QUIC (Quick UDP Internet Connections)
QUIC (Quick UDP Internet Connections, pronounced “quick”) is a modern transport layer network protocol originally developed by Google and now standardized by the IETF. Its primary goal is to reduce latency compared to traditional TCP, especially during connection setup and in scenarios involving packet loss.
QUIC can be thought of as a combination of TCP + TLS, implemented over UDP. Unlike TCP, which is deeply embedded in operating systems and network hardware, QUIC’s design on top of UDP allows it to evolve rapidly, since it can be deployed and updated at the application level without requiring changes to kernel-level networking stacks or network infrastructure.
QUIC is already widely used in practice. Client-side implementations are built into Chromium (Chrome, Edge) and Android, and are activated when connecting to servers that support it—like Google Docs, YouTube, and other major web services. As of recent reports, around 88% of traffic from Android and Chrome desktop clients uses QUIC when communicating with Google servers.
Although there are many open-source QUIC libraries available today (see link below), commonly used file transfer tools have yet to adopt QUIC widely. That said, adoption is steadily growing as the protocol matures and HTTP/3 (which runs over QUIC) becomes the new standard for web traffic.
However, current HTTP/3 implementations typically exhibit throughput that is 2–5 times slower than HTTP/2 on high-bandwidth (e.g. 10G) links. The paper “QUIC on the Highway: Evaluating Performance on High-rate Links” offers an in-depth analysis of the underlying causes. Chief among them is the fact that QUIC operates entirely in user space, lacking the low-level optimizations and mature code paths available to kernel-space TCP stacks. This user-space execution introduces higher CPU overhead and less efficient packet processing, especially under conditions where system calls, memory copies, and context switches become bottlenecks.
Current QUIC open source library implementations:
