Subject: [Pce] 答复: Re: 答复: Re: 答复: Re: New I-D : draft-wang-pce-inter-as-extentions-00.txt

From: [email-masked]
Date: Fri, 1 Apr 2011 17:36:35 +0800

Dear JP, 

As described in BRPC(RFC5441): “in the case of inter-AS TE LSP 
computation, this also requires adding the inter-AS TE links that connect 
the domain(i) to the domain(i+1).”
Though RFC5392 introduce a proxy method: “The ASBR will normally generate 
an LSA describing its own side of a link; here we have it 'proxy' for the 
ASBR at the edge of the other AS and generate an additional LSA that 
describes that device's 'view' of the link.”, but for bidirectional LSP , 
I think it is not clear how to use BRPC to compute an inter-AS 
bidirectional path.

Considering the following Scenario of inter-AS bidirectional LSP 
computation from R1 to R13:

In our draft, we think that PCE3 should compute bidirectional LSP from 
every entry BN to R13,and PCE3 should tell PCE2 all of the unidirectional 
inter-as links that satisfy the constraints（for the entry node R9,it may 
be connect to more than one exit BN of AS2,and PCE3 doesn’t know which 
link in the reverse direction will satisfy the constraints）.
As method 1 described in our draft, we can use ERO to carry the inter-as 
paths, but there may be some duplicated information:
Path R9 to R13 is the same, but there are two nodes（R7、R8） from R9 to 
AS2，so the path represented as R7\R9\R11\R13, R8\R9\R11\R13.
So we think maybe it’s better to use a new object to carry the inter-as 
links.

For the BRPC, PCE2 in AS2 should compute path from every exit node(R7、R8) 
to the R13 at first,then compute from R5、R6 to R13.

So there are two options for the next step.
Adding the above procedure into rfc5441.
Introduce another draft as we proposed to resolve this problem without any 
proxy.

What is your suggestion?

Best Regards, 

Xuerong Wang 

JP Vasseur <[email-masked]> 
2011-03-29 15:54

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Re: [Pce] 答复: Re:  答复: Re:  New I-D : 
draft-wang-pce-inter-as-extentions-00.txt

I have a different read, but let's discuss ... and listen what the WG 
thinks.

On Mar 29, 2011, at 9:25 AM, [email-masked] wrote:

Hi, 
We need to extend PCEP as well as BRPC. 

With extending PCEP to distinguish and being compatible with the BRPC 
procedure defined in RFC5441, we introduce a new flag to indicate that the 
Inter-AS links which satisfy the congstraints must be carried in PCRep. 
We may carry the inter-as links in two ways,use ERO or define a new 
object(i.e. CRO in the draft). 

There may be less extensions by using ERO to carry the inter-AS links, but 
this method will also carry some repeated information. 

<Mail Attachment.gif> 
For example, there are more than one inter-AS links from R9 to AS2, and we 
assume that 
all the inter-AS links satisfy the constraints. 
VSPT computed by PCE3  is extended to include Inter-AS link from AS3 to 
AS2, some duplicated information as shown follwing:
  
<Mail Attachment.gif> 
If we define a new object,that will be more efficent: 
<Mail Attachment.gif> 

Besides of that,BRPC procedure will be extended to include follwing steps 
in red colour: 
<Mail Attachment.gif> 

<Mail Attachment.gif> 

Best Regards, 

Xuerong Wang 

JP Vasseur <[email-masked]> 
2011-03-29 13:40 

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Re: [Pce] 答复: Re:  New I-D : draft-wang-pce-inter-as-extentions-00.txt

Hi, 

On Mar 28, 2011, at 4:33 PM, <[email-masked]> <
[email-masked]> wrote: 

Dear JP, 
There maybe several inter-AS links between two adjacent ASes, so we just 
selected some of them that can satisfy the constraints in both of the 
directions. Of cause, if all of the inter-as links can not satisfy the 
constraints, PCE will stop relying as you say,and will reply an PCRep 

  message including a NO-PATH object. 
 
Thanks for your questions 

Thanks for your reply - this s understood but precisely my point: why 
would you need 
protocol extensions ? 

thanks. 

JP. 

Xuerong 

JP Vasseur <[email-masked]> 
2011-03-28 16:47 

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Re: [Pce] New I-D : draft-wang-pce-inter-as-extentions-00.txt

Dear Authors, 

Thanks for your document. Quick question: when relaying the PCReq, why not 
simply 
check the TED in the reverse direction and stop relying if constraints are 
not satisfied ? 

Thanks. 

JP. 

On Mar 14, 2011, at 2:45 AM, [email-masked] wrote: 

Dear all,  
We have uploaded a draft, which is about  extensions of Backward-Recursive 
PCE-Based Computation (BRPC) to support bidirectional  inter-AS LSP path 
computation. 

I think it is important  to get bidirectional Inter-AS TE link information 
for inter-AS  path  computation. 

If you are interested in this topic, hope you can have a look and review 
this draft. 
URL : http://www.ietf.org/id/draft-wang-pce-inter-as-extentions-00.txt 

We would like to appreciate your comments and suggestions. 

Thanks
Xuerong

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