What is SPDY?

  • SPDY, pronounced “SPeeDY”,  is an experimental application-layer protocol from Google developed as part of its "Let's make the web faster" initiative to help reduce the latency of web pages.  
  • This new protocol transports the existing HTTP protocol more efficiently (up to 50% faster). 
  • It is NOT a replacement for HTTP. It replaces some parts of HTTP, but mostly augments it. At the highest level of the application layer, the request-response protocol remains the same. SPDY still uses HTTP methods, headers, and other semantics. But SPDY overrides other parts of the protocol, such as connection management and data transfer formats.
  • SPDY is supported by Chrome web browser & Firefox 11 (disabled by default)
  • Amazon has baked SPDY support into its Silk browser for the Kindle.
  • Chrome SPDY indicator is a Chrome extension to visualize SPDY support in your address bar.
  • Twitter joins Google Search, Gmail in serving webpages over the SPDY protocol when available
  • SPDY may become part of HTTP 2.0
  • The problems with HTTP that SPDY tries to address are: 
    • the server cannot initiate a connection
    • headers are always uncompressed (N.B. cookies are sent in the header)
    • in a persistent connection, all headers are resent for each request
    • data is not always compressed
    • everything is in clear text       
  • SPDY addresses these issues by:
    • allowing unlimited and interleaved requests through a single connection
    • prioritizing requests (controlled by the client only)
    • compressing headers
    • allowing the server to push resources to the client without the client's asking (e.g. you're going to want the CSS file anyway)
    • allowing the server to suggest in the header what other resources the client might want to request (so no need to wait for the HTML to be parsed before knowing)
    • always using SSL

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