can use “loose hop” notion to hide internal details, simply
giving the source border node and the destination border node.
Consequently, I suggest to add one section to clarify the abstraction
processing requirment for the stateful related messages (PCUpd, PCRpt,
PCInitiate) and PCRep.
YOUNG>> This can be done.
If the abstraction processing is mandatory, there would be another problem, as
follows.
This draft provide two usecases for LSP initiation in stateful HPCE context, as
section 3.3. One can be concludes as "initiated by P-PCE", and the other "Per
Domain Stitched LSP".
For the first case, the P-PCE can choose an optimal abstracted E2E path
according to the Hierarchical End-to-End Path Computation Procedure in section
4.6.2 of [RFC6805]. While, the P-PCE cannot initiate a LSP by sending this
abstrated path info to the Ingress PCC via ingress C-PCE, becuse the ingress
PCC would be confused by the abstracted hop information. How to deal with this
case?
YOUNG>> P-PCE should know the border nodes domain networks when it computes an
E2E path across multiple domains. P-PCE would express the C-PCEs to create LSP
between a pair of border nodes (source and destination) for each domain. Do you
see any issue with this? Then each C-PCE will setup an LSP that connects the
border nodes. I don’t think C-PCE would be confused with this method.
The draft is OK for the second usecase, where each C-PCE is responsible for
initiating its own intra-domain LSP.
Thanks,
Wei Wang
发件人：Leeyoung <[email protected]>
发送时间：2016-07-21 23:58
主题：[Pce] stateful-HPCE
收件人："[email protected]"<[email protected]>
抄送：
Hi PCE WG,
https://datatracker.ietf.org/doc/draft-dhodylee-pce-stateful-hpce/
We’d like to solicit WG’s comment on this draft. As Dhruv presented today in
the PCE WG meeting, this draft does not add any new protocol work. It is
informational only and the co-authors believe this draft can move to the next
step.
Thanks in advance for your comments, suggestions, etc for this draft.
Young (on behalf of co-authors and contributors).
_______________________________________________
Pce mailing list
[email protected]
https://www.ietf.org/mailman/listinfo/pce
