Re: [netmod] questions about draft-rtgyangdt-rtgwg-device-model-00

Martin Bjorklund <mbj@tail-f.com> Wed, 26 August 2015 10:41 UTC

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Date: Wed, 26 Aug 2015 12:41:29 +0200 (CEST)
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To: lberger@labn.net
Subject: Re: [netmod] questions about draft-rtgyangdt-rtgwg-device-model-00
From: Martin Bjorklund <mbj@tail-f.com>
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Lou Berger <lberger@labn.net>; wrote:
> Martin,
> 	Sorry for the delayed response, was away for a bit.  Not sure if any of
> this is OBE as just starting to catch up on mail.
> 
> On 08/20/2015 03:58 AM, Martin Bjorklund wrote:
> > Lou Berger <lberger@labn.net>; wrote:
> >> Martin,
> >>
> >> See below.
> >> On 08/19/2015 05:27 AM, Martin Bjorklund wrote:
> >>> Hi,
> >>>
> >>> Lou Berger <lberger@labn.net>; wrote:

[...]

> >> Deeper in the hierarchy the path becomes more significant, but you
> >> weren't really questioning this.
> > 
> > I am all for significant nodes in the path!  
> 
> This is really good/useful to hear.  If disagreement is limited to the
> top level node, it's much easier (but not easy ;-) problem to solve.
> 
> > My point is that /device
> > is insignificant.
> 
> I think the fundamental discussion here, is who get's to say what's
> significant and we have (at least) two opposing views on this point.
> 
> From my standpoint it comes down to how you view full set of models that
> may be seen.  From the device view, you might only (or, more likely,
> mostly) see models under /device -- so device doesn't add much value.
> BUT from the controller/NMS/EMS (or whatever you want to call it) view,
> you're likely to see all the models

Agreed, but see below.

> so /device plays a much more
> significant role in identifying logical model
> organization/understanding.  -- That said, I'm much more of a device
> person than an NMS builder, so I'm also willing to trust the opinion of
> folks who are clearly doing significant work on the controller/NMS
> side.

[This was briefly discussed in another mail thread, and I'll repeat it
here.]

On the controller, you probably have a list of devices you control
(this is how our NCS works, and how ODL works (I have been told)):

  container devices {
    list device {
      key name;
      // meta-info about the device goes here, things like
      // ip-address, port, auth info...
      container data {
        // all models supported by the devices are "mounted" here
      }
    }
  }

So on the controller, the path to interface "eth0" on device "foo"
would be:

  /devices/device[name='foo']/data/interfaces/interface[name='eth0']

if we also have a top-level "/device" container we'd have:

  /devices/device[name='foo']/data/device/interfaces/interface[name='eth0']


(here you again can see that the "device" node in the device model
doesn't make much sense)


The path is scoped in the system you work with; in the controller it
might be as I illustrated above, in the device it starts with
/interfaces.  But then you might also have a
controller-of-controllers. where the path might be:

  /domains/domain[name='bar']/devices/device[name='foo']/data
    /interfaces/interface[name='eth0']

Pushing all these concepts down into the device model clearly doesn't
help...


/martin