Communication Equipment

The way the SCADA system network (topology) is set up can vary with each system but there must be uninterrupted, bidirectional communication between the MTU and the RTU for a SCADA or Data Acquisition system to function properly. This can be accomplished in various ways, i.e. private wire lines, buried cable, telephone, radios, modems, microwave dishes, satellites, or other atmospheric means, and many times, systems employ more than one means of communicating to the remote site. This may include dial-up or dedicated voice grade telephone lines, DSL (Digital Subscriber Line), Integrated Service Digital Network (ISDN), cable, fiber optics, WiFi, or other broadband services.

There are many options to consider when selecting the appropriate communication equipment and can include either a public and/or private medium. Public medium is a communication service that the customer pays for on a monthly or per time or volume use. Private mediums are owned, licensed, operated and serviced by the user. If you choose to use a private medium, consider the staffing requirements necessary to support the technical and maintenance aspects of the system.

Private Media Types:

Private Wire

Sometimes it makes sense to string or bury your own cable between sites to provide continuous communication. This type of media usually is limited to low bandwidth modems.

Wireless

(Spread Spectrum Radio)

This media type is license-free and available to the public in the 900 MHz and 5.8GHz bands. The higher the frequency used in the system, the more "line of sight" it becomes. Some Spread Spectrum radio units have the ability to span distances by re-strengthening signals for the next radio in line, acting like a repeater for other units in the network. Spread Spectrum radio modems generally have built in error correction, encryption and other features that make them a reliable, secure and long-lasting solution for network communication.

(Microwave Radio)

Microwave radio transmits at high frequencies through parabolic dishes mounted on towers or on top of buildings. This media uses point-to-point, line-of-sight technology and communications may become interrupted at times due to misalignment and/or atmospheric conditions.

(VHF/UHF Radio)

Good for up to 30 miles, VHF/UHF radio is an electromagnetic transmission with frequencies of 175MHz-450MGz-900MHz received by special antennas. A license from the FCC must be obtained and coverage is limited to special geographical boundaries.

Public Media Types:

(Telephone Company)

There are different services that your local telephone company can provide including: Switched Lines, Private Leased Lines, Digital Data Service, Cellular and PCS/CDPD.

* Switched Lines: Public Switch Telephone Network (PSTN) and Generally Switched Telephone network (GSTN) are dial-up voice and data transmission networks furnished by your local telephone company.
* Private Leased Lines: Private Leased Lines (PLL) are permanently connected 24 hours a day between two or more locations and used for analog (continuously varying signal) data transmission.
* Digital Data Service: Digital Data Service (DDS) is a private leased line with a special bandwidth used to transfer data at a higher speed and lower error rate. This service is applicable for computer-to-computer links.
* Cellular: This service is equivalent to Switched Line services over landlines.
* PCS/CDPD: This service is provided by cellular companies on a monthly fee or traffic volume basis and is used when continuous communication is needed.

Other Media Types:

(WiFi-SMR)

Sometimes it makes sense to use the infrastructure of another company. WiFi equipment utilizes broadband with high data rates and is used in a "time-share" basis to communicate between sites of the system. This media type generally requires advanced protocols like TCP/IP and network type connections.

(Satellite-Geosychronous/LEO)

Geosynchronous satellite's orbits are synchronous with the earth's orbit and remain in the same position with respect to the earth. These satellites use high frequency transmissions received by parabolic dish antennas. Low Earth Orbit (LEO) satellites hand off signals to other satellites for continuous coverage and latency times are less than geosynchronous satellites due to the lower orbit.