The Modbus protocol defines the message structure and
communication rules used by process control systems
to exchange supervisory control and data acquisition
(SCADA) information for operating and controlling industrial
processes [1]. Modbus’ open protocol specifications and TCP
extension have contributed to its popularity, especially in
the oil and gas sector, where it is the predominant control
protocol for pipeline operations.
The Modbus protocol has two principal variants, Modbus
Serial [6] and Modbus TCP [5]. In the Modbus Serial
protocol, messages are transmitted between a master and
slaves (field devices) over serial lines using the ASCII or
RTU transmission modes. The newer Modbus TCP protocol
provides connectivity within a Modbus network (master
and its slaves) as well as for IP-interconnected Modbus
networks (multiple masters, each communicating with
possibly overlapping sets of slaves). The TCP variant enables
a master to have multiple outstanding transactions and
permits a slave to eng