Modbus TCP - Can any IEDs on the ethernet initiate a command to its peer?


Thread Starter


In a substation with IEDs for protection working on TCP/Modbus, can any IED be a MASTER and initiate a command to its peer? If yes, any limit on number of masters at any given time? Hope ONLY ONE MASTER at a time. Please clarify.
Modbus TCP by itself is not peer to peer, but it is possible for an IED to have Modbus TCP Client (Master) and Server (Slave) supported at the same time. In this case it is possible to send out a command to the other IED. Modbus TCP does not limit number of Client/Master that can be connected to a Server/Slave, but normally IEDs limit this count by a configuration setting. Modbus TCP may be not be a good option to use exchanging critical and priority information. You can consider IEC-61850 Goose messages in case you have not yet decided on the protocol supported, IED make and manufacturer.

Jose Thomas

Schneider Italy

Modbus TCP protocol is a multi-master protocol, and there's no limitation on the number of masters.