Sometimes, if you're not used to dealing with industrial communications, you may not exactly know what some terms mean, like master or client. A master is a device that is actively polling for data from one or multiple devices using a serial communication protocol. A slave is the counterpart of the master. It is a passive device, waiting for the master to poll for data to actually send it. Some examples of devices or protocols using master/slave communication are Modbus® RTUs, IEC 60870-5-101, DNP 3.0, PROFIBUS, and HART.
A client is a device that is actively polling for data from one or multiple devices. A server device is the passive component, waiting for the client to poll for data to actually send it.Modbus TCP/IP, 60870-5-104, IEC 61850, and PROFINET are some protocols using client/server communication.
Basically, the master/client gives orders, the slave/server acts – just like in a restaurant!
To learn more about Industrial communications watch these videos:http://psft.com/B20