Signaling-Concepts.md

WebRTC Experiments Signaling Concepts

This document explains inner-parts of the signaling methods used in WebRTC Experiments.

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Dynamic Channels

All "old" WebRTC Experiments require dynamic channels i.e. namespaces.

For those experiments, signaling gateway must have following features:

1. Multiplexing i.e. more than one sockets connectivity
2. Dynamic channels or namespaces

Out of multiplexing requirement; simple WebSocket implementation can't be used as signaling method in "old" WebRTC Experiments.

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A sample socket.io implementation

var io = require('socket.io').listen(app);
io.sockets.on('connection', function (socket) {
    socket.emit('connect', true);

    socket.on('message', function (data) {
        socket.broadcast.emit('message', data);
    });
});

Node.js server is expected to fire two events:

1. connect which is used to understand whether socket.io connection is opened
2. message which is used to get transmitted messages

Node.js must catch messages passed from client-side and broadcast/transmit that message over all other connected sockets.

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A full-fledge socket.io implementation / Source Code

Node.js server:

var port = 8888;

var app = require('express')(),
    server = require('http').createServer(app),
    io = require('socket.io').listen(server);

server.listen(port);

io.sockets.on('connection', function (socket) {
    if (!io.connected) io.connected = true;

    socket.on('new-channel', function (data) {
        onNewNamespace(data.channel, data.sender);
    });
});

function onNewNamespace(channel, sender) {
    io.of('/' + channel).on('connection', function (socket) {
        if (io.isConnected) {
            io.isConnected = false;
            socket.emit('connect', true);
        }

        socket.on('message', function (data) {
            if (data.sender == sender) socket.broadcast.emit('message', data.data);
        });
    });
}

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Client side:

connection.openSignalingChannel = function(config) {
   var SIGNALING_SERVER = 'http://webrtc-signaling.jit.su:80/';
   var channel = config.channel || this.channel || 'default-channel';
   var sender = Math.round(Math.random() * 60535) + 5000;
   
   io.connect(SIGNALING_SERVER).emit('new-channel', {
      channel: channel,
      sender : sender
   });
   
   var socket = io.connect(SIGNALING_SERVER + channel);
   socket.channel = channel;
   
   socket.on('connect', function () {
      if (config.callback) config.callback(socket);
   });
   
   socket.send = function (message) {
        socket.emit('message', {
            sender: sender,
            data  : message
        });
    };
   
   socket.on('message', config.onmessage);
};

All WebRTC Experiments separated signaling portion; so you can define a single method to control the entire infrastructure of WebRTC Signaling!

openSignalingChannel or openSocket are kind of those "custom" reusable methods.

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What about latest WebRTC experiments and libraries?

All latest WebRTC experiments and libraries are capable to work with each and every gateway exists in the world!

Taking node.js for instance; your server code looks like this:

io.sockets.on('connection', function (socket) {
    socket.on('message', function (data) {
        socket.broadcast.emit('message', data);
    });
});

And web-browser side code looks like this:

connection.openSignalingChannel = function(callback) {
    return io.connect().on('message', callback);
};

Want to use XHR, WebSockets, SIP, XMPP, etc. for signaling? Read this post.

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What about Firebase?

Firebase is an io-based service stores data in JSON format; considered most suitable solution for WebRTC signaling. Its APIs are easier to use and understand. Firebase supports dynamic channels too!

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What about PubNub or Pusher?

PubNub or Pusher provides APIs for realtime connection. PubNub uses wider methods and techniques.

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Expectations

All "old" WebRTC experiments expects that signaling channels must be able to send and receive messages over unique channels.

All "new" WebRTC experiments can work in any circumstance!

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Links

1. Socket.io over Node.js
2. WebSockets over Node.js

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License

WebRTC Experiments are released under MIT licence . Copyright (c) 2013 Muaz Khan.