Re: [CCAMP] Objective function draft

[Gert Grammel <[e-mail]>]

Hi Julien,

Most of the discussions about UNI/ENNI are confusing. Let's start with the remark that UNI/ENNI are terms defined in G.709 and do not relate to layers. They are reference points. You can think to place them in the middle of the fiber between a router and a ROADM. Since it is just fiber, it is pretty clear that no layer crossing is happening there.
In IETF we have the overlay concept which also doesn't relate to layers but to an administrative domain. Hence an operator can choose to place a 'GMPLS-UNI' where he wants.
Admittedly common wisdom places UNI as inter-layer communication and here is where confusion starts. AFAIK the terms UNI-C and UNI-N as well as the notion of a 'UNI-protocol' have been brought up in OIF. For whatever it is or was, initial UNI was from SDH/SONET client to SDH/SONET server, hence again no layer crossing even at the protocol level.

If different layer switching is involved on both sides of an interface, the best reference is RFC5212 (requirements) and RFC6001. They define a consistent multi-layer switching and adaptation model.

So in order to stay inside a consistent terminology we decided to go strictly with IETF terminology. That's the best we can do for now. 

To your points:
- the routing task involves both the IGP and the signaling protocol, especially in case of loose hops or crankbacks;
--> what you mean with routing task? Is it the routing process itself or something more?

- the objective function only makes sense per LSP, which allows to consider it in LSP-related protocols (PCEP, RSVP-TE... as opposed to IGPs or LMP).
--> an objective function could make sense per LSP if routing information is insufficient. It starts with the assumption that a router down the road may be able to find a better path than what the ingress router does. Given that the ingress has no means to verify if the objective has been followed this may turn out to become a debugging nightmare.

Gert




-----Original Message-----
From: JP Vasseur (jvasseur) [mailto:[e-mail]] 
Sent: Tuesday, September 18, 2012 2:30 PM
To: Julien Meuric
Cc: Gert Grammel; [e-mail]
Subject: Re: [CCAMP] Objective function draft

I an completely sharing Julien's point of view. 

JP Vasseur
Cisco Fellow

Sent from my iPhone

On 18 sept. 2012, at 05:27, "Julien Meuric" <[e-mail]> wrote:

> Hi Gert.
> 
> As Daniele has just said, almost all the information in an inter-layer signaling can be seen as input/constraints to the routing process. The IGP-TE brings some link-state information to some network nodes so as to achieve path computation; the result is used in the signaling protocol, on a per LSP basis. I would said that:
> - the routing task involves both the IGP and the signaling protocol, 
> especially in case of loose hops or crankbacks;
> - the objective function only makes sense per LSP, which allows to consider it in LSP-related protocols (PCEP, RSVP-TE... as opposed to IGPs or LMP).
> 
> I feel that draft-beeram-ccamp-gmpls-_enni_ is clearly introducing some great confusion in the vocabulary: it is a superset of draft-beeram-ccamp-gmpls-_uni_-bcp while removing the pointer to the ITU-T reference point. A possible option is just to avoid those terms and stick to protocols, namely RSVP-TE and IGP-TE.
> 
> Regards,
> 
> Julien
> 
> 
> Le 17/09/2012 23:22, Gert Grammel a écrit :
>> Hi George,
>> 
>> The objective function is in the end a routing information. Mixing routing and signaling in one protocol is something I don't feel comfortable with.
>> 
>> In other words, if routing is needed between client and server, UNI 
>> is the wrong choice. ENNI should be considered instead and Draft-beeram-ccamp-gmpls-enni would be a good starting point.
>> 
>> 
>> Gert
>> 
>> 
>> 
>> ________________________________________
>> From: [e-mail] on behalf of George Swallow (swallow)
>> 
>> Hi Julien -
>> 
>> On 9/17/12 9:37 AM, "Julien Meuric" <[e-mail]> wrote:
>> 
>>> Hi George.
>>> 
>>> Sorry for the late response. You are right: the minutes are not 
>>> enough to trace the full discussion (which we also resumed right 
>>> after the meeting). Let us start by thanking Adrian (as AD? former PCE co-chair?
>>> author of... ;-) ) for bringing the PCE-associated vocabulary to a 
>>> common understanding.
>>> 
>>> Actually my concern is sustained by 2 points:
>>> 
>>> 1- The scope of the draft is about giving control of the routing 
>>> objective function to the client node facing a transport layer. I 
>>> see already several existing solution to achieve it:
>>> - a PCEP request from the signaling head node is an option (which is 
>>> associated to the advertisement of the supported objectives in 
>>> PCEP);
>>> - building IGP adjacencies between client and transport edge nodes 
>>> (a.k.a. "border model") is another one.
>>> In this context, it do not think extending RSVP-TE for this kind of 
>>> application is worth the effort, since the requirement can already 
>>> be addressed.
>> As I understand it, in the optical and OTN cases, the border model 
>> would not be popular as in many organizations this crosses political 
>> boundaries.
>> 
>> The point of the draft is to keep the UNI implementation simple and 
>> not require a PCEP on the uni-c or necessarily on the uni-n.  We will 
>> keep the format aligned so if the UNI-N needs to make a request of a 
>> PCS, it can do so rather simply.
>>> 2- There are cases when previous options are ruled out of a given 
>>> deployment. I do believe that it is not simply due to protocol 
>>> exclusion, but rather to the fact that the SP wants transport 
>>> routing decisions to remain entirely within the transport network 
>>> (in order to fully leave the routing policy in the hands of people 
>>> doing the layer dimensioning). Thus, I feel this trade-off in path 
>>> selection tuning is rather unlikely to happen and I fear we may be 
>>> talking about RSVP-TE over-engineering here.
>> The idea is simply to allow the client to express its needs/wishes.  
>> The UNI-N remains in control.  By policy it can use the objective 
>> function or not.  Further if it does use the objective function and 
>> fails to find a path it can either say that there was no path or it 
>> proceed to setup what it can.
>> 
>>> (That is also why I preferred to consider your I-Ds separately 
>>> during the CCAMP meeting.)
>> Agreed.  I will ask for separate slots.  The discussion at the end 
>> was rather disjointed.
>> 
>>> However, my comments are mostly related to the client/transport 
>>> relationship. If the I-D is extended to cover more use cases with 
>>> wider scopes (Adrian has made interesting suggestions), turning the 
>>> overlay interconnection into one among a longer list, then my 
>>> conclusion may be different.
>> I'm happy to widen the scope in this way.
>> 
>> ...George
>> 
>>> Regards,
>>> 
>>> Julien
>>> 
>>> 
>>> Le 11/09/2012 21:28, George Swallow (swallow) a écrit :
>>>> Julien -
>>>> 
>>>> Reading the CCAMP notes (which capture little of the actual
>>>> discussion) I see that there may have been a perception in the room 
>>>> that PCE functionality at the UNI-N was assumed (actual or proxy).
>>>> 
>>>> This is not the case. The reason for our draft is that with the 
>>>> UNI, much of the functionality that resides at the headend is moved 
>>>> to the UNI-N. So the UNI-C needs a way to express an objective 
>>>> function even if there is no PCE.
>>>> 
>>>> Operationally it seems burdensome to require a PCEP at the UNI-C 
>>>> and a PCEP at the UNI-N, when all that is being done is enabling 
>>>> the UNI-N to perform what the client would do if it were connected 
>>>> to the network via a normal link.
>>>> 
>>>> Do you still object to the draft?
>>>> 
>>>> Thanks,
>>>> 
>>>> ŠGeorge
>>> 
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