What is Multipath QUIC

Multipath QUIC extends QUIC to use multiple network paths at the same time — going beyond connection migration to actively send data over both WiFi and cellular simultaneously for better throughput and resilience.

How is it different from connection migration?

Connection migration moves a connection from one path to another — when WiFi drops, QUIC switches to cellular. It uses one path at a time.

Multipath QUIC uses both paths simultaneously. Data can be split across WiFi and cellular, or the same data can be sent on both paths for redundancy. The connection doesn't switch between paths — it uses all of them at once.

How does it work?

Multipath QUIC adds the concept of path IDs to the QUIC protocol. Each path has its own congestion control, its own round-trip time measurements, and its own packet numbering. A scheduler decides which path to use for each packet based on available bandwidth, latency, and loss rates.

Because QUIC already has connection IDs and supports stream-level independence, adding multipath is a natural extension. The receiver reassembles data from multiple paths and delivers it to the correct stream.

How is it different from Multipath TCP?

Multipath TCP extends TCP at the kernel level, which makes it vulnerable to middlebox interference — firewalls and NATs often strip MPTCP options they don't understand. Multipath QUIC runs in user space on top of UDP, making it immune to TCP middlebox issues and easier to update without OS kernel changes.

Why it matters

Multipath QUIC represents the next step in transport protocol evolution. Connection migration solved the problem of surviving network changes. Multipath solves the problem of using all available networks at once. For mobile devices that always have multiple network interfaces, this means faster downloads, more resilient connections, and better utilization of available bandwidth.