转 HTTP/2: The Long-Awaited Sequel

HTTP/2: The Long-Awaited Sequel

Thursday, October 9, 2014 2:01 AM

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Ready to speed things up?

Here at Microsoft, we’re rolling out support in Internet Explorer for the first significant rework of the Hypertext Transfer Protocol since 1999. It’s been a while, so it’s due.

While there have been lot of efforts to streamline Web architecture over the years, none have been on the scale of HTTP/2. We’ve been working hard to help develop this new, efficient and compatible standard as part of the IETF HTTPbis Working Group. It’s called, for obvious reasons, HTTP/2 – and it’s available now, built into the new Internet Explorer starting with the Windows 10 Technical Preview.

You can see an overview of the work we have been doing with the HTTPbis working group by checking out the Microsoft Open Technologies HTTP/2 page.

Why is Internet Explorer leading with HTTP/2 implementation?

Performance matters in an increasingly real-time and mobile world – even gains that may seem merely incremental make a difference. For instance a Bing study found that a 10ms increase in page load time costs the site $250K in revenue annually; a 100ms increase – that’s a third the speed of the blink of the human eye, mind you – undid three months of work that went into improving user engagement via better search results relevance. That 100ms delay in the responsiveness of a transactional web page has been shown to cost big online retailers up to 1% of sales due to search abandonment. So what this working group is doing has real economic impact.

What is wrong with what we had yesterday?

For the most part, the way a Web page gets loaded today happens pretty much the same way it did in the days of 800x600-pixel displays. Certainly the web is a faster place today, but it could be much faster and much more resource efficient.

Building a page today still requires a lot of individual queries between the browser and the server, and each individual call has to wait until the server responds before sending the next. Sure, you can open more independent, parallel connections, but this still limits how many items can be requested simultaneously. It also dictates the order of the responses and prevents the server from optimizing responses.

So how is HTTP/2 different?

HTTP/2 delivers the Web page elements quicker and more efficiently, taking advantage of all the available bandwidth. With long-lived connections and multiplexing (the protocol’s ability to combine multiple requests on one connection), more web page items arrive sooner. Experimental HTTP/2 features such as server push and request dependencies could further improve web performance in the future.

What does this mean for developers?

HTTP/2 was designed from the beginning to be backwards-compatible with HTTP/1.1. That means developers of HTTP libraries don't have to change APIs, and the developers who use those libraries won't have to change their application code. This is a huge advantage: developers can move forward without spending months bringing previous efforts up to date.

What about networks? And security?

Fewer and less frequent connections also means that HTTP/2 will put less pressure on the network – and when you consider the scale of the web today, that could significantly increase the efficiency of networks, particularly mobile ones. Given HTTP/2’s efficient connection model, the performance impact of adding TLS to a site will be lessened, opening up the opportunity for more administrators to add TLS to their sites.

When can I get it?

HTTP/2 support is in IE on the Windows 10 Technical Preview. The work on HTTP/2 for IE really began in Windows and Windows Phone 8.1 when we added the experimental SPDY 3.0 protocol. This gave us a chance to gain some experience with a multiplexing HTTP protocol and helped move us towards HTTP/2 and what will now be an industry standard.

SPDY was a good starting point for the HTTP/2 standard, but it is an experimental protocol that does not lend itself to long-term adoption. With the development of HTTP/2, we will remove support for SPDY in all future versions of IE. Web sites and applications currently using SPDY should be able to migrate to HTTP/2 with little or no changes.

How should developers and site owners prepare for the change?

• Run the Windows 10 Technical Preview version of IE
• Start up the developer tools and turn on network tracing
• Load sites that support HTTP/2 draft-14. Some great sites are listed on the per implementer pages under:https://github.com/http2/http2-spec/wiki/Implementations
• Watch the HTTP/2 packets flow

The Technical Preview has HTTP/2 server support also. This means you can create sites in IIS and test your content end to end. Note: in the Technical Preview versions of both IE and IIS, non-secure connections (i.e. HTTP) are not supported on HTTP/2; only secure connections (i.e. HTTPS) are supported on HTTP/2.

Check out our HTTP/2 implementation and put it through its paces! Let us know if you have feedback via @IEDevChat or Connect.

— Rob Trace, Senior Program Manager

— David Walp, Senior Program Manager