Taking the Best of Multicast and Unicast with Flexicast QUIC

With IP Multicast, a source can efficiently send the same information to a set of receivers attached to a multicast tree. Unfortunately, when distributing live video or large files, some receivers might be unable to join the multicast tree. Applications willing to use multicast for efficiency must also support unicast to reach all their receivers. Given the complexity of mixing unicast and multicast, most popular applications only use unicast protocols. The large deployment of QUIC, a secure and flexible transport protocol that runs above UDP, allows for reconsidering multicast at the transport layer. We design and implement Flexicast QUIC, an extension of Multipath QUIC that enables applications to use multicast where and when it works efficiently and seamlessly fall back on unicast otherwise. Our in-lab performance evaluation shows that a Flexicast QUIC source can sustain up to 1000 receivers for an aggregated traffic of more than 80 Gbps, more than 4 times what we achieve with (unicast) QUIC in the same setup. We also show that Flexicast QUIC can easily distribute a video stream and recover from transient failures on the underlying multicast tree while maintaining excellent quality of experience.