[Standards] Rayo feedback.

Ben Langfeld ben at langfeld.me
Thu Sep 3 19:15:52 UTC 2015


On 2 September 2015 at 12:55, Dave Cridland <dave at cridland.net> wrote:

> (Matthew Miller prodded me that I hadn't replied to this).
>
> On 18 August 2015 at 12:39, Ben Langfeld <ben at langfeld.me> wrote:
>
>> On 18 August 2015 at 08:13, Dave Cridland <dave at cridland.net> wrote:
>>
>>>
>>>
>>> On 17 August 2015 at 20:15, Ben Langfeld <ben at langfeld.me> wrote:
>>>
>>>>
>>>>
>>>> On 17 August 2015 at 13:44, Kevin Smith <kevin.smith at isode.com> wrote:
>>>>
>>>>> On 14 Aug 2015, at 20:11, Ben Langfeld <ben at langfeld.me> wrote:
>>>>> > > 2) 5.1 (Actors) places requirements that these JIDs for
>>>>> components/mixers can only be only be under subdomains - why is this?
>>>>> AFAIK, this is the only part of XMPP that implies any relationship between
>>>>> a domain and a subdomain, and it doesn’t immediately seem like a useful
>>>>> restriction.
>>>>> > >
>>>>> > > Not true. The word I used was "perhaps". This is simply to point
>>>>> out that full JIDs must be used to address these entities and no
>>>>> relationship between domains may be assumed.
>>>>> >
>>>>> > I think that at least the table in 5.2 is quite explicit in
>>>>> requiring things to be a subdomain - I take it this wasn’t intended.
>>>>> >
>>>>> > Actually quite the opposite:
>>>>> >
>>>>> > > where elements in square brackets are optional
>>>>> >
>>>>> > <call ID>@[<call sub-domain>.]<service domain>/<component ID>
>>>>> >
>>>>> > Quite explicitly optional, I'd say.
>>>>>
>>>>> Sorry, badly expressed. It is optional that it’s a *sub*domain, yes.
>>>>> But if it’s not the service domain, you’re requiring it to be a subdomain
>>>>> of the service domain. This is what I was calling out - this is a unique
>>>>> requirement in XMPP; there’s usually no formal relationship between
>>>>> different domains like this, and it’s not clear to me that one is needed
>>>>> here.
>>>>>
>>>>>
>>> I'd like to see the answer to this one. Given a server of
>>> shakespeare.lit, do I understand that a call must be within either that
>>> domain or a subdomain of it?
>>>
>>
>> I guess that's what this implies. I have yet to hear why it's a bad thing
>> though.
>>
>
> Because nothing else relies on this relationship in XMPP. Domain names -
> whether "subdomains" or not - do not have any relationship, implied or
> otherwise.
>
> So in order to mandate this, you really need to come up with an
> overwhelming reason why this specification should require this, unlike
> every other XMPP specification.
>

Ok. I'll see what I can do to remove that stipulation from the text. AFAIK
it won't make any technical difference, it's just a logical thing.


> >  > 5) 6.1 - if you want to rely on presence here, isn’t an unavailable
>>>>> presence the best way to signal unavailability? I don’t think it’s covered
>>>>> what receiving unavailable would mean here at the moment.
>>>>> > >
>>>>> > > See above.
>>>>> >
>>>>> > I think at least the second part of the question stands - what does
>>>>> receiving unavailable mean?
>>>>> >
>>>>> > Means that the client has gone offline and will not interact with
>>>>> the calls under its control any more. The Rayo server may choose to hang up
>>>>> those calls, wait for the client to come back, or any other
>>>>> implementation-specific behaviour.
>>>>>
>>>>> It seems worth mentioning this, to me.
>>>>>
>>>>> > > 8) 6.2.1 How does the client discover the available URI schemes
>>>>> for to/from?
>>>>> > >
>>>>> > > No such discovery is specified, and it is assumed that a Rayo
>>>>> service would document this.
>>>>> >
>>>>> > It’s not clear to me what this means for interoperability. Does it
>>>>> mean that one can’t implement a Rayo client using this XEP and expect it to
>>>>> interoperate with an arbitrary Rayo service, because it won’t know what the
>>>>> available URI schemes are?
>>>>> >
>>>>> > Even if this were available via Disco, it would make no difference.
>>>>> You couldn't build your app to compensate. I think
>>>>> per-implementation/service documentation is sufficient here.
>>>>>
>>>>> Doesn’t that mean that one can’t implement a Rayo client without
>>>>> reference to per-server documentation?
>>>>>
>>>>
>>>> One could certainly implement a client library/framework, and we have
>>>> done. When one builds / deploys an application, however, one must know
>>>> something about the server implementation. I maintain, though, that Disco
>>>> as documentation is no better than normal documentation. I'd love to hear
>>>> your argument for Disco being useful here, but it sounds like we're just
>>>> trying to tick a "haz Disco" checkbox for no reason.
>>>>
>>>>
>>>
>>> I'd expect a generically built client to be possible, and I would expect
>>> a baseline that ensured it did the basics if at all possible.
>>>
>>
>> I think the best we could do right now is "must support sip:". But then
>> someone will come along and say "what about Jingle?". Then we'll have a
>> fight over it where the IVR implementations don't give a crap about Jingle
>> and the XSF demands support for it and doesn't care about SIP
>> and...deadlock.
>>
>>
>
> I've no objection to stipulating a baseline of SIP if that's what the
> market needs.
>

Then I'll do that and pray that your position is representative of the XSF
Council. If it's not, then I'd love to hear so soon because that is a fight
no-one will win and it'd be better for me to just retract the spec.


> If this isn't possible, I'd like to know why not - I've only seen this
>>> with Jingle video calling in the past due to the intersection of deployment
>>> and patents.
>>>
>>> I would have thought that some mechanism for discovering what URI
>>> schemes were possible would be both possible and useful.
>>>
>>
>> Possible, sure. Useful...for what?
>>
>
> Since otherwise it's not clear when you get a client that it'll work (or
> not) with your server.
>

I still cannot imagine what I, as someone who has built Rayo applications
for the last 3 years, would use this for. I'd appreciate someone
contributing this part to the spec if they have a use for it.


> > > 10) 6.2.1.1 Use of presence for sending of notifications like this
>>>>> seems off. I realise this boat may have sailed, but it doesn’t seem right
>>>>> to me.
>>>>> > >
>>>>> > > We had this discussion during the Last Call, and the only
>>>>> alternative that was presented was a dependency on PubSub, against which I
>>>>> believe I presented a solid argument previously.
>>>>> >
>>>>> > I’m not exactly ignoring this comment, but I don’t have a sensible
>>>>> reply either.
>>>>> >
>>>>> > > 16) 6.3 The identifier for calls here is always a JID, isn’t it?
>>>>> If that’s the case, it’d make more sense to be using JIDs here, instead of
>>>>> adding the layer of indirection of a URI with a fixed scheme.
>>>>> > >
>>>>> > > A call URI will not necessarily always be a JID. It has been the
>>>>> intention since the start of this spec to leave open the option of other
>>>>> transports for Rayo, such as HTTP.
>>>>> >
>>>>> > In such a case, how will an entity know about the available schemes,
>>>>> and connect to them? If the implication is that there will need to be
>>>>> changes later to express how to interoperate with future systems, it
>>>>> suggests it wouldn’t be appropriate to push to Draft now with those changes
>>>>> pending.
>>>>> >
>>>>> > Any such behaviour is very much a future concern; no-one has given
>>>>> it any solid thought yet. Simply remaining generic in using URIs rather
>>>>> than protocol-specific addresses seems harmless to me, though.
>>>>>
>>>>> Possibly harmless, but it’s what it implies that might be troublesome.
>>>>> Pushing to Draft now with the expectation that new URI schemes that require
>>>>> changes to the spec will be produced later wouldn’t be appropriate.
>>>>>
>>>>
>>>> So we just stay Experimental until someone explicitly declares they
>>>> will never pursue any changes come what may?
>>>>
>>>>
>>>
>>> No, but Draft status implies that at least specific changes are not
>>> anticipated, and that any changes are going to be avoided, backwards
>>> compatible if at all possible, and are certainly gated through Council
>>> approval.
>>>
>>> So I'd expect here that even if new schemes were able to be added,
>>> there'd be a baseline and ideally a discovery mechanism.
>>>
>>>
>>>> > > 17) 6.3 I think here we’re getting into the territory where
>>>>> presence stanzas are really not inappropriate for this
>>>>> > >
>>>>> > > Do you have an alternative suggestion, or a concrete argument
>>>>> against?
>>>>> >
>>>>> > I’d have thought that (for this case) just sending the message
>>>>> (probably as headline?) would be more appropriate? This seems to be trying
>>>>> to send what is logically a ‘joined’ message to the client, rather than an
>>>>> update of presence. Presence is generally the current state of an entity.
>>>>> If you use presence for ‘joined’ and you first joined A and then joined B,
>>>>> and so the most recent presence you received had ‘joined B’ in it, it
>>>>> implies under the usual XMPP semantics that your new presence has replaced
>>>>> the old one, and thus you’re no longer joined to A.
>>>>> >
>>>>> > That's the first practical argument against the use of presence here
>>>>> that I've heard so-far; thank you. I'll give it more consideration and
>>>>> either propose a modification to the spec or produce a counter-argument.
>>>>> >
>>>>> > > 23) Example 44: This introduces ‘active speaker detection’, but
>>>>> doesn’t explain what this is (or reference an explanation), I think.
>>>>> > >
>>>>> > > It is what it says on the can, and is a common feature of media
>>>>> servers.
>>>>> >
>>>>> > Alright. I feel a bit uncomfortable introducing terms that I
>>>>> wouldn’t expect a typical XEP implementor to understand, but maybe it’s
>>>>> alright in this case.
>>>>> >
>>>>> > I highly doubt a "typical XEP implementor" would be interested in
>>>>> implementing a fully compliant Rayo server unless they were also a member
>>>>> of the set of people who had heard that term before. See later points for
>>>>> more.
>>>>>
>>>>> Well, rather the point of publishing as XEPs is that other people
>>>>> /can/ come along and implement it. Will comment more on later points when I
>>>>> get to them, I expect.
>>>>>
>>>>>
>>>
>>> FWIW, I agree with Ben here. If Active Speaker Detection is a term of
>>> art within the field, it seems like prerequisite knowledge. A reference
>>> would be nice, but aside from knowing it means detecting which entity on
>>> the call is currently speaking, I'm not sure what it would provide.
>>>
>>>
>>>> > > 33) 6.5.4 - How is discovery of the optional/extensible mechanisms
>>>>> discovered?
>>>>> > >
>>>>> > > It's not. Server documentation only.
>>>>> >
>>>>> > If it’s not discoverable, how would a client written without
>>>>> reference to a particular server’s documentation interoperate with it?
>>>>> >
>>>>> > It would not, and it could not reasonably hope to. I see no benefit
>>>>> to discovery here; it wouldn't change the situation any.
>>>>>
>>>>> I’d like to be sure I understand this, because it seems somewhat
>>>>> important. Do you mean that following XEP-0327 is not sufficient to
>>>>> implement a Rayo Client (or server)?
>>>>>
>>>>
>>>> Please explain how Disco would make any difference.
>>>>
>>>>
>>>
>>> It's not specifically disco, any discovery mechanism would do.
>>>
>>> If I have implemented a Rayo client, how does it know whether the server
>>> it's using will support its required and/or supported mechanisms?
>>>
>>
>> And my counter-point: once it discovered such information, what would the
>> client do with it?
>>
>
> We could just pretend that I have a general dislike of things which
> *could* be discoverable but aren't.
>
> But in practical terms, you seem to be insisting that a client is
> something written specifically for a particular server.
>
> In which case what good is it doing to put this specification through the
> XSF?
>

Any client library or framework (see Adhearsion/Punchblock for precedent)
would not benefit in and of itself from any such discovery, much the same
way a generic XMPP library would not. An application based on those
libraries would use certain features of the specifications which impact the
choice of server implementations they have.

If a specific group chat application was looking for an XMPP server, it
would have to (components aside) choose one which implements the
server-side parts of MUC) for example. If a MUC-specific client application
was used against a server which does not implement MUC, then the best it
could hope to do is fail to launch saying "get a better server".

Is your point about failing fast vs attempting to process a call and
failing mid-way, in a case where one deploys against an insufficient
server? Either way, one would get a usable error.


> > > 35) 6.5.4.4 - When would the nomatch expect to be triggered?
>>>>> Presumably it’s not firing off e.g. whenever anyone says anything that
>>>>> isn’t a DMTF when a DMTF input is configured? Can it trigger multiple
>>>>> times, or is it removed after a match?
>>>>> > >
>>>>> > > A nomatch event would trigger in such circumstances that input is
>>>>> received which does not match a grammar. Input for a particular modality
>>>>> (eg speech or DTMF) is not received by a recognizer unless a grammar is
>>>>> specified for that modality. A nomatch is not a standalone Rayo event, but
>>>>> delivered as a completion event reason, and as such can only be fired once
>>>>> for a given component.
>>>>> > >
>>>>> > > These semantics are standard for speech recognizers and do not
>>>>> warrant specification in Rayo beyond what is already written.
>>>>> >
>>>>> > I’m not (yet) convinced that that’s true - one should really be able
>>>>> to implement a XEP without needing implicit knowledge of how it should be
>>>>> implemented. I think I could write a compliant implementation as things
>>>>> stand that is very much not what you expect, so tightening this up seems
>>>>> sensible to me. Others may disagree.
>>>>> >
>>>>> > I disagree that one could expect this XEP to contain a recipe for an
>>>>> implementation. If it were to attempt to it would run to many volumes. This
>>>>> specification is not a typical small add-on to an IM scenario.
>>>>> >
>>>>> > > 36) 6.5.5 - I think the rules for what happens to the output when
>>>>> input begins aren’t defined. Although it’s implied that the output stops,
>>>>> does it continue again after input?
>>>>> > >
>>>>> > > No, this is specified as barge in behaviour, which is well
>>>>> understood in the field of IVR, and as such does not warrant
>>>>> re-specification in Rayo.
>>>>> >
>>>>> > I think the same holds true here as does for the previous point.
>>>>> >
>>>>> > The point about "active speaker detection" holds here. If one is not
>>>>> familiar with the term "barge in" and what happens in such a scenario as is
>>>>> widely understood in the field, then one would not be successful in
>>>>> building a useful implementation of a Rayo server.
>>>>> >
>>>>> > At some point the specification of the protocol has to give way to
>>>>> what is considered prevailing knowledge, much like MAM does not contain
>>>>> details of how to implement a database.
>>>>>
>>>>> Well, MAM doesn’t detail how to implement a database (and one need not
>>>>> use a database to implement MAM), but if there are points where one would
>>>>> need to understand how to implement a database in order to implement MAM,
>>>>> that seems like a shortcoming in MAM (Although saying that, I think one
>>>>> might reasonably argue that ‘a database’ is pretty much universal as a
>>>>> concept amongst devs (or, indeed, the general populace), while barge-in in
>>>>> this sense is not).
>>>>>
>>>>
>>>> It is universal among people who have an interest in this specification.
>>>>
>>>
>>> Unfortunately it's also a really hard term to find via Google.
>>>
>>> Maybe a sentence of explanation might help:
>>>
>>> "Prompt is a convenience component to wrap input and output components,
>>> combine their lifecycles, and allow input to barge-in on an output
>>> component in the standard sense - that is, it allows additional callers to
>>> join an active call uninvited using a special authorization."
>>>
>>
>> Ok, so I see there's some mis-understanding. Barge-in is, in a prompt
>> situation, where one interrupts the output by providing early input. Think
>> calling Fedex and not wanting to wait to hear the menu before mashing 0 to
>> get a human. You just "barged" the output part of the prompt, which
>> terminated as soon as you began providing input.
>>
>>
>
> OK, so in that case I think you need an explanation in the text, since
> that term of art seems to be used in multiple ways in the industry, and
> isn't, as you suggested, "universal".
>

I will add a brief explanation for disambiguation.


> > > 41) 6.6.2 - if the client can’t handle the call, what’re the other
>>>>> options than rejecting it? (MAY)
>>>>> > >
>>>>> > > It may simply ignore the offer and allow it to be accepted by
>>>>> another PCP.
>>>>> >
>>>>> > Does that mean that this is effectively “MUST either reject the
>>>>> call, or ignore the offer to allow it to be accepted by another PCP”?
>>>>> >
>>>>> > Sure, but it seems odd to me that we would specify that a client
>>>>> MUST not take any action on a received stanza. Is that really
>>>>> necessary/desirable?
>>>>>
>>>>> “MAY reject it, or MAY ignore it” would work fine for me too, without
>>>>> a MUST.
>>>>>
>>>>>
>>> I'd personally be more interested in knowing what the semantics of
>>> rejection are.
>>>
>>> Does rejection mean the call request is terminated, whereas ignoring it
>>> means the call request continues?
>>>
>>
>> Yes. I'll make a note to flesh this out.
>>
>>
>>> Does the text above Example 84 refer to the call already being accepted
>>> by this client, or another?
>>>
>>
>> Examples 83 and 84 are alternative responses to example 82.
>>
>>
>>> >
>>>>> > > 42) 6.8.1 - is feature-not-implemented an odd error to use for a
>>>>> protocol violation?
>>>>> > >
>>>>> > > What would be the appropriate error to use here?
>>>>> >
>>>>> > bad-request is probably closer:
>>>>> >
>>>>> > "The sender has sent a stanza containing XML that does not conform to
>>>>> >    the appropriate schema or that cannot be processed (e.g., an IQ
>>>>> >    stanza that includes an unrecognized value of the 'type'
>>>>> attribute,
>>>>> >    or an element that is qualified by a recognized namespace but that
>>>>> >    violates the defined syntax for the element); the associated error
>>>>> >    type SHOULD be "modify”.”
>>>>> >
>>>>> > whereas feature-not-implemented would be:
>>>>> > " The feature represented in the XML stanza is not implemented by the
>>>>> >    intended recipient or an intermediate server and therefore the
>>>>> stanza
>>>>> >    cannot be processed (e.g., the entity understands the namespace
>>>>> but
>>>>> >    does not recognize the element name); the associated error type
>>>>> >    SHOULD be "cancel" or "modify”.”
>>>>> >
>>>>> > This distinction is exactly why I chose feature-not-implemented. An
>>>>> "unrecognized value of the type attribute" or other such bad-request would
>>>>> look like this:
>>>>> >
>>>>> > <message type="dog"/>
>>>>> >
>>>>> > The protocol violation here would be of 6121, which this example
>>>>> (6.8.1) does not violate.
>>>>>
>>>>> 327 says that anything other than ‘normal’ is illegal, doesn’t it?
>>>>> It’s that rule that would be violated, making me suggest bad-format.
>>>>>
>>>>> > Further precedent at
>>>>> http://xmpp.org/extensions/xep-0045.html#reservednick and likely
>>>>> elsewhere.
>>>>>
>>>>> I don’t think that’s a similar situation - that’s showing what a
>>>>> server that chooses not to implement an optional feature returns if a
>>>>> client tries to use it. The case in point here is how the server responds
>>>>> to a client sending something that it cannot possibly understand, because
>>>>> the protocol isn’t allowed?
>>>>>
>>>>
>>>> No. This is exactly the same situation. This is an optional feature of
>>>> the Rayo spec.
>>>>
>>>>
>>>
>>> Well, XEP-0327 as written says servers MUST reject the traffic, so
>>> clients cannot possibly expect this to succeed.
>>>
>>
>> I don't follow. Where does it say that?
>>
>
> "If a message is directed to the call's JID with a type other than
> 'normal' then the server MUST return a <feature-not-implemented/> error"
>
> That's not optional.
>

The discussion here is wether sending messages of any type at all is
required. It is not required for a Rayo server to implement any message
stanza to a call. It is possible to implement messages of type 'normal'.
I'm not sure how I can make this any clearer; it makes perfect sense to me
and I'm failing to understand why it's not making sense to other people.

I'm really sorry, but I think we're at an impasse. I'm convinced that what
is written is correct and that the comments against it are a
misunderstanding, but I cannot think of a way to say it that removes the
misunderstanding.


>
>>
>>> There's no optional behaviour here. As such, this isn't an unimplemented
>>> feature, but a bad request.
>>>
>>> This isn't a hill for me to die on, though.
>>>
>>> Dave.
>>>
>>
>>
>
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