Connecting Multiple Data Channels from One Peer Connection

[Wei]

Hi All:

There are two peers: peer-1 and peer-2. They both declared four variables like the following:

           var dataSendChannelA;

           var dataSendChannelB;

           var dataReceiveChannelA;

           var dataReceiveChannelB;

They both created two data channels from one peer connection like the following:

dataSendChannelA = peerConnection.createDataChannel(“channelA”, {reliable: false};

dataSendChannelB = peerConnection.createDataChannel(“channelB”, {reliable: false};

 

When peer-1 is ready to connect to the peer-2's data channels, I only know the following:

peerConnection.ondatachannel = function (event) { 

  dataReceiveChannel = event.channel;

} 

What I do not know is how to get both dataChannelA and dataChannelB connected with the corresponding peer-2's channels.  I am guessing that the “event” object should have the channel ID/label information, but I do not know how to get to it.

 

Help is greatly appreciated.

 

-wei

 

 

[Taylor Brandstetter]

The data channel has a "label" attribute you can read. Or you can just negotiate the channels out-of-band, assigning IDs directly such that they match up on each side:

dataChannelA = peerConnection.createDataChannel(“channelA”, {negotiated: true, id: 1};

dataChannelB = peerConnection.createDataChannel(“channelB”, {negotiated: true, id: 2};

Then you won't even need to use the "datachannel" event. You can just wait for the readyState to reach "open".

By the way, "reliable: false" will not have any effect. If you want an unreliable channel, you must use either "maxRetransmitTime" (renamed to "maxPacketLifeTime" in the spec, but not yet in Chrome) or "maxRetransmits".

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[Wei]

Taylor,

Thank you very much for the pointer. If I use "negotiated" as you suggested in peer-1,  how would I handle the auto-negotiation and readyState === "open" in peer-2?  How are the auto-negotiation and  testing readyState related to peer Connection's "ondatachannel" event? Would appreciate a sample code snippet.

-wei,

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[Taylor Brandstetter]

To use "negotiated", you would just call "createDataChannel" on both peers, with the same arguments.

ID negotiated in-band:

// On peer 1:

channel = pc.createDataChannel("label");

// On peer 2:

pc.ondatachannel = function (event) { 

  channel = event.channel;

}

ID negotiated out-of-band:

// On peer 1:

channel = pc.createDataChannel("label", {negotiated: true, id: 1});

// On peer 2:

channel = pc.createDataChannel("label", {negotiated: true, id: 1});

My point about waiting for "readyState" to be "open" is just that you can't send data until it is. That applies in both cases.

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[Wei]

Taylor,

Thank you very much.  You have been a great help.

-wei,