Modbus-RTU and Modbus-TCP on an Airwall Edge Service

The Modbus protocol enables data transmission between devices using a serial interface.

Modbus-TCP applies to: 2.1.6 and higher

Beginning with v2.1.6, we have added Modbus support, making it possible to communicate over Internet or Intranet.

The following Airwall Gateways/HIPswitches support Modbus:
  • Airwall Gateway-100s (RS-232)
  • Airwall Gateway-150 (RS-232)
  • Airwall Gateway-250e/g/d (RS-232 & RS-485)
  • Airwall Gateway-300 (RS-232)

Modbus-RTU

The Modbus protocol is essentially a technique of enabling data transmission between devices using a serial interface. Our serial-enabled Airwall Gateways have been able to encapsulate Modbus-RTU (Remote Terminal Unit) over a serial line since since firmware 1.x.

With v2.1.6, we have enhanced our Serial over IP (SoIP) feature with Modbus-TCP (Transmission Control Protocol) support making it possible to communicate over Internet or Intranet.

After configuring Modbus via the Airwall Gateway SoIP settings in Conductor, the Airwall Gateway accepts Modbus-TCP commands from servers, issues the commands to serially-connected Modbus RTU devices, and returns the responses via Modbus TCP back to the server. This configuration provides optimal efficiency for Modbus traffic in terms of throughput, latency, and number of messages as compared to transparent Serial over IP.

Modbus-TCP

Modbus-TCP is a frame-aware Modbus-RTU encapsulation that is compatible with modern Modbus/SCADA systems. Unlike SoIP, Modbus-TCP processes each Modbus frame as a separate packet, and transfers the burden of error correction to the TCP protocol.