Re: [Pce] Whither Stateless PCE?

[<[e-mail]>]

Hello all,

IMHO the discussion must be split into is 2 different subjects:

1/ PCInit message could be seen as an independent message compared to 
other PCReq/PCRep, PCRpt and PCUp. Indeed, the PCE uses the PCInit 
message after a request that comes from another interface (e.g. a 
RestConf API) instead of PCReq that comes from the router itself through 
PCEP. In fact, when you configure a tunnel on the router, only the path 
computation part is requested to the PCE. Complements of tunnel 
configuration still remain in the router configuration. In case of 
PCInit, all information must be provided to the router. This could be 
for example the traffic steering. So, IMHO, it is normal that the PCInit 
message evolves through extensions different from the other PCEP 
messages, and in particular PCReq, as it is not triggered by the same 
entity, i.e. an external component instead the PCC router itself.

2/ But, this will not make PCReq message obsolete. Indeed, RFC5440 will 
continue to be mandatory for stateful both passive and active mode even 
if it needs clarification in the draft. Let me explain. In passive 
stateful, a PCReq/PCRep sequence is drawn in Figure 7 of the pce 
stateful draft prior to the PCRpt message Now, the ambiguity comes from 
the active stateful mode and figure 8. Why is the PCReq/PCRep sequence 
not mentioned? Of course the tunnel is delegated in this mode, but, the 
delegation object has been added as an extension to the PCReq message in 
the same draft. So, IMHO, at the creation of the tunnel, the draft must 
precise that a PCReq/PCRep exchange with delegation=1 must be used prior 
to the PCRpt to be coherent with RFC 5440 and passive stateful mode.

The problem occured during our evaluation of commercial products on 
which we made interoperability tests. Indeed we observed different 
behaviours that are due to the draft ambiguity and conduct to some 
interoperability issues. The different cases are as follow:
  - a/ - PCReq/PCRep exchange to obtain a valid ERO before the PCRpt message
  - b/ - PCReq message to obtain a valid ERO but with no reaction from 
the PCE which is not conform to RFC5440
  - c/ - PCRpt with empty ERO (looks strange. What is the meaning of an 
Empty ERO ? a loose path ? no path ? )/PCupd to get a valid path which 
overlaps with standard RFC5440 PCReq/PCRep.
  - d/ - PCRpt with empty ERO and no PCUpd leaving the tunnel down.

Thus, PCC/PCE that used PCRpt/PCupd messages for active stateful mode 
are incompatible with PCC/PCE that used standard PCReq/PCrep exchange. 
We could not mix both behaviours (PCC that use PCReq message with PCE 
that react to PCRpt with empty ERO and reciprocally). The problem occurs 
only at the creation of the tunnel. Once created and up the tunnel is 
reported and updated by means of PCRpt / PCupd messages correctly in all 
cases.

To summarize: PCInit message could leave independently from other 
messages. PCReq is the basis of PCE and is mandatory in all use cases 
included the active stateful mode, but this need to be clarify in the 
pce stateful draft.

Regards

Olivier

Le 07/04/2016 23:22, Aissaoui, Mustapha (Nokia - CA) a écrit :
>
> Hi Adrian,
>
> I raised in December 2014 the technical issue in 
> draft-ietf-pce-stateful-pce that a PCC must be able to convey the 
> original parameters (constraints) of the LSP path (Bandwidth, Metric, 
> and LSPA objects) using a PCReq message to a PCE and subsequently 
> delegate the LSP to PCE using the PCRpt message. Otherwise, when the 
> LSP is delegated to PCE only the operational values of these 
> parameters can be included in the PCRpt message. The latter means that 
> the PCE will update the path without knowing exactly the original 
> parameters.
>
> For me, PCReq/PCRep are an integral part of operating an LSP in 
> stateful mode.
>
> Here is the link to the archived thread:
>
> https://mailarchive.ietf.org/arch/search/?email_list=pce&so=-date&q=%22+Path+Computation+Request+in+Active+Stateful+PCE%22
>
> Regards,
>
> Mustapha.
>
> *From:*Pce [mailto:[e-mail]] *On Behalf Of *EXT Adrian Farrel
> *Sent:* Thursday, April 07, 2016 12:48 AM
> *To:* 'Dhruv Dhody'
> *Cc:* [e-mail]
> *Subject:* Re: [Pce] Whither Stateless PCE?
>
> I think you are probably right, Dhruv.
>
> But referencing the ways in which customers deploy may be a little 
> limiting.
>
> To say PCE is widely deployed (even after all these years) may be an 
> exaggeration.
>
> Although we do have some clues about what is currently being pushed 
> for deployment.
>
> I think you have mainly grasped my point, however. We need to 
> understand which extensions are definitely only needed in one mode or 
> another, and which should be done in all modes (either because they 
> are needed or because we don't know).
>
> OTOH, I suppose TLVs are just TLVs. Once you specified the TLV it is 
> not rocket science to include it in a message. In fact, it is probably 
> one line of text to include it and only a short paragraph to describe 
> additional processing in other modes once you have described how it is 
> used in one mode.
>
> Where does that leave us?
>
> Adrian
>
> *From:*[e-mail] <mailto:[e-mail]> 
> [mailto:[e-mail]] *On Behalf Of *Dhruv Dhody
> *Sent:* 06 April 2016 23:07
> *To:* Farrel Adrian
> *Cc:* [e-mail] <mailto:[e-mail]>
> *Subject:* Re: [Pce] Whither Stateless PCE?
>
> Hi Adrian,
>
> Even in the brave new world of Stateful PCE, PCReq and PCRep messages 
> do play a role in the passive stateful PCE mode. PCReq/PCRep also play 
> a crucial role in the inter-domain and inter-layer context in the new 
> proposal like stateful H-PCE.
>
> At the same time mandating that every extension (say SFC) must also be 
> specified in a stateless manner when no customer deploy in such a way, 
> might be overkill.
>
> Perhaps we need to look at it case by case!
>
> Dhruv
>
> On Wed, Apr 6, 2016 at 4:00 PM, Adrian Farrel <[e-mail] 
> <mailto:[e-mail]>> wrote:
>
> Once upon a time, in a working group far, far away, PCE was basically 
> stateless.
> PCE acted in response to questions asked by PCCs.
>
> These days, everyone is excited by stateful PCEs and there is a lot of
> initiation (of LSPs or of control of LSPs).
>
> In the jabber room during today's meeting Ravi noted that not a lot of 
> the new
> drafts (maybe none of them) talk about PCReq messages. This raises the 
> question
> in our minds as to whether stateless PCE is obsolete.
>
> If (and only if) this mode of PCE usage has gone out of fashion, we 
> *might*
> consider cleaning up the protocol and architecture so that we don't 
> need to make
> protocol extensions to PCReq and PCRep messages when we make extensions to
> PCInit messages.
>
> Thoughts?
>
> Adrian
>
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>
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