/ˈmʌltiˌkæst/
noun — "sending data to multiple specific recipients simultaneously."
Multicast is a network communication method where a single data stream is transmitted to multiple designated recipients simultaneously, rather than sending separate copies to each recipient (IP unicast) or broadcasting to all devices on a network. Multicast is widely used in applications such as live video streaming, real-time financial feeds, software updates, conferencing, and IoT sensor networks where efficiency and bandwidth conservation are critical.
Technically, multicast relies on special IP address ranges, typically 224.0.0.0 to 239.255.255.255 for IPv4, and a corresponding range in IPv6, called the multicast address space. Network routers use protocols such as Protocol Independent Multicast (PIM), Internet Group Management Protocol (IGMP), or Multicast Listener Discovery (MLD) to manage group membership and efficiently forward packets only to interested receivers. This reduces network load compared with sending multiple unicast streams.
Key characteristics of multicast include:
- Efficient bandwidth usage: a single stream serves multiple recipients.
- Group addressing: allows devices to join or leave multicast groups dynamically.
- Scalable delivery: supports large audiences without linearly increasing network load.
- Protocol support: leverages IGMP, PIM, and MLD for IP networks.
- Integration: commonly used with streaming media, conferencing tools, and IoT telemetry.
In practical workflows, multicast is used to deliver live video streams to hundreds or thousands of viewers on a corporate network without duplicating streams for each recipient. For example, a stock exchange can send real-time market data via multicast to all authorized trading terminals simultaneously, minimizing latency and conserving bandwidth. Similarly, software vendors can distribute updates via multicast to thousands of devices at once.
Conceptually, multicast is like a single water pipe branching to multiple faucets: one source supplies all destinations efficiently without needing separate pipelines for each.
Intuition anchor: Multicast acts as the network’s broadcast-efficient mechanism, delivering targeted content to multiple recipients simultaneously while conserving resources and maintaining scalability.