Re: [Netconf] a joint discussion on dynamic subscription

[Tianran Zhou <[e-mail]>]

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.

> 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
> >