Glossary · Automation fundamentals, platforms and components
Unicast
Also known as: Point-to-point transmission
German: Unicast
In network communication, unicast is the transmission of data from one sender to exactly one receiver, identified by its unique address. It contrasts with broadcast (to all nodes in a network segment) and multicast (to a group of subscribed receivers).
- Automation components
In one sentence
Unicast sends data from one sender to exactly one addressed receiver, unlike broadcast to all nodes or multicast to a group.
Example
The HMI reads values from the PLC via unicast, while the drives receive synchronization frames via multicast.
How it applies
- Engineering: Most client-server communication, such as OPC UA client-server, Modbus TCP or web access, is unicast. Publish-subscribe and some real-time protocols use multicast to reach many devices efficiently.
- Network design: Heavy broadcast or multicast traffic can overload devices; switch features such as IGMP snooping and VLANs limit it. Unicast traffic is easier to filter with firewalls.
- Documentation: Network and interface documentation should state whether a device uses unicast, multicast or broadcast, with the addresses and ports, so that network administrators can configure switches and firewalls correctly.
Unicast vs. multicast
Unicast sends a separate copy to each receiver. Multicast sends one stream that the network delivers to all subscribed receivers, which saves bandwidth but needs network support.