COMMUNICATION NETWORK General Overview of SCADA Communications

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Cellular Based on the cellular phone technology to transmit data regardless of distance but. dependent on cellular signal coverage, Satellite Similar to the cellular phone platform but utilizing satellites instead of ground based. cellular towers, Wi Fi A technology increasing in popularity that allows an electronic device to exchange data. wirelessly using radio waves over a computer network including high speed internet. connections Earlier generation Wi Fi systems can be notoriously insecure Wireless Equivalent. Privacy WEP is relatively easy to compromise so care must be taken when selecting Wi Fi. equipment to ensure that it supports robust security WPA2 is present in almost all currently. available equipment and its use should be mandated. Microwave A system for providing long range connectivity between two sites utilizing either. inexpensive public frequencies or FCC licensed spectrum Some microwave units are an. extension of Wi Fi but for long range 20 miles others use proprietary protocols. To meet security and performance specifications it is important to consider the endpoint of each. connection Point to point connections such as Ethernet Fiber and Microwave typically. terminate at a central system management facility Cellular systems may provide an Internet. connection requiring additional security and phone line systems must be protected against. security breaches through the standard land line twisted pair copper wire network. It is also important to consider the privacy offered by a solution wireless solutions in particular. need to pay attention to the possibility of a nearby device eavesdropping on an otherwise secure. conversation This can have profound implications if private data such as passwords are included. in the gathered data, Finally it is important to remember that these technologies are not mutually exclusive A site can. readily use a combination of Wi Fi and Ethernet locally and transmit the entirety of the site s. data to a central point through fiber microwave or other longer range technology. All of these communications methods fall under either hardwire or wireless category Hardwire. communication options include dedicated hardwire i e Ethernet cable fiber optic i e light. pipe telephone wire i e copper pair or coaxial cable Options for wireless data transmission. include but are not limited to include satellite radio cellular and Wi Fi Current industry trends. suggest that wireless communication systems will continue to gain a larger market sector of the. SCADA communication platforms especially for large distributed networks such as water. distribution systems where there is a need for a vast coverage area perhaps in remote locations. not readily accessible to existing hardwires The same industry trends indicate that Ethernet is. becoming the preferred communications standard for local area SCADAs such as a water. treatment plant Ritchie 2011, Wireless and hardwire options can be used alone or in tandem depending on the size and nature. of the system Factors to consider in selecting communication options include. Coverage area of SCADA system For example is the SCADA only for the local water plant or. does it include an entire widely dispersed distribution system as well as the water plant. If a system wide SCADA then consideration must be given to the size and terrain of the. distribution system For example wireless may be a less expensive option but the. communications system would require adequate line of sight between the radio. transmitters receivers, Local availability of infrastructure and its proximity to the system feature that will require a.
SCADA sensor is also relevant For example if an there is an existing telephone line to a. particular site where a sensor needs to be installed then that telephone line may be the best. Growth of the community could affect the SCADA system performance and future expandability. as well as the ability to upgrade the system easily and budget for the system. Some of the more significant advantages and disadvantages are summarized in Table 1 Most. modern SCADA systems use a variety of communication options within one system to meet their. needs Typically there is not a one size fits all solution and SCADA communications should be. tailor made to fit a utility s needs, Communications Network Features and Considerations. When selecting a communications system for plant operations it is common to use only. hardwire to connect remote equipment to the SCADA Master given the short distances involved. When using hardwired lines to communicate with remote sites in the distribution system. distance reliability and time responses are all limiting factors in the design process New. construction of hardwire communication networks are not practical when trying to connect to. distant system components such as a pump station on the other side town In situations where it. is not economically feasible to run an independent hardwire for each remote site one may elect. to tap into existing infrastructure or elect to use a form of wireless communication If a utility. elects to use pre existing infrastructure several options are available including dial up or leased. telephone lines or fiber networks The type of platform selected often depends on the bandwidth. required to perform remote operations such as pumping or the polling frequency e g how often. do you need to collect data, Inaccessible sites or lack of wire type of infrastructure may necessitate the use of wireless. communications systems but regardless of terrain distance or accessibility current trends. suggest a growing affinity to use wireless options to replace hardwire systems Wireless. communication provides utilities with the following benefits versus traditional hardwire systems. scalability deployment speed reduced network and construction costs and reduced maintenance. and repair of hard wires The scalability or ability to quickly expand as the system grows of a. wireless network is a great advantage over wired systems Increasing SCADA system coverage. can be achieved without running wire or other costly labor items and can be installed in a. relatively short period of time which offers savings over hardwire systems Wireless systems. can also expand independent of existing infrastructure to meet the needs of a growing. community The advantages of wireless can be seen in Figure 2 2 3 A Consider the image in. this figure spread out over a twenty square mile area and the relative costs of a wireless system. versus a hardwire system Now consider the replacement costs after 20 years of technological. innovation The ability to upgrade remote sites on an individual basis versus system wide is a. clear advantage and provides a degree of assurance as land lines become phased out Existing. hardwire systems may also be supplemented with wireless systems on a per unit level as new. operations come on line For cellular systems reliability and availability of service should be. taken in to consideration,Advantages Disadvantages. Telephone Line May already exist to site s Very May be monthly lease charge s Consider who. mature technology is responsible for fixing problems on the line and. if it is a third party what is their track record for. repair responses Typically slow and limited,data transmission. Ethernet Good application for local site such as Limited application range Cannot be utilized. a water treatment plant over distances greater than 1000 without. boosting signal Can be prone to lightning,damage without significant protection measures.
Fiber Optic Best direct connection with the fastest May be significant monthly lease charge s If. data transmission Large bandwidth the fiber does not already exist the capital costs. allows for video applications i e for the initial project could have a very high. security cameras to part of the SCADA Fiber is also typically very expensive to repair. Coaxial Cable May already exist to the site s Very May be monthly lease charge s Depending on. mature technology Better data the setting this type of hardwire is less common. bandwidth than a telephone line than a telephone line. Advantages Disadvantages, UHF and VHF Generally very low maintenance and FCC license required along with periodic fees. Voice Radio can usually be repaired by a local radio and renewals. 900Mhz spread No FCC license necessary and transmit Requires line of sight for best application Some. spectrum and data at a higher rate 900Mhz require FCC license. 2 4Ghz Data Radio, Wi Fi Potentially very good option for a local Very limited ranges typically 300 ft or less and. site application such as a water the signal can be significantly diminished by. treatment plant structures Wi Fi requires careful security. assessment, Microwave Potentially very good option for linking Requires expert assistance with installation. sites with good elevation such as water Some frequencies require FCC licensing. Cellular Quickly gaining in popularity The area for coverage should have good. especially as pricing continues to consistent cellular coverage. decline and for areas that may not have,strong radio signals or line of sight. conditions, Satellite Good application where there is no or May become a viable option in the future but is.
unreliable cell coverage such as currently not cost effective except in the most. extreme terrains very remote locations extreme cases. Table 1 Differences between hard wired and wireless communication systems. Figure 2 Typical SCADA Communication Network Configuration. Communication Security, Security is an important consideration when designing a SCADA network Many existing. SCADA systems have been found wanting in this regard leaving essential systems vulnerable to. outside influence,Security should be considered on three levels. Perimeter Security limiting access to systems and network equipment from. unauthorized sources, Interior Security requiring at the very least a login to access important infrastructure. Transport Security ensuring that it is difficult to illicitly access a network segment in. an attempt to gain control, Additionally a cohesive security plan requires the following components. Authentication answering the question who are you This is typically handled with a. login requirement user s name and password although more secure systems are. possible Ideally a system should be compatible with a centralized login security system. preventing the need to visit each device in order to revoke authorization whenever. personnel changes, Authorization answering the question what are you allowed to do This dove tails.
with authentication Again an ideal system will centralize this authority permitting rapid. revocation of authorization in the event of personnel changes or a security breach. Accounting answering the question who did what In essence this is an audit trail. allowing you to see which user performed what operation and when they did it This can. be an essential element of understanding an incident after it occurs or catching it as it. COMMUNICATION NETWORK General Overview of SCADA Communications Without a properly designed communication network system a SCADA system cannot exist All supervisory control and data acquisition aspects of the SCADA system rely entirely on the communication system to provide a conduit for flow of data between the supervisory controls the data acquisition units and any controllers that may be

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