One of the best things that could happen today I think is Google open sourcing the Hangouts protocol. It's a reasonable alternative to XMPP and has a massive userbase. The clients are pretty horrible but that might be completely unrelated to how good the protocol is (Note: I have no idea how good it is. Because it's closed source.).
I was hopeful for a while but I don't really see it happening anymore :( Oh well...
Edit: Oh and the worst part: Communication is just one side of that coin. The other side is identity and it's one hell of a side. OpenID was a disaster. Mozilla got it mostly right with Persona but completely botched the marketing and has all but given up on it now. There is no decent foss protocol for identity/authentication today other than Persona, and nobody is working on one. There was a time indeed where I could've pictured Google working on solving this just for the hell of it. Just because it would improve the world. That Google is gone, and there's nobody with the appropriate reach that seems willing to do it now.
I've worked with all three. The H.323 vs SIP battle was fought a long time ago... for better or worse, SIP won. Any H.323 systems still in the wild can probably be considered "legacy."
That being said, while H.323 has more "batteries included," its call flow is accordingly more complex. SIP is not too bad, there is some subtlety to it, but the main issue is that you have to piece together dozens of RFCs for an interoperable system, not to speak of implementation-specific quirks.
XMPP is the more appropriate protocol in this context -- IM and group chat -- because it has had presence and ad-hoc messaging baked in from the start, including reasonably supported MUC. Ultimately, XMPP's issues are similar to SIP's -- the patchwork of XEPs is too unwieldy to work with. For an example, compare the multimedia bits (eg, Jingle) and the corresponding SIP session setup flow. The stigma of being a XML-based protocol designed in the 90's doesn't help, either.
The biggest reason SIP is sticking around, however, is that it has major buy-in from the telcos with IMS/4G. However, SIP is also a more appropriate protocol for traditional telephony. In that respect, comparing SIP and XMPP is a bit like comparing apples to oranges. With the appropriate extensions, one could behave like the other, but it wouldn't be their strength.
It seems obvious multimedia calls is part of our future, and I refuse to let that be dictated by corporate lock-in -- be that Skype/Lync, Hangouts or whatever Facebook will launch when they enable videochat. And any videochat/conference needs text messaging/conversations too, so it seems like it would be nice to run everything through one server/service.
Which I had hoped made sense would be a h.323 server (along with open source clients+maybe a websocket/web-client bridge).
Guess it'll have to be SIP for phone (so I can ditch my regular cell service), maybe SIP for videochat (but I'm sceptical about the videoconferencing bit)... and XMPP for messaging.
As neither Facebook, Google nor Microsoft support either XMPP in general (making it feasible to set up a bridge server) anymore, nor federation (which would actually be useful), I suppose I'll just have to give up on the idea that there'll appear a chat network where I'll be able to reach most of my contacts with a Free/Open client that isn't forced to play catchup to corporate whims.
For a while, Facebook via XMPP worked (but not group chat), now it's back to sms. Which is annoying because sms is gated by the telcos, although it should be easy enough to make a xmpp<>sms gateway (eg: [s]) with a spare android phone. For personal use that wouldn't have to incur any sms fees (but would mean keeping a non-free cellular plan).
For others frustrated by the same, there's at least a "traditional" project to reverse-engineer working with FBs current chat: https://github.com/jgeboski/bitlbee-facebook
[s] http://projectmaxs.org/homepage/
[ed: Forgot to commend duckduckgo and fastmail on hosting proper XMPP with federation and registration (at least ddg[d]) enabled. That's one reason why XMPP is nice -- you can actually point non-technical users at a suitable client, and add a couple of screenshots how how to set it up with ddg -- and they can then federate/talk away (that is assuming you don't/can't/won't support registration on your own server -- in my case the main reason not to recommend people wanting to talk to me to register on my server, is that I wouldn't know what kind of "SLA" my own server would have -- so if they used XMPP for other things than talking to me, having an account with someone a little more dedicated to keeping a server open to the general public might be better. But the main point is that that just works with XMPP today. And it should've just worked with both Facebook chat and Google talk/hangouts/newnamehere. And it probably also should've worked with Microsoft accounts/skype/hotmail.
[d] https://duck.co/blog/post/2/using-pidgin-with-xmpp-jabber
]
SIP was adopted by 3GPP in 1999 to be used in the mobile networks. Of course, that trickled throughout the telcos, so it now is widely used in the telco space. H.323 was widely used for PSTN backhauling to reduce tolls. However, SIP is more prevalent there, I'd guess.
Enterprise networks still use both H.323 and SIP, with more desk phones using SIP and videoconferencing equipment split, but moving to SIP.
That said, any move to SIP these days is only because there is nothing better. WebRTC is the next big thing. It borrows SDP from SIP, but no signaling protocol is defined.
Personally, I'd like to realize the vision behind what was intended to be H.325, which was to be a JSON-based signalling protocol that is fully distributed. Each application could implement whatever protocol it wanted, and they would all be associated through H.325, giving the user the feeling that these different applications work closely together. That would be possible, even when applications run on different devices.
Alas, there seems to be no financial motivator for those that control the market to explore that concept, so we're stuck with H.323, SIP, and WebRTC (and various proprietary glue pieces). The trend these days seems to be toward proprietary solutions, providing limited interop with others through SIP. Limited, as in nothing but basic voice and video.
QUIC looks interesting, but a) is very concentrated on being a transport for http/2, b) is in flux, and c) Google apparently haven't donated any code that makes sense for production (excepting client-side in Chromium).
DTLS is closely connected with WebRTC, has several implementations (though, apparently no support in Erlang/Elixir yet?) and given the current push behind WebRTC appears to be here to stay.
Honestly, I don't know how interesting "hardware phones" are anymore. As long as one can get something to work over wlan with android, things "should" be real-world deployable. And I don't have 100s of SIP devices, so I don't need to care ;-).
It may turn out that wlan+android+WebRTC+DTLS never achieves the kind of latency needed for good live video/audio... I haven't experimented that much, but hopefully it's "good enough".
At any rate, appears that SIP really is the only interop that currently works. At first glance it does seem a little complex for the use-case of text messages, inconvenient in terms of addressing -- but maybe a core focused on WebRTC/IPv6 with gateways for SIP the way to go.
Either way, I guess as long as no big players want interop, it doesn't really matter. One'll just have to make a solution that works for inter-org/inter-friends communication, with the option to federate with those interesting in joining/building a new network. Doesn't look like it'll be easy to take a bite out of FB Messenger/Google Hangouts/WhatsApp etc.
