Supervisory Control and Data Acquisition (SCADA)

IoT is a relatively new technology in networking technologies and protocols, with IP being the de facto standard for computer networking. Older protocols, such as Supervisory Control and Data Acquisition (SCADA), have evolved to utilize IP, allowing for real-time, data-driven decisions to improve business processes. SCADA networks are mainly concentrated in utilities and manufacturing/industrial verticals, using protocols like Modbus, DNP3, IEC 60870-5-101, DLMS/COSEM, and ANSI C12 for advanced meter reading. 

 

These protocols, which date back decades and are serial-based, require certain accommodations from both protocol and implementation perspectives when transporting them over current IoT and traditional networks. Various SCADA transport methods will be discussed in upcoming sections, focusing on these accommodations and other adjustments. SCADA networks can be found across various industries, but are mainly used in utilities and manufacturing/industrial verticals.

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Adapting SCADA for IP

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In the 1990s, the adoption of Ethernet networks in the industrial world led to the evolution of SCADA application layer protocols. The IEC adopted the Open System Interconnection (OSI) layer model and other protocol user groups modified their protocols to run over an IP infrastructure. This move allowed for the integration of existing equipment and standards while integrating SCADA subnetworks with corporate WAN infrastructures. 

 

Protocol specifications were updated to support legacy industrial protocols over IP networks, assigning TCP/UDP port numbers to protocols like DNP3, Modbus messaging service, IEC 60870-5-104, and DLMS User Association. These legacy serial protocols have evolved to utilize IP and TCP/UDP as networking and transport mechanisms, allowing utilities and companies to continue leveraging their investment in equipment and infrastructure.

DNP3 is a representative use case of these legacy serial protocols, which is based on a master/slave relationship. The IEEE 1815-2012 specification defines connection management between the DNP3 protocol and the IP layers, ensuring that each piece of the protocol stack in one station logically communicates with the respective part in the other. Master stations can parse multiple DNP3 data link layer frames from a single UDP datagram, while DNP3 data link layer frames cannot span multiple UDP datagrams. Single or multiple connections to the master may be established while a TCP keepalive timer monitors the status of the connection.

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Tunneling Legacy SCADA over IP Networks

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The deployment of legacy industrial protocols, such as DNP3 and SCADA protocols, in modern IP networks requires flexibility to integrate multiple generations of devices or operations tied to different releases and versions of application servers. Native support for IP can vary and may require different solutions. Ideally, end-to-end native IP support is preferred, using a solution like IEEE 1815-2012 for DNP3. Otherwise, transport of the original serial protocol over IP can be achieved either by tunneling using raw sockets over TCP or UDP or by installing an intermediate device that performs protocol translation between the serial protocol version and its IP implementation.

A raw socket connection refers to the serial data being packaged directly into a TCP or UDP transport. Modern industrial application servers may support this capability, while older versions typically require another device or piece of software to handle the transition from pure serial data to serial over IP using a raw socket. In Figure 6-3, routers connect via serial interfaces to remote terminal units (RTUs), which are often associated with SCADA networks.

In Scenario A, both the SCADA server and RTUs have a direct serial connection to their respective routers. The routers terminate the serial connections at both ends of the link and use raw socket encapsulation to transport the serial payload over the IP network. 

 

In Scenario B, a piece of software is installed on the SCADA server that maps the serial COM ports to IP ports, known as an IP/serial redirector. 

 

In Scenario C, the SCADA server supports native raw socket capability, allowing full IP support for raw socket connections.

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SCADA Protocol Translation

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Protocol translation is a method used to transport legacy serial data across an IP network, converting the legacy serial protocol to a corresponding IP version. This is illustrated in Figure 6-4, where two serially connected DNP3 RTUs and two master applications control and pull data from the RTUs. The IoT gateway performs a protocol translation function, enabling communication between the RTUs and servers despite the serial connection on one side and an IP connection on the other. This allows the gateway to implement a computing function close to the network edge, thereby scaling distributed intelligence in IoT networks. This can be done on IoT gateways or routers, or directly on a node connecting multiple sensors, known as fog computing.

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Happy Exploring!