QUIC (Quick UDP Internet Connections)
Deployed for Google services since 2012
Standardized by IETF in RFC 8999, 9000 and 9001
Represents +/- 30% of broadband traffic in 2021
QUIC (Quick UDP Internet Connections, pronounced quick) is an experimental transport layer network protocol designed by Google. The overall goal is to reduce latency compared to that of TCP. Think of QUIC as being similar to TCP+TLS+HTTP/2 implemented on UDP. Because TCP is implemented at the lowest levels of machinery (operating systems, routing firmware), making changes to TCP is next to impossible given the amount of upgrades that would need to occur. Since QUIC is built on top of UDP, it suffers from no such limitations and can be integrated into end host applications.
Currently a client-side implementation exists as a part of Chromium and Android, and it is used when accessing a server side application that supports it (e.g. Google docs and drive, YouTube, etc.). Estimates are that 88% of traffic for Android and Chrome Desktop is now based on QUIC, and that interactions with Google backends can result in 5% performance improvement, and 30% less rebuffering of streaming applications. In practice the use of this protocol can offer speedups at the browser level, but the primary use case is home uses with connection speeds that are measured in the 100s of Mbps range.
More information can be found at these links: