Re: [Netconf] Issue SN #4: Can Transport vary across different receivers of a single configured subscription?

In the meeting room discussion during the NETCONF WG, sentiment was to use a common Transport across all receivers of a single configured subscription.   This was proposal (2) below.

I would like to see if there is any objection to this.   If not, we can close this issue in a few weeks.

Eric

> -----Original Message-----
> From: Netconf [mailto:netconf-bounces@ietf.org] On Behalf Of Eric Voit
> (evoit)
> Sent: Thursday, November 16, 2017 3:30 AM
> To: Martin Bjorklund <mbj@tail-f.com>; Einar Nilsen-Nygaard (einarnn)
> <einarnn@cisco.com>
> Cc: netconf@ietf.org
> Subject: Re: [Netconf] Issue SN #4: Can Transport vary across different
> receivers of a single configured subscription?
> 
> Hi Martin,
> 
> Yes, I originally had both your options in the WG slides.    I removed (A)
> after discussion with Mahesh for the WG session slides to simplify the in-
> room discussions, as well as consideration of the points Einar makes below.
> We can of course have more and deeper resolution discussions here.
> 
> Thanks,
> Eric
> 
> > -----Original Message-----
> > From: Martin Bjorklund [mailto:mbj@tail-f.com]
> > Sent: Thursday, November 16, 2017 2:54 AM
> > To: Einar Nilsen-Nygaard (einarnn) <einarnn@cisco.com>
> > Cc: Eric Voit (evoit) <evoit@cisco.com>; netconf@ietf.org
> > Subject: Re: [Netconf] Issue SN #4: Can Transport vary across
> > different receivers of a single configured subscription?
> >
> > Hi,
> >
> > Note that the issue is that the current model has:
> >
> >       +--rw subscription* [identifier]
> >          ...
> >          +--rw encoding
> >          ...
> >          +--rw receivers
> >             +--rw receiver* [address port]
> >                ...
> >                +--rw protocol
> >
> > My proposal is have encoding and protocol together:
> >
> > (A)
> >       +--rw subscription* [identifier]
> >          ...
> >          ...
> >          +--rw receivers
> >             +--rw receiver* [address port]
> >                ...
> >                +--rw protocol
> >                +--rw encoding
> >
> > or:
> >
> > (B)
> >       +--rw subscription* [identifier]
> >          ...
> >          +--rw encoding
> >          +--rw protocol
> >          ...
> >          +--rw receivers
> >             +--rw receiver* [address port]
> >                ...
> >
> > I think that this is *less* complex and probably more optimal than the
> > current solution.
> >
> > "Einar Nilsen-Nygaard (einarnn)" <einarnn@cisco.com> wrote:
> > > Martin,
> > >
> > > As yet, we have no practical use cases where we would have a single
> > > configured subscription with multiple receivers who wish to receive
> > > the data in different formats. Thus supporting this seems like an
> > > unnecessary complexity for platforms, and one which potentially
> > > impacts optimisations that we already use in some platform
> > > implementations (e.g. sending the same encoded PDU to multiple
> > > receivers, relieving the platform of encoding the same data multiple
> > > ways).
> >
> > But this optimization doesn't really work, as you note below (*).
> >
> > > Of course, if a client really wants to have the same data sent to
> > > multiple receivers but in different formats, they can do this — just
> > > provision separate subscriptions with the same filter.
> >
> > Exactly; this is more complex and less optimal since the same filter
> > might be evaluated twice, unless you add code to optimize for that
> > (which probably falls in your category of "unnecessary complexity").
> >
> > (*) So if the operator requires this setup, he will have to configure
> > two different subscriptions today.  Thus, the platform will encode the
> > data twice, and your optimization above won't help.
> >
> > > All-in-all, I don’t see any benefit in making the base model support
> > > this, only downsides, so do you have any specific use cases in mind
> > > where this would be a benefit? So far in the use cases we have
> > > looked at in SP, DC, enterprise and IoT we have not seen any
> > > requirement to support this, but we have seen the need for multiple
> receivers (e.g.
> > > to support HA/redundancy approaches).
> >
> > The current model supports different *protocols* for the different
> > receivers.  Do you have a use case supporting that, or would (B) above
> > fulfil your requirements.
> >
> >
> > /martin
> >
> >
> >
> > > As such, I would be
> > > reluctant to add this to the draft at this stage when the
> > > functionality can be achieved already if absolutely necessary.
> > >
> > > Cheers,
> > >
> > > Einar
> > >
> > >
> > > > On 15 Nov 2017, at 21:53, Eric Voit (evoit) <evoit@cisco.com> wrote:
> > > >
> > > > Adding Einar as he had some strong opinions on this a few years
> > > > ago when we were setting the model...
> > > >
> > > >
> > > >> From: Martin Bjorklund, November 15, 2017 10:43 AM
> > > >>
> > > >> "Eric Voit (evoit)" <evoit@cisco.com> wrote:
> > > >>> Hi Martin,
> > > >>>
> > > >>>> From: Martin Bjorklund [mailto:mbj@tail-f.com]
> > > >>>>
> > > >>>> "Eric Voit (evoit)" <evoit@cisco.com> wrote:
> > > >>>>> In the WG session tomorrow, I am hoping to get "hum feedback"
> > on:
> > > >>>>>
> > > >>>>>
> > > >>>>>
> > > >>>>> draft-ietf-netconf-subscribed-notifications
> > > >>>>>
> > > >>>>> https://github.com/netconf-wg/rfc5277bis/issues/4
> > > >>>>>
> > > >>>>>
> > > >>>>>
> > > >>>>> The two choices and their issues exposed during the two week
> > > >>>>> review on
> > > >>>> "Can Transport vary across different receivers of a single
> > > >>>> configured subscription?" are:
> > > >>>>>
> > > >>>>>
> > > >>>>>
> > > >>>>> (1) Yes, Transport can vary by receiver
> > > >>>>>
> > > >>>>> *        Fewer subscriptions (scale benefit)
> > > >>>>>
> > > >>>>> *        Can convert transport without requiring an application to
> > learn
> > > >> a
> > > >>>> multiple subscription ids
> > > >>>>>
> > > >>>>> *        No duplication of content during transport conversion.
> > > >>>>>
> > > >>>>> *        (Potential confusion in allowing transport to vary, but
> > > >>>>> *        encoding
> > > >> not
> > > >>>> to vary?)
> > > >>>>>
> > > >>>>>
> > > >>>>>
> > > >>>>> (2) No, only one Transport across all subscriptions
> > > >>>>>
> > > >>>>> *        Simpler model
> > > >>>>>
> > > >>>>> *        But applications may need to create and track multiple
> > > >>>> subscription-ids for the same content.
> > > >>>>>
> > > >>>>> *        Temporary duplication of content streams during transport
> > > >> change.
> > > >>>>>
> > > >>>>>
> > > >>>>>
> > > >>>>> The current draft does (1).
> > > >>>>
> > > >>>> Actually, the github issue lists 3 options, but here you just list 2.
> > > >>>
> > > >>> In reviewing tomorrow's slides with Mahesh, he preferred 2
> options.
> > > >>> And as varying the encoding by receiver seems unlikely in
> > > >>> implementation
> > > >>
> > > >> Why is this unlikely?  Suppose I have two receivers for the same
> > > >> subscription, one wants NETCONF/XML and the other
> > RESTCONF/JSON.
> > > >> Is that unlikely?
> > > >
> > > > Einar's belief was that a publisher implementation would be
> > > > unlikely to service a single subscription into multiple encodings.
> > > > If such a condition existed, it would be far easier to create two
> subscriptions.
> > > > This also would have fewer error conditions.
> > > >
> > > >>> , there is little reason to socialize this unlikely variant before
> > > >>> the whole WG.   Since as your opinion was either both encoding
> and
> > > >>> transport or neither encoding and transport vary by receiver,
> > > >>> the more likely of your primary ask is supported.
> > > >>>
> > > >>>
> > > >>>> I think the point is that in the term "Transport", we need to
> > > >>>> include both protocol and encoding (in the case the protocol
> > > >>>> supports multiple encodings).
> > > >>>
> > > >>> While most likely the case for NETCONF and RESTCONF, Tianran's
> > > >>> draft-ietf-netconf-udp-pub-channel shows that there can be
> encoding
> > > >>> variation by transports .   It Therefore it seems better to let them
> > > >>> both vary independently.
> > > >>
> > > >> Not sure I understand what you mean.  To be clear, do you think
> > > >> the "encoding" leaf should stay where it is, or be moved down to
> > > >> the receiver, as a sibling to "protocol"?
> > > >
> > > > Encoding leaf should stay where it is.  Your previous ask was to
> > > > put encoding and transport and the same level. There is an option
> > > > proposed in the slides which does that.
> > > >
> > > > Eric
> > > >
> > > >> /martin
> > > >
> > >
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