Re: [Ibnemo] [Sdn] Defining a Common Model for intent

["Susan Hares" <[e-mail]>]

Dave:  

 

Thanks for the critique - I really appreciate you refining my concepts.   My
ideas arose out of an informal discussion with Kareeti Kompella at IPOP 2015
on Nemo Intent vs. Juniper's Declarative policy.  However, let me sharpen my
pencil and go back to the Stanford formal papers and other to work the proof
forward.   

 

Sue 

 

From: Ibnemo [mailto:[e-mail]] On Behalf Of Dave Hood
Sent: Tuesday, June 02, 2015 7:48 PM
To: Susan Hares; 'Lifengkai (Fengkai)'; [e-mail]
Cc: [e-mail]
Subject: Re: [Ibnemo] [Sdn] Defining a Common Model for intent

 

Sorry, Sue, but IMO this just introduces new undefined terms: 

 

Declarative - your example looks like an imperative to me. How do I know
what is *not* a declarative? X = y + z? Declarative or imperative? I'm not
playing games here, I really don't understand how we would distinguish. 

 

Policy - In the SDN architecture, we define pretty clearly what we mean by
policy. It is a constraint imposed by a manager that governs the behaviour
of a tenant/client/app. But it's not clear what the meaning would be in the
present context.

 

I wonder whether the context you mention (of which I have also not seen a
clear definition) is subsumed in the API offered to the tenant/client/app.
If I expose a catalog of services at an interface, each service possibly
with some options, then have I defined a context for the user of that API?
That seems to me to make sense, but is again subject to the observation that
any and all APIs expose some subset of the universe, so it isn't apparent
what is *not* a context.

 

Good conversation, please continue. I hope we will all learn something by
pushing on these ideas.

 

Dave

 

From: Susan Hares [mailto:[e-mail]] 
Sent: Tuesday, June 02, 2015 4:23 PM
To: Dave Hood; 'Lifengkai (Fengkai)'; [e-mail]
Cc: 'Zhoutianran'; 'Xiayinben'; [e-mail]
Subject: RE: [Sdn] Defining a Common Model for intent

 

Dave:

 

Thank you for restating your excellent question.  "How do we know
[something] is not intent?"  

 

Let me start an assertion that Intent is declarative policy applied to a
context.  If you accept this assertion, 

Then:

1)      You can tell if the policy is prescriptive rather than
declarative/intent, 

2)      You can tell whether a declarative policy is presented with a
context. 

 

An example of declarative policy is, connect London and New York with 1 Gbps
data flow between.  How, when, where and why with what - is left up to the
fulfillment of the intent.  The context is networking and business offices.


 

Do you think I'm on the right track? 

 

Sue 

From: Dave Hood [mailto:[e-mail]] 
Sent: Tuesday, June 02, 2015 9:26 AM
To: Lifengkai (Fengkai); Susan Hares; [e-mail]
Cc: Zhoutianran; Xiayinben; [e-mail]
Subject: RE: [Sdn] Defining a Common Model for intent

 

I agree that the context matters, Fengkai (and Susan in earlier response).
What the I-D appears to be saying is that any interaction across an NBI is
intent: otherwise the app/tenant/customer wouldn't do it. That's the root of
my question from the beginning: how would we know what is *not* intent?

 

If I ask for some particular microscopically detailed configuration (a
"how"), it's because I care, for some reason, about that level of detail. It
is in fact part of my intent. 

 

In my IT example, I argue that intent need not be independent of protocols
and ports, and that it need not be portable. Your response about context
appears to agree.

 

So as best I can tell, we can say precisely what an intent is, and we can't
say what an intent is not. If intent is just the latest buzzword, which it
certainly appears to be, can we just say so and leave it to the marketing
people?

 

Dave

 

From: Lifengkai (Fengkai) [mailto:[e-mail]] 
Sent: Tuesday, June 02, 2015 12:47 AM
To: Dave Hood; Susan Hares; [e-mail]
Cc: Zhoutianran; Xiayinben; [e-mail]
Subject: RE: [Sdn] Defining a Common Model for intent

 

Hi Dave and all,

 

Thanks for proposing the two valuable intent use cases.

 

For the use case 2, I agree that the IT employee needs to include the
details of ports/protocols into his/her intent descriptions, but those may
not be in the intent context scope of a non-IT employee. Have a further
consideration with this, different users of the network have their own
intent in a specific domain. Then the roles/actors of network users, such as
end users, application developers, tenant IT/network administrators,
operator network administrators, are valuable to be identified and
distinguished, thus fitting the intent requirements of the network users
with different roles.

 

Any thoughts about this consideration?

 

 

Best Regards,

Fengkai

 

From: sdn [mailto:[e-mail]] On Behalf Of Dave Hood
Sent: Tuesday, June 02, 2015 1:38 AM
To: Susan Hares; [e-mail]
Cc: Zhoutianran; Xiayinben; [e-mail]
Subject: Re: [Sdn] Defining a Common Model for intent

 

An excerpt from an email I sent on the ONF NBI list, which may contain some
useful thoughts:

 

I have always had trouble understanding what an intent really is, so I am
looking forward to making the concept more precise.

 

When I click a link on a web page, I express an intent to invoke whatever
that link offers. Completely below the surface is a layer stack, on-demand
session establishment, DNS look-ups, server load balancers, and any number
of other technological features that are of no interest to me. Why not use
that as an example of intent?

 

Better yet, we talk about negotiation and selection. Suppose I want to buy a
widget. I probably already have some idea whether I want to go to Amazon or
EBay or somewhere else. Suppose it's Amazon. I search Amazon's catalog and
receive an offer of several widgets, some new, some used, some with a choice
of colour or other pertinent features. If I see nothing I like, I may open a
new browser window and check out Best Buy or EBay (lots more hidden
technology to make that happen!). Maybe I come back to the Amazon page,
having found nothing I liked better somewhere else. Now I accept one of the
offered widgets and go through the checkout process. 

 

Do we agree that this is a fairly pure expression of intent as
conceptualized in the paper? (If not, let's talk about making a Skype call.)

 

Ok, that's my intent as an internet user. Let's assume the network is all
SDN of one kind or another. I invoke my intent through a GUI onto software
local to my PC, but I don't think we can call the PC an SDN controller. It's
more an active mediator, a client to an SDN. As far as the network is
concerned, the client makes DNS queries and swaps opaque TCP packets over a
forwarding path that may already exist, or may need to be learned and set up
on demand. This is about right, because the session content may well be
encrypted end to end, and rightly.

 

To the SDN controller, my intent is satisfied by directing DNS queries to a
known DNS server somewhere, and ensuring IP connectivity for the subsequent
session. Hmmm. what happened to our intent-based NBI? The SDN offered my PC
a packet interface with the properties of knowing how to recognize and route
DNS queries specially, and general IP connectivity. My PC accepted the
service offer implicitly by offering traffic to the data-plane interface.
The network could be performing associated auxiliary services such as
usage-based billing (think wireless roaming), so it's more than just a dumb
pipe.

 

If this is not a legitimate example of intent, it would be good to write the
white paper in such a way that clearly excludes such cases.

 

Use case 2: suppose I am a corporate IT employee, and suppose that my intent
is to have an E-Line between two of my campi. I necessarily care about ports
and protocols; talk about intent being portable and protocol independent
continues to confuse me completely. How can I order an E-line without caring
about such details? [Nor is this intent portable.]

 

Obviously, an SDN controller is going to expose whatever actions and
elements of information are germane to the service it offers, and if ports
and protocols are germane to the service, so be it.

 

The SDN architecture, being recursive, models the north side of any
controller as exposing an instance of an information model, customized for
the intended client/customer/app/user. That being the case, how do we
distinguish an NBI API that conveys intent (service: same thing?) from one
that does not?

 

I have recently come to the view that granularity is the criterion by which
an intent or service invocation is distinguished. Colloquially speaking, a
service invocation is a single invocation across the API: give me E-Line.
Now of course this turns into constraint negotiation, offer and acceptance,
but what happens across the API is effectively one transaction. In contrast,
what we might agree is *not* an intent or a service is the manipulation of a
granular information model, the explicit visibility of multiple objects, how
they are interrelated, their attributes, and the like.

 

.         Network as a single lump vs some non-trivial topology.

 

.         Chauffeur vs driving a car. Legitimate reasons to choose one
option or the other, but the level of granularity is quite different. Shall
we agree that driving is too granular to be considered intent?

 

This idea of granularity and detailed operations on the components (which of
course may be complex entities themselves, virtualized into simple-appearing
lumps) seems to me to capture the essence of what people are talking about
when they say intent or service. I am not comfortable with the way I am
expressing it, so if this is a step in a productive direction, or even if
it's not, I welcome suggestions to clarify the concept.

 

Dave

 

From: sdn [mailto:[e-mail]] On Behalf Of Susan Hares
Sent: Saturday, May 30, 2015 1:02 PM
To: [e-mail]
Cc: 'Zhoutianran'; 'Xiayinben'; [e-mail]
Subject: [Sdn] Defining a Common Model for intent

 

On this mail list, there has been a discussion of two types of information
for Intent and Nemo:
(http://www.ietf.org/mail-archive/web/sdn/current/msg00646.html) :

 

1)      What information is needed to represent a service request, 

2)      How to represent and transport the information for a request.

 

In order to define what information is needed to represent a 1) service
request that signals Intent from an application to a controller, it is
important to define Intent, and provide a clear model of Intent.  Also, in
describing real use-cases it is important that one uses the same definition
and model for Intent in each use case.   

 

In the current forums examining Intent (ODL NIC, ODL Nemo, OF NBI and
Keystone, OPNFV Movie, OpenStack) there is a realization that Intent occurs
at multiple layers.  The authors of draft-xia-ibnemo-icim have created a
definition for intent and a unified model for defining intent which can
handle 1 or multiple layers. The model suggest that:

1)      A user has a intent that is expressed in a context.

2)      Intent (usually) involves an object with a result, and optionally
includes operations toward that result. 

3)      Operations conditions perform actions within/modified by
constraints. 

 

We believe this defines clearly what others are calling "pure intent"
(objects + results) versus "constrained intent" (objects + operations +
constraints).   The draft can be found at:
https://datatracker.ietf.org/doc/draft-xia-ibnemo-icim/ .   The authors are
looking for feedback on the concepts in the draft.   

 

Sue Hares