User-space

Implementing a transport protocol in user-space helps enable quickiteration of the protocol, as it is comparatively easy to evolve theprotocol without necessitating that clients and servers update theiroperating system kernel to deploy new versions.

Nothing inherent in QUIC prevents it from being implemented and offeredby operating system kernels in the future, should someone find that agood idea.

Many implementations

One obvious effect of implementing a new transport protocol inuser-space is that we can expect to see many independent implementations.

Different applications are likely to include (or layer atop) differentHTTP/3 and QUIC implementations for the foreseeable future.