Communications of the ACM
Spdy: An Experimental Protocol For a Faster Web
As part of the "Let's make the web faster" initiative, we are experimenting with alternative protocols to help reduce the latency of web pages.
One of these experiments is SPDY (pronounced "SPeeDY"), an application-layer protocol for transporting content over the web, designed specifically for minimal latency. In addition to a specification of the protocol, we have developed a SPDY-enabled Google Chrome browser and open-source web server.
In lab tests, we have compared the performance of these applications over HTTP and SPDY, and have observed up to 64% reductions in page load times in SPDY.
We hope to engage the open source community to contribute ideas, feedback, code, and test results, to make SPDY the next-generation application protocol for a faster web.
Web Protocols and Web Latency
Today, HTTP and TCP are the protocols of the web. TCP is the generic, reliable transport protocol, providing guaranteed delivery, duplicate suppression, in-order delivery, flow control, congestion avoidance and other transport features. HTTP is the application level protocol providing basic request/response semantics. While we believe that there may be opportunities to improve latency at the transport layer, our initial investigations have focussed on the application layer, HTTP.
Unfortunately, HTTP was not particularly designed for latency.
SPDY is not the only research to make HTTP faster. There have been other proposed solutions to web latency, mostly at the level of the transport or session layer.
Goals for SPDY
The SPDY project defines and implements an application-layer protocol for the web which greatly reduces latency. The high-level goals for SPDY are:
- To target a 50% reduction in page load time. Our preliminary results have come close to this target (see below).
- To minimize deployment complexity. SPDY uses TCP as the underlying transport layer, so requires no changes to existing networking infrastructure.
- To avoid the need for any changes to content by website authors. The only changes required to support SPDY are in the client user agent and web server applications.
- To bring together like-minded parties interested in exploring protocols as a way of solving the latency problem. We hope to develop this new protocol in partnership with the open-source community and industry specialists.
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