QUIC (Quick UDP Internet Connection) is a transport layer network protocol that was initially designed by Google engineers in 2012 as an experiment to improve the performance of Googles web applications. It is an encrypted connection-oriented protocol that operates at the Transport Layer, or Layer 4, in the OSI model. QUIC is used by more than half of all connections from the Chrome web browser to Googles servers, and it is supported by Microsoft Edge and Firefox.
QUIC is built on top of UDP, which is different from HTTPS leveraging TLS, which is built on top of the TCP protocol. This comes with one clear advantage: the time to the first valuable communication drops significantly. QUIC also includes a number of other changes that improve overall latency and throughput. For instance, the packets are encrypted individually, so that they do not result in the encrypted data waiting for partial packets. This is not generally possible under TCP, where the encryption records are in a bytestream and the protocol stack is unaware of higher-layer boundaries within this stream.
QUIC relies on multiplexing, which is what gives it an edge over TCP. Where TCP uses a single end-to-end connection point, QUIC establishes multiple connections between two endpoints. If one of the streams of information is interrupted, either by shoddy connection or other outside interference, the multiple connection points will allow the streams of information to continue.
QUIC is used for apps and services that require speedy online service, such as gaming, streaming, or VoIP. It is designed to accelerate HTTP traffic as well as make it more secure, with the intended goal of eventually replacing TCP and TLS on the web.
QUIC is not without its downsides, however. It is still in its experimental stages and not widely adopted. Additionally, existing hardware and software deployed in the wild may not be able to understand it.
