From: "Eric Voit (evoit)" <evoit@cisco.com>
To: Martin Bjorklund <mbj@tail-f.com>, "zhoutianran@huawei.com"
 <zhoutianran@huawei.com>
CC: "alexander.clemm@huawei.com" <alexander.clemm@huawei.com>,
 "netconf@ietf.org" <netconf@ietf.org>, "zhengguangying@huawei.com"
 <zhengguangying@huawei.com>
Thread-Topic: a joint discussion on dynamic subscription
Thread-Index: AdQCx01ede4gaRHPTgG2WyMdkd0r2gARka+AADD1vgAABGEosA==
Date: Thu, 14 Jun 2018 14:19:33 +0000
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 <b256b91c7cbc4b3093c858e55c912f88@XCH-RTP-013.cisco.com>
 <20180614.091828.21142123428745204.mbj@tail-f.com>
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Subject: Re: [Netconf] a joint discussion on dynamic subscription
Precedence: list

> From: Martin Bjorklund, June 14, 2018 3:18 AM
>
> Hi,
>=20
> "Eric Voit (evoit)" <evoit@cisco.com> 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.
>=20
> Cool!  I think that this should be explcitly described in the subscribed-
> notifications document.

Right now it is explicitly described in the RESTCONF-notif draft.  But I se=
e your point on adding it as guidance for future transports like Tianran's.=
  So I added the following to the "Transport Requirements" (section 5.3):

A specific transport specification built upon this document may or may not =
choose to require the use of the same logical channel for the RPCs and the =
event records.  However the event records and the subscription state notifi=
cations MUST be sent on the same transport session to ensure the properly o=
rdered delivery.

=20
> In the case of RESTCONF, decision to use a separate channel for the notif=
s is
> implicit in the transport of the request to establish-subscription.
>=20
> In the case of UDP, I think the idea is that the establish-subscription i=
s sent
> over any protocol that can do RPCs (NETCONF, RESTCONF, ...), but then som=
e
> specific input parameter informs the server that the notifs are supposed =
to be
> sent over some other transport.
>=20
> While reading the text about sessions, I found this:
>=20
> In 2.4.3:
>=20
>    The "modify-subscription" operation permits changing the terms of an
>    existing dynamic subscription established on that transport session
>    via "establish-subscription".
>=20
> Which session does "that transport session" mean?  Perhaps simply:
>=20
> NEW:
>=20
>    The "modify-subscription" operation permits changing the terms of an
>    existing dynamic subscription.

Change made. =20

As this change does impact NETCONF-notif, I placed the following requiremen=
t in that document's "Dynamic Subscription" section.

For a dynamic subscription a "modify-subscription", "delete-subscription", =
or "resynch-subscription" RPC MUST be sent using same the NETCONF session u=
pon which the referenced subscription was established.".

Eric

> > > 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.
>=20
> But this is an implementation detail.  However, it is true that the speci=
fication
> 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.
>=20
>=20
> /martin
>=20
>=20
>=20
> > 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
> >