Do Websockets Allow for P2P (Browser to Browser) Communication

Do websockets allow for p2p (browser to browser) communication?

No. Browsers can only initiate WebSockets connections, not receive them. The W3C browser API spec only defines how to start an outbound connection.

You can make an application that would both initiate and accept WebSockets connections, but browsers do not do this.

You might look at Pusher App which you could use to build a WebSockets application with multiple clients. The service provides up to 20 simultaneous WebSockets clients for free (you can pay for higher scaling).

Update:

The WebRTC protocol and API is making rapid progress and allows a Data Channel to be established between two peers (you still may need a STUN/TURN server for the initial NAT traversal and setup).

How can I make a browser to browser (peer to peer) connection?

Here on Stackoverflow are several topics about P2P connections in browsers:

Will HTML5 allow web apps to make peer-to-peer HTTP connections?
What techniques are available to do P2P in the browser?
Does HTML5 Support Peer-to-Peer (and not just WebSockets)
Can HTML5 Websockets connect 2 clients (browsers) directly without using a server (P2P)
Is it possible to create peer-to-peer connections in a web browser?
Do websockets allow for p2p (browser to browser) communication?
HTML 5 Peer to Peer Video Possibilities?
Is WebRTC implemented in any browsers yet?

As mentioned in most of the topicts, both 2008 HTML5 working drafts were having a section "Peer-to-peer connections":

http://www.w3.org/TR/2008/WD-html5-20080122/#peer-to-peer
http://www.w3.org/TR/2008/WD-html5-20080610/comms.html#peer-to-peer

Since the W3C Working Draft 12 February 2009 the section "Peer-to-peer connections" disappeared. But this P2P connection is not gone. It's back under the name PeerConnection within the WebRTC (Real-Time Communications) specifications:

http://dev.w3.org/2011/webrtc/editor/webrtc.html#peerconnection (W3C Editor's Draft)
http://www.whatwg.org/specs/web-apps/current-work/webrtc.html#peerconnection (Since 5th December 2011 forwarded to W3C Editor's Draft)

Since 31 October 2011, the W3C Editor's Draft is an official Working draft:

http://www.w3.org/TR/2011/WD-webrtc-20111027/#peerconnection

The only implementation of the PeerConnection (UDP based) exists in the modified WebKit by the Ericsson labs (May 2011), which is working quite well. Some patches are in WebKit now (Oct. 2011 -- see updates below!):

https://labs.ericsson.com/apis/web-real-time-communication/
https://labs.ericsson.com/developer-community/blog/update-webkit-contributions

Additionally, the WebRTC initiative is a project by Google, Mozilla and Opera. Thus, they are continuing the specification on PeerConnection:

http://www.webrtc.org/

Probably Chrome (uses WebKit) will be the first major browser supporting WebRTC with PeerConnection:

http://www.webrtc.org/blog/firststeptowardchromeintegration
http://groups.google.com/a/chromium.org/group/chromium-dev/browse_thread/thread/95bf1e2e1de852fc
https://lists.webkit.org/pipermail/webkit-dev/2011-November/018445.html

Since 18th January 2012, Chrome is supporting WebRTC as well. It can be uses in the Dev channel (Windows, OSX, Linux) and the Canary build (Windows and OSX) by enabling it under chrome://flags. It only only supports MediaStream like Video and audio and can be tested with several Demos. Transferring application data like String/ArrayBuffer/... is not supported until now.

Since 16th March 2012, the WebRTC Editor's Draft separates a "Peer-to-peer Data API" to send and receive generic application data (String, ArrayBuffer and Blob). Chromium wants to implement the Data API soon (10th April 2012).

On April, 3rd, Mozilla published a first working example on WebRTC for Firefox as well.

DataChannel is planned for version 25 of Chrome, behind a flag, meanwhile it can be tested in Firefox Nightly/Aurora (12th December 2012):

http://updates.html5rocks.com/2012/12/WebRTC-hits-Firefox-Android-and-iOS

2018: DataChannels are still experimental, but available in current versions of Chrome and Firefox:

https://developer.mozilla.org/en-US/docs/Web/API/RTCDataChannel

WebRTC and Websockets. Is there a difference

There's two sides to WebRTC.

JavaScript APIs (getUserMedia) that allow an app to access camera and microphone hardware. You can use this access to simply display the stream locally (perhaps applying effects), or send the stream over the network. You could send the data to your server, or you could use...
PeerConnection, an API that allows browsers to establish direct peer-to-peer socket connections. You can establish a connection directly to someone else's browser and exchange data directly. This is very useful for high-bandwidth data like video, where you don't want your server to have to deal with relaying large amounts of data.

Take a look at the demos to see both parts of WebRTC in action.

So in a nutshell:

WebSockets allow full-duplex communication between a browser and a web server.
WebRTC's PeerConnection allows full-duplex communication between two browsers.

Will HTML5 allow web apps to make peer-to-peer HTTP connections?

Instead of intelligent guesses, here is an informed answer:

HTML 5 plans to allow peer to peer connections from javascript, but these connections WILL NOT BE RAW TCP.

The complete spec can be found at http://dev.w3.org/html5/websockets/

jrh

EDIT: with specific reference to peer to peer connections, check out these links:

Regarding peer to peer connections: http://www.w3.org/TR/2008/WD-html5-20080122/#peer-to-peer
Regarding broadcast connections to the local network: http://www.w3.org/TR/2008/WD-html5-20080122/#broadcast
Regarding TCP connections (in the encoded protocol): http://www.w3.org/TR/2008/WD-html5-20080122/#tcp-connections
Complete proposed spec: http://www.w3.org/TR/2008/WD-html5-20080122/#network

Its important to note that the capabilities are still being negotiated. It will be nice to be able to create "local chat" web apps :)

jrh

Browser to browser communication without a server?

Looks like there may be hope on the horizon: http://www.w3.org/TR/webrtc/

Do Websockets Allow for P2P (Browser to Browser) Communication