MsQuic is a Microsoft implementation of the IETF QUIC protocol. It is cross platform, written in C and designed to be a general purpose QUIC library.

Important The MsQuic library, as well as the protocol itself, is still a work in progress. Version 1 is not yet finalized and may continue to experience breaking changes until it is finalized.

QUIC has many benefits when compared to existing TLS over TCP scenarios:

• Handshake authenticated with TLS 1.3
• All packets are encrypted
• Parallel streams of application data.
• Improved (compared to TCP) congestion control and loss recovery.
• Exchange application data in the first round trip (0-RTT).
• Survives a change in the clients IP address or port.
• Easily extendable for new features (such as unreliable delivery).

Important Several QUIC protocol features are not yet fully implemented:

• 0-RTT
• Client-side Migration
• Server Preferred Address
• Path MTU Discovery

• Cross-platform support.
• Optimized for client and server.
• Optimized for maximal throughput and minimal latency.
• Asynchronous IO.
• Receive side scaling (RSS).
• UDP send and receive coalescing support.

MsQuic currently officially supports the following platform configurations. Information on support for MsQuic itself is located here.

On Windows 10, MsQuic relies on built-in support from Schannel for TLS 1.3 functionality. MsQuic is shipped in-box in the Windows kernel in the form of the msquic.sys driver, to support built-in HTTP and SMB features. User mode applications use msquic.dll (built from here) and package it with their app.

Important This configuration requires running the latest Windows Insider Preview Builds for Schannel's TLS 1.3 support.

Important This configuration does not support 0-RTT due to Schannel's current lack of support.

On Linux, MsQuic relies on OpenSSL for TLS 1.3 functionality.

Important This configuration relies on an outstanding pull request to OpenSSL master for QUIC/TLS support. It is still currently unknown as to when it will be merged into master. See here for more details.

Important This configuration does not support 0-RTT. Complete integration with OpenSSL is an ongoing effort.

For testing or experimentation purposes, MsQuic may be built with other configurations, but they are not to be considered officially supported unless they are listed above. Any bugs found while using these configurations may be looked at, but no guarantees are provided that they will be fixed.

• For building the library, see the Build docs.
• For using the library, see the API docs or the Sample.
• For other frequently asked questions, see the FAQs.

For information on contributing, please see our contribution guidlines.

Important - We are still bringing up important regression tests for the core code. Until they are onboarded, any external contributions to the core or kernel mode files in the platform will not be accepted. This is only a temporary restriction and we are working to complete it by the end of 2020.