Re: [rtcweb] My Opinion: Why I think a negotiating protocol is a Good Thing

If "negotiation protocol" means something that resembles ROAP (i.e. more 
or less a wrapper on SDP o/a that enables negotiation of 
session/streams), then I agree. I really like that the application does 
not need to bother, all knowledge of state, codecs, RTP, .... can be 
limited to the browser as long as the app passes the blobs on.

On 10/18/2011 01:43 PM, Harald Alvestrand wrote:
> (Apologies for the length of this note - but I wanted to follow this
> argument a bit deeply)
>
> In the discussions about RTCWEB signalling, I’ve had a change of heart.
> Or perhaps it’s just a change of terminology.
>
> The high bit is this:
> I believe we need to standardize a negotiation protocol as part of RTCWEB.
> This needs to be described as a protocol, and cannot usefully be
> described as an API.
>
> This note is to explain to my fellow WG members what led me to this
> conclusion, and - in some detail - what I think the words in the above
> paragraph mean.
> Those who don't want to read a long message can stop here.
> ----------------------------------------------------------------------------
>
> The context of RTCWEB is the well known trapezoid:
>
> +-----------+ +-----------+
> | Web | | Web |
> | | Signalling | |
> | |-------------| |
> | Server | path | Server |
> | | | |
> +-----------+ +-----------+
> / \
> / \ Proprietary over
> / \ HTTP/Websockets
> / \
> / Proprietary over \
> / HTTP/Websockets \
> / \
> +-----------+ +-----------+
> |JS/HTML/CSS| |JS/HTML/CSS|
> +-----------+ +-----------+
> +-----------+ +-----------+
> | | | |
> | | | |
> | Browser | ------------------------- | Browser |
> | | Media path | |
> | | | |
> +-----------+ +-----------+
>
> or even the triangle, where the triangle is formed when the two Web
> severs on top are collapsed into one.
>
> A design criterion for RTCWEB has been that it should be possible to
> write applications on top of RTCWEB simply - that is, without deep
> knowledge about the world of codecs, RTP sessions and the like.
> Another design criterion is that interworking should be possible - which
> means that SOMEWHERE in the system, deep knowledge about the world of
> codecs, RTP sessions and the like must be embedded; we can’t just
> simplify our options until everything’s simple.
>
> There’s one place in the ecosystem where this knowledge HAS to be - and
> that is within the browser, the component that takes care of
> implementing the codecs, the RTP sessions and the related features. If
> we can avoid requiring embedding it twice, that’s a feature.
>
> It used to be that I was a believer in APIs - that we should make the
> API the “king”, and describe the way you generate an RTP session as “you
> turn this knob, and get this effect”.
> After looking at the problem of Web applications that don’t have domain
> knowledge for a while, I’ve concluded that this doesn’t work. There’s
> the need for one browser to communicate with the other browser, and if
> the intermediate components are to have the ability to ignore the
> details, what’s communicated has to be treated like a blob - something
> passed out of one browser’s API and into another browser’s API,
> unchanged by the application - because the application must be able to
> ignore the details.
>
> OK, now we have the API with blobs. We also have to make some
> assumptions about how those blobs are transported, who’s responsible for
> acting on them, and so on. And we have to make sure different browsers
> implement the blob the same way - that is, it has to be standardized.
> What’s more - we DO want to enable applications that are NOT simple.
> Including gateways, which are not browsers. So applications must be free
> to look inside the blob - break the blob boundary - when they need to.
> So this pulls in the same direction as the need for interoperability -
> the format, semantics and handling rules for these blobs has to be
> specified. In some detail.
>
> So we have:
> - a data format
> - a transmission path
> - a set of handling rules, in the form of states, processes and timers
>
> This doesn’t look like an API any more. This looks like a protocol.
> We’ve got experience in describing protocols - but it becomes much
> easier to apply that experience when we call it a protocol.
>
> Let’s do that.
>
> But - you did not address my point...
> ----------------------------------------------
> No, I didn’t. But here are some points that might bear watching.
>
> “We shouldn’t mandate a new protocol on the wire”.
> We’re not. We’re specifying one, and mandating it for a specific point:
> The browser/JS interface.
> We can have applications that parse it locally using a JS library; in
> that case, the protocol runs between the browser and the local JS
> application.
> We can have applications that pass the blobs to a server for gatewaying
> into something else; in that case, the protocol runs between the browser
> and the server.
> We can have applications that pass the blobs (possibly via a very simple
> server) to another browser, unchanged; in that case, the protocol runs
> between the two browsers.
>
> In no case does the browser need to know where the other end is; all it
> cares about is that the messages flow according to protocol.
>
> “We should build knobs and let JS libraries take care of what’s on top
> of them”.
> Well - we could. But it violates the idea of only having the domain
> knowledge present once.
> If you have to have a browser that implements codec A, and a JS library
> that knows how to control codec A, you are *requiring* knowledge in two
> places. That’s not optimal.
> Things may change in the future - once downloadable codecs actually
> work, downloadable negotiation blobs may be a reasonable counterpart.
> But we’re not there now.
>
> “We should use existing protocol X”
> We could. But then, we’d buy into all the baggage of protocol X - both
> the things it requires us to do and the things that it won’t let us do.
> Doesn’t sound too good to me.
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