What is HTTP/2

The internet is in a constant process of development that is characterized by advanced technologies, new content, and growing user demands. The simpler days of simpler websites have now been replaced by complex web presences that are perfectly tailored to the visitor and their devices. Access time and data transfer play an ever-increasing role regarding the usability and speed at which modern websites display their content. It is therefore not surprising that HTTP/2 is a modern, more advanced version of the old internet protocol, HTTP/1.1, and should decrease the loading time.

When looked at from a technical perspective, every communication unit is comprised of two areas: the message header, also known as HTTP header, and the message body. The header delivers all relevant information that needs to be interpreted, such as the message body that contains the user data.

Just like the two cornerstones of the World Wide Web – URL and HTML – the development of HTTP began in the European Organization for Nuclear Research (CERN) in Switzerland - this took place in 1989. The first published specification, RFC 1945 (Request For Comments), issued in May 1996, became commonly known as HTTP/1.0. This first version was replaced in June 1999 by HTTP/1.1, which is still in use today. The official successor HTTP/2 was launched in May 2015 as RFC 7540 and the plan is for it to revolutionize data transfer online.

One of the main characteristics of HTTP/1.1 has already been mentioned: in order to transfer different page elements like image, JavaScript, or CSS files to the client/browser, a separate TCP/IP connection needs to be opened and closed again. Just like its role model, SPDY, HTTP/2 uses the multiplex procedure in order for the whole website to be loaded with just a single connection. The server also has the ability to pass on predictable follow-up data to the client without them having to ask (server push).

With HTTP/2, data packets from websites can be sent in order of their priority; for example, elements that are responsible for building the site would appear first. The HTTP/2 header is sent heavily compressed in comparison to HTTP/1.1 because unnecessary information is omitted. An additional improvement is the use of binary code (in place of text files) when communicating, which simplifies the process and makes it less error-prone.

Here is a summary of all the HTTP/2 improvements:

• connection between a browser (client) and a website
• binary-coded message exchange
• heavily compressed HTTP message header
• server push with foreseeable requests (only for Apache and not for Nginx)
• prioritization of important site elements

The background of the new HTTP/2 features is illustrated in this video by Akami Technologies:

Since the release of HTTP/2, a lot of work has been done. Numerous web browsers and servers meanwhile support the new internet protocol. Mozilla Firefox has even had the protocol implemented since version 36 (February 2015). All versions until now have been loaded with HTTP/2 over TLS, which is the encrypted variant of the transfer protocol.

The number of websites that already use the new transfer protocol is relatively low compared to supporting browsers. Nevertheless, the number increased within one year to almost 10% from 1.2% at the end of September 2016. In March 2017, at least 12.7% of all website were using HTTP/2. An overview of the current state of usage can be found here. So far website operators with very high viewing numbers, like Google and Twitter, have converted their web presence to HTTP/2. Considering the advantages and the strongly increasing support through all current browsers, it will only be a question of time until the majority of websites use HTTP/2.

This overview shows which browsers support HTTP/2:

*partially supported