Re: [Netconf] a joint discussion on dynamic subscription

["Eric Voit (evoit)" <[e-mail]>]

> From: Tianran Zhou, June 14, 2018 8:38 AM
> 
> Hi,
> 
> > -----Original Message-----
> > From: Martin Bjorklund [mailto:[e-mail]]
> > Sent: Thursday, June 14, 2018 3:18 PM
> > To: [e-mail]
> > Cc: Tianran Zhou <[e-mail]>; Alexander Clemm
> > <[e-mail]>; Zhengguangying (Walker)
> > <[e-mail]>; [e-mail]
> > Subject: Re: a joint discussion on dynamic subscription
> >
> > Hi,
> >
> > "Eric Voit (evoit)" <[e-mail]> wrote:
> > > Hi Tianran,
> > >
> > > > From: Tianran Zhou, June 12, 2018 11:47 PM
> > > >
> > > > Hi Eric,
> > > >
> > > > When we are discussing the draft-ietf-netconf-udp-pub-channel, we
> > > > find a conflict with current dynamic subscription design.
> > > > 1. The dynamic subscription requires notification to use the same
> > > > channel as the subscription.
> > >
> > > This is true when you look at the NETCONF transport draft.  However
> > > this is *not* required by the base subscribed-notification draft.
> > > And in fact, the HTTP transport draft might not use the same logical
> > > channel.  E.g., see how the URI is returned within:
> > > https://github.com/netconf-wg/notif-restconf/blob/master/draft-ietf-
> > > ne
> > > tconf-restconf-notif-05.txt
> > >
> > > So if you wanted to define some transport session independence for a
> > > UDP transport, subscribed-notifications should permit that.  And if
> > > you believe there is something in the text which prohibits this, let
> > > me know.
> >
> > Cool!  I think that this should be explcitly described in the
> > subscribed-notifications document.
> >
> > In the case of RESTCONF, decision to use a separate channel for the
> > notifs is implicit in the transport of the request to establish-subscription.
> >
> > In the case of UDP, I think the idea is that the
> > establish-subscription is sent over any protocol that can do RPCs
> > (NETCONF, RESTCONF, ...), but then some specific input parameter
> > informs the server that the notifs are supposed to be sent over some other
> transport.
> 
> Yes. I did not see this is the current RPC. Maybe similar the configured
> subscription, to describe transport of the receiver.

draft-ietf-netconf-restconf-notif contains a YANG model and examples showing how transport specific parameters can be augmented to the "establish-subscription RPC".  Search the document for "URI".

On other addition...  Several months ago we chatted that the multi-channel line-card separation and the UDP transport might be supported by different YANG models.  This should allow any parameters needed for multi-line card to be supportable without also requiring the corresponding implementation to also support UDP transport.

Eric

> > While reading the text about sessions, I found this:
> >
> > In 2.4.3:
> >
> >    The "modify-subscription" operation permits changing the terms of an
> >    existing dynamic subscription established on that transport session
> >    via "establish-subscription".
> >
> > Which session does "that transport session" mean?  Perhaps simply:
> >
> > NEW:
> >
> >    The "modify-subscription" operation permits changing the terms of an
> >    existing dynamic subscription.
> >
> >
> > > > 2. The RPC does not have the input information about the receiver
> > > > because the above assumption.
> > > >
> > > > However, when we talk about the distributed data collection (multi
> > > > data originators), the publication channel is always different
> > > > from the subscription channel.
> > >
> > > While it likely isn't what you want, even with NETCONF, the single
> > > NETCONF session doesn't means that distributed line card generation
> > > of the notification messages is impossible.  For example, the
> > > inclusion of the header object message-generator-id (as defined
> > > within
> > > draft-ietf-netconf-notification-messages) allows the notification
> > > message generation to be distributed onto linecards even if the
> > > messages themselves are still driven back to a central transport
> > > session.  Note that I am not recommending this, but the
> > > specifications would support this.
> > >
> > > > So either the distributed data collection does not support dynamic
> > > > subscription, or current dynamic subscription definition may need
> > > > modification.
> > >
> > > I think for UDP, you will want to define a way to bind the lifecycle
> > > of the dynamic subscription's channels across multiple line cards.
> > > This will require some thinking as well as coordination within the
> > > publisher.
> >
> > But this is an implementation detail.  However, it is true that the
> > specification must work out the fate-sharing details between the
> > session that sent the establish-subscription and the notif channel.
> > Just as in the "restconf" draft.
> 
> We can just describe this fate-sharing requirement explicitly in the document.
> On implementation, I do not think it's hard to bind the lifecycle of the
> subscription channel and the publication channel.
> 
> > /martin
> >
> >
> >
> > > Perhaps returning multiple URIs (one for each linecard) might be
> > > something which could make this easier.  If you go down this path,
> > > you still will need to fate-share the lifecycle of the subscription
> > > across all of those line cards.
> > >
> > > Eric
> > >
> > > > What's your thoughts?
> > > >
> > > > Regards,
> > > > Tianran
> > >