The SCADA systems are built using proprietary or public communication protocols which are used for communication between an MTU and one or more RTUs. The SCADA protocols provide transmission specifications to interconnect substation computers, IEDs, RTUs, and the master station. The most common protocol used is: IEC 60870-5-101, Distributed Network Protocol version 3.0 (DNP3), and Modbus. The DNP3 and IEC protocols provide more functionality than Modbus and are used for higher data volumes. IEC protocols dominate the market in Europe whereas DNP is a major market player in North America. DNP3 protocols are also used widely in Australia and China. This report identifies SCADA protocol such as DNP3 as the right place communications in SCADA networks. Consider its greater functionality, major market role around the world, extensive use, and public distributions, it selected DNP3 to examine security enhancement approaches although most of the findings are applicable to other protocols as well.
Distributed Network Protocol (DNP3) emerged as a response to non standard utility or proprietary communication protocols, so that vendors compete based upon their computer equipment features, cost and quality factors instead of who has the best protocol. Utilities are not depending on with one manufacturer after the initial sale. The increased popularity of DNP3 is driven by industry through the DNP user group, which has since 1993 taken ownership of the protocol and assumed responsibility for its evolution. It is a public and open protocol standard that is owned and maintained by the DNP User group and DNP Technical Committee.
DNP3 is based on the early work of the IEC (International Electronical Commission) of the IEEE Standard 1379. The use of DNP3 is not limited to serial wire connections within a substation to a SCADA master using a modem and phone lines. DNP3’s contributes functionality to the protocol’s widespread use in substation local area network using TCP/IP Ethernet, fiber optic systems, on corporate frame relay network, CDPD or standard cellular systems as well as many licensed or unlicensed radio systems.