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

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

Stuart: 

In some ways, the policy continuum (Davy, Jenning, Strassner) suggest the
layer of models (as ISO did) of business, system, administrator,  device,
and instance. 

I agree with you theoretically that "data model for intent might/should be
different at each level".  There is code-evidence that backs up your point.
The flexibility the Nemo early proof-of-concept demo is enhanced by the
ability to allow a data model to be pass to the controller.  The user really
just needs to signal "intent" and the model passes the context.   Nemo uses
a simple combination of entities, endpoints and connections. 

If we expanded this from the top-down, then the data model would have the
simple context of the user.  As it goes down, the model would get augment
with the context of each layer.  Much like the tree with roots at the top.  

This is a fascinating part of the discussion - can you add more details to
your comments? 

Sue 
-----Original Message-----
From: sdn [mailto:[e-mail]] On Behalf Of STUART VENTERS
Sent: Tuesday, June 02, 2015 12:06 PM
To: [e-mail]
Cc: 'Dave Hood'; [e-mail]; Lifengkai (Fengkai); Zhoutianran;
Xiayinben; Susan Hares
Subject: Re: [Sdn] Defining a Common Model for intent



I have 2 cents to contribute for this fuzzy intent word and resulting data
model.
Perhaps 'intent'  is just a relatively high level service request.
The problem with this definition is what is that 'relatively high level'
appears to depend on your point of view.

To help think about it, here's a long chain of command for the same action.
It is long for fun and so that anybody can find part of it that they
recognize.


Chain of command:

Investor says: make money
CEO says: make the network work
CIO says: give me bandwidths between sites A, B, and C Net engineer says: I
need these evc's to these endpoints Purchasing agent: Says use this product
from this vendor Sales Person says: Here is the price and priority
Partitioner: divides the end to end circuit among administrative domains
Planner: picks the necessary resources to use, makes the truck rolls happen
Allocator: allocates the necessary bandwidth
Provisioner: decides what provisioning is necessary in each part of the path
Adaptor: tailors the provisioning to a specific box
Driver: pushes the provisioning into the forwarding tables Forwarding
engine: forwards according to the tables

The Investor's statement at the top is clearly what and not how.
The forwarding engine's operations have a lot of how, but maybe little
global view of what we are doing overall.

If we say that the top is intent and the bottom is a is service request,
  who's to say where intent stops and service requests start?

Perhaps  'intent' means a service request coming from a higher layer for
refinement.

That said, the data model for intent might/should be different at each
level.
Since each level is processing the same request at different levels of
detail, it might be similar at each level.
Perhaps the data model starts simple on top and gathers more and more detail
as it gets lower ?
Maybe like a tree with the root at the top and leaves at the forwarding
engines, except distributed.

Perhaps a simple starting point near the top is a combination of entities,
endpoints, and connections.


Regards,

Stuart Venters







From: sdn [mailto:[e-mail]] On Behalf Of Dave Hood
Sent: Tuesday, June 02, 2015 8:26 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 

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