Re: [CCAMP] Objective function draft

Dieter Beller <> Thu, 20 September 2012 00:18 UTC

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Hi all,

the terms UNI and E-NNI are defining reference points or boundaries if you will between
a user (device) and a network (device) and between network domains, respectively
(see RFC4208 or ITU-T G.8080). These reference points are located on data plane links
between two network devices. Hence, the information that is exchanged across these
reference points, ie.e, the infomation on either end of the link is exactly the same, which
means that no network layer is crossed at these reference points! Therefore, these
reference points are associated with a horizontal interface between the devices (same
network layer).

Now, orthogonal to that, we have layer transitions in the date plane if we are in a multi-layer
environment which means that a client signal is encapsulated into a server layer signal and
then carried transparently across the server layer network.
This is a data plane client/server relationship and we better talk about data plane layer
transitions and do not link these vertical inter-layer relationships to the terms UNI or E-NNI
because they have a different meaning as described above. If we are sloppy regarding
terminology we may end up creating a lot of confusion.

I am in agreement with those who have posted similar messages.


On 19.09.2012 20:22, Lou Berger wrote:
        I sympathize with Julien's comments.  It seems to me that the draft
intermingles the concepts of multi-domain (which includes UNI/ENNI) and
multi-layer (which includes, for example MPLS over optical).  While
there certainly is much commonality in mechanisms, I think the draft
could be clearer on the conceptual definitions and discussions...


On 9/19/2012 1:00 PM, Gert Grammel wrote:
Lets try to be more precise and write instead:

- "this document uses the term 'External Network Interface (E-NNI)' to describe this interface between two network domains. Both domains may switch on different layers and form a client/server relationship.

Although I agree with better readability of the BCP, we have to address the concern of the WG and be precise. So let's try perfecting our language ...


From: on behalf of Igor Bryskin
Sent: Wednesday, September 19, 2012 12:25:58 PM
To: Julien Meuric; John E Drake
Subject: Re: [CCAMP] Objective function draft

Hi Julien,

This should say:
- "this document uses the term 'External Network Network Interface (E-NNI)' to describe this interface between a client and server network domains".

The important thing is that there is a TE domain demarcation between network and its client. The similar demarcation exists between adjacent network domains in a multi-domain environment. In either case the domains are inter-connected via access/inter-domain links in the data plane and GMPLS-ENNI in the control plane.

Hope this helps.

-----Original Message-----
From: [] On Behalf Of Julien Meuric
Sent: Wednesday, September 19, 2012 11:59 AM
To: John E Drake
Subject: Re: [CCAMP] Objective function draft

Hi John.

Let me quote the introduction of draft-beeram-ccamp-gmpls-enni:
- "this memo describes how introducing a representation of server layer network resources into a client layer network topology enhances client layer networking in the overlay model";
- "this document uses the term 'External Network Network Interface (E-NNI)' to describe this interface between a client and server network".

E-NNI for client-server (and overlay): this is exactly where I start to get confused... (draft-beeram-ccamp-gmpls-uni-bcp used to be easier to follow on this.)


On 09/19/2012 16:03, John E Drake wrote:

This is the terminology we have been using in draft-beeram.

Yours irrespectively,


-----Original Message-----
From: [] On
Behalf Of Julien Meuric

Lou, Gert,

You are right: my previous 1st sentence was too specific,
"inter-layer signaling" should be replaced by "client-server
signaling". We agree on that, it was not my intention to question that part.



Le 19/09/2012 13:46, Lou Berger a écrit :
    Just to add to Gert's point about UNI/ENNI not being related to
layers; you can find the same terminology in the context of MPLS-TP,
see RFCs
6215 and 5921.  We already have RFC4208 which provides the
foundation of a GMPLS UNI, and the related RFC5787(bis) work.

I personally see this as the foundation and context for this (and
beeram) discussion.


On 9/19/2012 3:14 AM, Gert Grammel wrote:
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
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
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
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.

-----Original Message-----
From: JP Vasseur (jvasseur) []

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"
<> 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
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.


Le 17/09/2012 23:22, Gert Grammel a écrit :
Hi George,

The objective function is in the end a routing information.
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,
is the wrong choice. ENNI should be considered instead and Draft-
beeram-ccamp-gmpls-enni would be a good starting point.

From: on behalf of George Swallow

Hi Julien -

On 9/17/12 9:37 AM, "Julien Meuric" <>
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
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
(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
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
doing the layer dimensioning). Thus, I feel this trade-off in
selection tuning is rather unlikely to happen and I fear we may
talking about RSVP-TE over-engineering here.
The idea is simply to allow the client to express its
The UNI-N remains in control.  By policy it can use the objective
function or not.  Further if it does use the objective function
fails to find a path it can either say that there was no path or
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.




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
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?


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