HTTP/3 and QUIC FAQ

HTTP/3 is the newest version of the Hypertext Transfer Protocol, formerly referred to as "HTTP over QUIC," and is the successor to HTTP/2.

QUIC was originally a Google effort to improve HTTP/2 by transporting it encrypted over UDP. In 2016, the IETF began working to standardize the protocol. Part of that process involved splitting QUIC into the transport protocol (QUIC) and the application protocol (HTTP/3).

HTTP/3 is close to its final form. The IETF drafts are going through the last formalities before being published as RFCs.

The main difference is HTTP/3 uses QUIC, which is is built on UDP, while HTTP/2 uses TCP. In addition, HTTP/3 uses QPACK to compress headers, while HTTP/2 uses HPACK to compress headers.

No. HTTP/2 and HTTP/3 work in a similar way, but HTTP/2 uses TCP, while HTTP/3 uses UDP-based QUIC as the transport protocol. HTTP/3 support is optional. When enabled, HTTP/3 can fall back to HTTP/2 or HTTPS if not available.

It depends.

From the end-user-experience point of view: Yes! A user may feel that HTTP/3 is serving the site more fluently than HTTP/2. This is particularly true when the network conditions are less than optimal.

From a cost-of-service point of view: No! HTTP/3 costs more CPU cycles to push the same amount of traffic as HTTP/2. Though, this cost is likely to shrink as operating systems optimize their UDP subsystems.

HTTP/3 is based on QUIC. QUIC was originally developed by Google, and the Google version of QUIC is now referred to as gQUIC. HTTP/3 has evolved from gQUIC with contributions from the IETF working group.

HTTP/3 is the full application protocol. QUIC refers to the underlying transport protocol, which is not limited to serving HTTPS traffic.

HTTP/3 uses QUIC, which reduces the Head of Line (HoL) blocking issue. All TCP-based protocols suffer from HoL blocking, including HTTP/2.

HTTP/3, which uses QUIC as a transport layer, is a new, improved version of HTTP. Web infrastructure technology (web servers, web browsers, etc.) are being updated to support HTTP/3, and take advantage of HTTP/3's speed, reduced latency, better handling of packet errors, and built-in encryption.

To use HTTP/3 on your site, you require a web server that supports it. Alternately, you can use a content delivery network that supports HTTP/3 in front of your site.

In order for your visitors to experience a full HTTP/3 connection, they need to access your site via a browser that supports HTTP/3.

LiteSpeed has been supporting QUIC since 2017. In July of 2019, LiteSpeed was the first to introduce web server support for HTTP/3 at a production grade and capacity. The LiteSpeed implementation of QUIC and HTTP/3 is stable, production ready, and available in the following products:

•  LiteSpeed Enterprise Web Server
•  LiteSpeed ADC
•  OpenLiteSpeed

Nginx support is currently in beta

H2O, Apache Traffic Server, and hypercorn support HTTP/3 now, and more off-the-shelf server support should become available soon.