- 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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