Creating DataChannel that sends data over SCTP instead of RTP

Question

I am trying to create a file sharing site using WebRTC.

My testing environment:

Chrome Canary 42.0.2275.0 Mac 10.10 (14A389)

Code:

var arrayToStoreChunks = [];
channel.onmessage = function(data){
  // console.log(data.data);
  var data = data.data;

  arrayToStoreChunks.push(data.message); // pushing chunks in array

  if (data.last) {
    downloadURI(arrayToStoreChunks.join(''), 'some.jpg');
    arrayToStoreChunks = []; // resetting array
  }
};

var button = document.getElementById('button');
var fileElement = document.getElementById('files');
button.onclick = function(){
  var reader = new FileReader()
  reader.readAsDataURL(fileElement.files[0])
  reader.onload = onReadAsDataURL;
};

function downloadURI(uri, name) {
  var link = document.createElement("a");
  link.download = name;
  link.href = uri;
  link.click();
}

var chunkLength = 1000;
function onReadAsDataURL(event, text) {
  var data = {}; // data object to transmit over data channel

  if (event) {
    text = event.target.result;
  }

  if (text.length > chunkLength) {
    data.message = text.slice(0, chunkLength);
  } else {
    data.message = text;
    data.last = true;
  }

  channel.send(data);

  var remainingDataURL = text.slice(data.message.length);
  if (remainingDataURL.length) {
    setTimeout(function () {
      onReadAsDataURL(null, remainingDataURL); // continue transmitting
    }, 500);
  }
}

I am chunking the data and sending at whatever size per message with whatever delay I specify. This works when I have the var optionalRtpDataChannels = {optional: [{'RtpDataChannels': true}]}; and pass that object into new RTCPeerConnection(servers, optionalRtpDataChannels);. However, this is too slow for a file sharing web app and I would like to use WebRTC DataChannels to do this.

I tried what was suggested on this SO answer Send image data over RTC Data Channel with no luck. It suggests that if I leave out the RtpDataChannels: true option that data.send() will be throttled to 64KB/s as opposed to 3KB/s(confirmed by my testing) which is what RTP is throttled to.

Any ideas on how I can send larger files over a DataChannel faster than 3KB/s?

did you check sharefest.me and peerjs code? My understanding is that they already do this, and their code is open sour, provided under a permissive license. — Dr. Alex Gouaillard, Jan 14 '15 at 05:42
@AlexGouaillard sharefest doesn't seem to be working at the moment — javascriptttt, Jan 15 '15 at 22:41
IT's possible, I have not look dat their code for long. they were the pioneer of the data channel, especially regarding the bandwidth benchmark. I think they went on another higher level project: peer5.com — Dr. Alex Gouaillard, Jan 16 '15 at 04:35

score 1 · Answer 1 · answered Jan 20 '15 at 16:57

You're sending (as best I can tell) one chunk per 500ms. That's where your primary limitation is, I think.

In firefox, you can just call .send() for every chunk with no (or minimal) delay. They will queue and go out as fast as possible. Note this does take memory, though holding the data in remainingDataURL would take memory as well.

Fancier methods could monitor the amount of buffered data, that might avoid problems if Chrome won't let you send all the data at once (it should...)

Creating DataChannel that sends data over SCTP instead of RTP

1 Answers1