HTTP/2 is coming. What does this mean for SEO?

HTTP has been around over 15 years and is showing it’s age. The demands of page loading have increased exponentially, with statistics showing that over 50% of websites load 75 or more files. This is currently difficult to achieve, since HTTP/1.1 only allows one request per TCP connection. To work around this problem, browsers have been issuing parallel requests for multiple TCP connections, but if too many are made it becomes counter-productive with impaired performance, since data ‘on the wire’ is duplicated.

The Internet Engineering Task Force (IETF) have been developing HTTP/2 after Google’s SPDY started showing significant improvements over HTTP/1.1.

The benefits of HTTP/2 include:

  • Header compression – the header size is vastly reduced.
  • Multiplexing and concurrency – multiple requests can be sent in quick succession over a TCP connection, with the ability to receive responses out of order, thereby eliminating the requirement for multiple connections between server and client.
  • Server push – the server’s able to send resources not yet requested by the client.
  • Stream dependencies – the server can receive a message from the client showing the most important elements.
  • Prioritisation – dependency levels are assigned to requests, which can be used by the server to speed up delivery of higher priority resources.
  • Binary – HTTP/2 is more compact and less error-proneis so easier for a server to parse, with no additional time wasted converting information from text to binary (the native computing language).

HTTP/2 itself supports both secure and non-secure connections. However, some browsers, e.g. Mozilla Firefox and Google Chrome will only support HTTP/2 over a secure connection. This means that to take advantage of HTTP/2 sites will need to be secure. With new initiatives afoot, free security certificates for websites aren’t hard to come by.

As for the question concerning HTTP/2 impacting on SEO, Google Webmaster Trends Analyst, John Mueller, said that HTTP/2 will be recognised by Googlebot very soon. Google will probably be adding more indicators of user experience to their algorithms in the future and the important point to note is that HTTP/2 is faster, providing a better user experience. Google have included speed as a ranking factor and it will be interesting to see how much additional importance will be placed on the added speed, as well as if HTTP/2 itself becomes a ranking factor.

The IETF is expected to standardise Google’s QUIC (Jim Roskind’s transport layer network protocol) fairly soon. QUIC supports multiplexed connections over the connectionless UDP, rather than on top of TCP, used by SPDY and HTTP/2. QUIC brings the same benefits as these two, but with a difference, since there’s no head‑of‑line blocking. Delaying just one packet of data pauses the many SPDY streams. Since TCP only provides a single serialised stream interface, HTTP/2 streams to pause, but with QUIC, if a single packet’s dropped, there’s only a delay to one stream. Many people aren’t aware that Google uses QUIC for services like YouTube. Users on Chrome have reported 30% less buffering.

Like QUIC, Akamai’s replacement for TCP known as Giga also averages a 30% increase in speed, with reports from some countries (e.g. India and China) indicating a 150% speed increase. Giga can determine when a connection still has a capacity, so it’s better for connection paths and detecting when packets are dropped, quickly sending them again.

HTTP/2 is currently on draft 14 and will probably be finalised this year. At present, few SEO companies appear to be supporting HTTP/2 but upgrading’s as simple as updating server software. If a browser doesn’t support HTTP/2, it will simply downgrade the connection to HTTP/1.1. Even if search rankings aren’t improved just yet, the additional speed will be great for users and it’s highly likely to improve conversion rates.


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