QUIC (Quick UDP Internet Connections) 是 Google 發明的協定,主要是希望改善 TCP + TLS 的反應速度,目前是用來加速 Google Chrome 與 Google server 之間的連線。
與 SPDY 或 HTTP/2 不同的地方在於使用了 UDP,這降低了 TCP packet loss 造成的壅塞現象,以及 TCP 3-way handshake 的成本,而這兩點在行動平台上都特別明顯。

依照最新的說法,目前 Google Chrome 連到 Google server 大約有一半的連線會走 QUIC:「A QUIC update on Google’s experimental transport」。
Today, roughly half of all requests from Chrome to Google servers are served over QUIC and we’re continuing to ramp up QUIC traffic, eventually making it the default transport from Google clients — both Chrome and mobile apps — to Google servers.
而在 YouTube 的改善也很大:
These benefits are even more apparent for video services like YouTube. Users report 30% fewer rebuffers when watching videos over QUIC. This means less time spent staring at the spinner and more time watching videos.
由於效果不錯,他們打算要換更多...