DNP3 was designed to optimize the transmission of data acquisition information and control commands from one computer to another using serial and IP communications. It is not a general-purpose protocol like those found on the Internet for transmitting email, hypertext documents, SQL queries, multimedia and huge files. It is intended for SCADA (Supervisory Control and Data Acquisition) applications.
DNP3 has been used primarily by electric and water / wastewater industry, transportation and the oil and gas industry, but it functions well for other areas. It offers flexibility and functionality that go far beyond conventional communications protocols. Among its robust and flexible features DNP3 includes:
- Output options
- Secure configuration / file transfers
- Addressing for over 65,000 devices on a single link
- Time synchronization and time-stamped events
- Broadcast messages
- Data link and application layer confirmation
- Supports any physical communication network including RS 232/485 and TCP/IP
- The DNP3 Protocol Specification is based on an Object Model
Quick understanding of DNP3 without having to comb through the tedious details of a complex specification
Protocols define the rules by which devices talk with each other, and DNP3 is a protocol for transmission of data from point A to point B using serial and IP communications.It has been used primarily by electric and water / waste water industry, transportation and the oil and gas industry, but it functions well for other areas.
A typical electric company may have a common operations center that monitors all of the equipment at each of its substations. In the operations center, a powerful computer stores all of the incoming data and displays the system for the human operators.
Substations have many devices that need monitoring (Are circuit breakers opened or closed?), current sensors (How many amperes are flowing?) and voltage transducers (What is the line potential?). That only scratches the surface; a utility is interested in monitoring many parameters, too numerous to discuss here.
The operations personnel often need to switch sections of the power grid into or out of service. Computers are situated in substations to collect the data for transmission to the master station in the operations center. The substation computers are also called upon to energize or de-energize the breakers and voltage regulators.
DNP3 uses the term outstation to denote remote computers as are found in the field. The term master is used for the computers in the control centers. DNP3 provides the rules for remotely located computers and master station computers to communicate data and control commands.
DNP3 is a non-proprietary protocol that is available to anyone by visiting the web site www.dnp.org. Only a nominal fee is charged for documentation, but otherwise it is available worldwide with no restrictions. This means a utility can purchase master station and outstation computing equipment from any manufacturer and be assured that they will reliably talk to each other. Vendors compete based upon their computing equipment’s features, costs and quality factors instead of who has the best protocol. Utilities are not bound to one manufacturer after the initial sale.
What do the computers talk about?
Outstation computers gather data for transmission to the master
• Binary input data that is useful to monitor two-state devices. For example a circuit breaker is closed or tripped; a pipeline pressure alarm shows normal or excessive.
• Analog input data that conveys voltages, currents, power, reservoir water levels and temperatures.
• Count input data that reports energy in kilowatt hours or fluid volume.
• Files that contain configuration data.
The master station issues control commands that take the form of
• Close or trip a circuit breaker, start or stop a motor, and open or close a valve.
• Analog output values to set a regulated pressure or a desired voltage level.
Other things the computers talk to each other about are synchronizing the time and date, sending historical or logged data, waveform data, and on and on.
DNP3 was designed to optimize the transmission of data acquisition information and control commands from one computer to another. It is not a general purpose protocol like those found on the Internet for transmitting email, hypertext documents, SQL
queries, multimedia and huge files. It is intended for SCADA (Supervisory Control and Data Acquisition) applications.
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