v144 · network / connectivity

Multicast support for Direct Sockets API

This feature allows [Isolated Web Apps](https://chromeos.dev/en/web/isolated-web-apps) (IWAs) to subscribe to multicast groups and receive User Datagram Protocol (UDP) packets from there. IWAs can now also specify additional parameters when sending UDP packets to multicast addresses.

concepts

  1. Multicast Receiver

    Direct Sockets gains multicast support — join groups, send to multicast addresses. Required for industrial / IoT discovery protocols (mDNS, SSDP, custom factory floor).

  2. IoT Discovery (mDNS)

    The motivating use case from the IWA explainer: discover printers and casters via 224.0.0.251:5353. The constructor throws outside an Isolated Web App — caught and shown.

  3. TTL & Loop Explorer

    The two knobs everyone gets wrong — dial ttl and loopback, watch a network topology fan out hop by hop and see whether the sender also receives a copy.

  4. Group Sync Demo

    Six simulated displays in a multicast group (224.0.0.251:5353). One "Broadcast packet" button sends a single UDP datagram that every joined device receives simultaneously — the shopping-mall video-wall use case. Toggle devices in/out of the group and watch the bandwidth comparison: 1 multicast packet vs N unicast packets.

why it shipped

1. Synchronous video stream from one device to the whole network of devices. For example, imagine in a shopping mall there would be multiple displays which show videos simultaneously on all devices.

references