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HTML5 Web Socket in Essence

 
Written by Wayne Ye  Friday, June 10, 2011

HTML5 WebSocket defines a bi-directional, full-duplex communication channel operates through a single TCP connection, this article discusses its fantastic performance, the WebSocket protocol principle and its handshake mechanism, and develop a WebSocket application in action (Team Poker).


Embeded youku video link because Youtube is outside of the largest "intranet" in the entire universe!!

Table of Content

  1. Introduction
  2. Background
  3. WebSocket In Essence
  4. Experimental Demos
  5. Browser Support
  6. WebSocket JavaScript API
  7. Develop WebSocket In Action - Team Poker
  8. Open Issues
  9. Conclusion
  10. References & Resources 

Introduction

HTML5 WebSocket defines a bi-directional, full-duplex communication channel that operates through a single TCP socket over the Web, it provides efficient, low-latency and low cost connection between web client and server, based on WebSocket, developers can build scalablereal-time web applications in the future. Section below is the official definition of WebSocket copied from IETF WebSocket protocol page: 

The WebSocket protocol enables two-way communication between a user agent running untrusted code running in a controlled environment to a remote host that has opted-in to communications from that code.  The security model used for this is the Origin-based security model commonly used by Web browsers.  The protocol consists of an initial handshake followed by basic message framing, layered over TCP.  The goal of this technology is to provide a mechanism for browser-based applications that need two-way communication with servers that does not rely on opening multiple HTTP connections (e.g. using XMLHttpRequest or <iframe>s and long polling).

This article is trying to go through WebSocket basic concept, the problems it is going to solve, explain it in essence, watch some experimental Demos, develop a simple WebSocket application in action (Team Poker), and describe current open issues of WebSocket. I sincerely hope it will be systematicallyeasy to understandfrom surface to deep so that eventually readers would not only learn what WebSocket is from high level but also understand it in depth! Any thoughts, suggestions or criticism you may have after reading this article will help me to improve in the future, i would appreciate it if you could leave a comment.

Background

In traditional web applications, in order to achieve some real-time interaction with server, developers had to employ several tricky ways such as Ajax pollingComet (A.K.A Ajax push, Full Duplex Ajax, HTTP Streaming, etc.), those technologies either periodically fire HTTP requests to server or hold the HTTP connection with server for a long time, which "contain lots of additional, unnecessary header data and introduce latency" and resulted in "an outrageously high price tag". websocket.org explained the problems exhaustively, compared the performance of Ajax polling and WebSocket in detail, built up two simple web pages, one periodically communicated with server using traditional HTTP and the other used HTML5 WebSocket, in the testing each HTTP request/response header is approximate 871 byte, while data length of WebSocket connection is much shorter: 2 bytes after connection established, as the transfer count getting larger, the result will be:

Traditional HTTP Request 

  • Use case A: 1,000 clients polling every second: Network throughput is (871 x 1,000) = 871,000 bytes = 6,968,000 bits per second (6.6 Mbps)

  • Use case B: 10,000 clients polling every second: Network throughput is (871 x 10,000) = 8,710,000 bytes = 69,680,000 bits per second (66 Mbps)

  • Use case C: 100,000 clients polling every 1 second: Network throughput is (871 x 100,000) = 87,100,000 bytes = 696,800,000 bits per second (665 Mbps)

HTML5 WebSocket

  • Use case A: 1,000 clients receive 1 message per second: Network throughput is (2 x 1,000) = 2,000 bytes = 16,000 bits per second (0.015 Mbps)

  • Use case B: 10,000 clients receive 1 message per second: Network throughput is (2 x 10,000) = 20,000 bytes = 160,000 bits per second (0.153 Kbps)

  • Use case C: 100,000 clients receive 1 message per second: Network throughput is (2 x 100,000) = 200,000 bytes = 1,600,000 bits per second (1.526 Kbps)

Finally a more readable diagram:

Polling VS WebSocket

 "HTML5 Web Sockets can provide a 500:1 or — depending on the size of the HTTP headers — even a 1000:1 reduction in unnecessary HTTP header traffic and 3:1 reduction in latency".  --WebSocket.org

WebSocket In Essence

The motivation of creating WebSocket is to replace polling and long polling(Comet), and endow HTML5 web application the ability of real-time communication. Browser based web application can fire WebSocket connection request through JavaScript API, and then transfer data with server over only one TCP connection.


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