스카다

스카다 또는 감시 제어 및 데이터 취득(영어: Supervisory Control And Data Acquisition)은 일반적으로 산업 제어 시스템(영어: Industrial Control Systems, ICS), 즉 다음과 같은 산업 공정/기반 시설/설비를 바탕으로 한 작업공정을 감시하고 제어하는 컴퓨터 시스템을 말한다.

• 산업 공정은 제조, 생산, 발전, 가공, 제련과정 등에 필요한 작업 절차를 의미하며, 연속/집단/반복/분산 방식으로 운용될 수 있다.
• 기반 시설 공정은 공공기관이나 사기업에 의해 이루어지는 물 처리 와 분배, 폐수 수거/처리, 기름/가스 파이프라인, 송전 및 배전, 풍력발전소, 방공 및 민방위 시스템, 대규모 통신 시스템 등에 필요한 공정을 의미한다.
• 설비 공정은 역시 공공기관이나 사기업에 의해 이루어지는 건축, 공항, 조선, 우주정거장 사업 등에 사용되는 작업공정을 의미한다. 여기서는 공조 설비, 진입로, 에너지 소모 등을 감시하고 제어한다.

구성 요소

스카다 시스템은 일반적으로 다음과 같은 구성 요소를 갖는다.

• 인간-기계 인터페이스(영어: Human-Machine Interface, HMI): 기계 제어에 사용되는 데이터를 인간에게 친숙한 형태로 변환하여 보여주는 장치로, 이것을 통해 관리자가 해당 공정을 감시하고 제어하게 된다.
• 감시 (컴퓨터) 시스템: 프로세스와 관련된 자료를 수집하고, 하드웨어 제어를 위한 실질적인 명령을 내린다.
• 원격 단말기(영어: Remote Terminal Unit, RTU): 공정에 설치된 센서와 직접 연결되며, 여기서 나오는 신호를 컴퓨터가 인식할 수 있는 디지털 데이터로 상호 변환하고, 그 데이터를 감시 시스템에 전달한다.
• 프로그래머블 로직 컨트롤러: 실제 현장에 배치되는 기기로서, 특정 용도를 위해 설계된 원격 단말기(RTU)보다 경제적이고 다목적으로 사용이 가능하다.
• 통신 시설: 제어 시스템, 원격 단말기 등 멀리 떨어져 있는 요소들이 서로 통신할 수 있도록 해준다.
• 다양한 공정과 분석적인 기기 장치

감시와 제어의 차이

스카다 시스템과 분산 제어 시스템(영어: Distributed Control System, DCS)을 혼동하는 경우가 있다. 일반적으로, 스카다 시스템은 작업 공정을 조직화하는 쪽이며, 실시간으로 공정을 제어하지는 않는다. 하지만, 통신 기술의 발달로 인해 거리상의 제약이 적고 안정적이며 레이턴시가 적고 속도도 빠른 통신이 가능해짐에 따라 실시간 제어에 관한 논의는 다소 모호한 상태가 되었다. 즉, 스카다와 DCS의 차이점으로 언급되던 것들도 대부분 시스템 분류에 따른 의미상의 차이만 남게 되었으며, 실질적인 차이는 무시할 수 있을 정도이다. 통신 기술의 발달 덕분에, 두 시스템간의 차이는 사실상 사라지게 될 것이다.

정리하자면,

• DCS는 공정 기반이지만, SCADA는 데이터 취합 기반이다.
• DCS는 공정 주도 방식으로 동작하지만, SCADA는 사건(이벤트) 주도 방식으로 동작한다.
• DCS는 하나의 현장에서 이루어지는 작업들을 처리하는 데에 주로 사용되고, 스카다는 지리적으로 널게 분산되는 형태의 응용분야에서 선호된다.

Systems concepts

The term SCADA usually refers to centralized systems which monitor and control entire sites, or complexes of systems spread out over large areas (anything from an industrial plant to a nation). Most control actions are performed automatically by RTUs or by PLCs. Host control functions are usually restricted to basic overriding or supervisory level intervention. For example, a PLC may control the flow of cooling water through part of an industrial process, but the SCADA system may allow operators to change the set points for the flow, and enable alarm conditions, such as loss of flow and high temperature, to be displayed and recorded. The feedback control loop passes through the RTU or PLC, while the SCADA system monitors the overall performance of the loop.

Data acquisition begins at the RTU or PLC level and includes meter readings and equipment status reports that are communicated to SCADA as required. Data is then compiled and formatted in such a way that a control room operator using the HMI can make supervisory decisions to adjust or override normal RTU (PLC) controls. Data may also be fed to a Historian, often built on a commodity Database Management System, to allow trending and other analytical auditing.

SCADA systems typically implement a distributed database, commonly referred to as a tag database, which contains data elements called tags or points. A point represents a single input or output value monitored or controlled by the system. Points can be either "hard" or "soft". A hard point represents an actual input or output within the system, while a soft point results from logic and math operations applied to other points. (Most implementations conceptually remove the distinction by making every property a "soft" point expression, which may, in the simplest case, equal a single hard point.) Points are normally stored as value-timestamp pairs: a value, and the timestamp when it was recorded or calculated. A series of value-timestamp pairs gives the history of that point. It's also common to store additional metadata with tags, such as the path to a field device or PLC register, design time comments, and alarm information.

Human–machine interface

파일:Scada std anim.gif

Typical basic SCADA animations

A human–machine interface or HMI is the apparatus which presents process data to a human operator, and through which the human operator controls the process.

An HMI is usually linked to the SCADA system's databases and software programs, to provide trending, diagnostic data, and management information such as scheduled maintenance procedures, logistic information, detailed schematics for a particular sensor or machine, and expert-system troubleshooting guides.

The HMI system usually presents the information to the operating personnel graphically, in the form of a mimic diagram. This means that the operator can see a schematic representation of the plant being controlled. For example, a picture of a pump connected to a pipe can show the operator that the pump is running and how much fluid it is pumping through the pipe at the moment. The operator can then switch the pump off. The HMI software will show the flow rate of the fluid in the pipe decrease in real time. Mimic diagrams may consist of line graphics and schematic symbols to represent process elements, or may consist of digital photographs of the process equipment overlain with animated symbols.

The HMI package for the SCADA system typically includes a drawing program that the operators or system maintenance personnel use to change the way these points are represented in the interface. These representations can be as simple as an on-screen traffic light, which represents the state of an actual traffic light in the field, or as complex as a multi-projector display representing the position of all of the elevators in a skyscraper or all of the trains on a railway.

An important part of most SCADA implementations is alarm handling. The system monitors whether certain alarm conditions are satisfied, to determine when an alarm event has occurred. Once an alarm event has been detected, one or more actions are taken (such as the activation of one or more alarm indicators, and perhaps the generation of email or text messages so that management or remote SCADA operators are informed). In many cases, a SCADA operator may have to acknowledge the alarm event; this may deactivate some alarm indicators, whereas other indicators remain active until the alarm conditions are cleared. Alarm conditions can be explicit—for example, an alarm point is a digital status point that has either the value NORMAL or ALARM that is calculated by a formula based on the values in other analogue and digital points—or implicit: the SCADA system might automatically monitor whether the value in an analogue point lies outside high and low limit values associated with that point. Examples of alarm indicators include a siren, a pop-up box on a screen, or a coloured or flashing area on a screen (that might act in a similar way to the "fuel tank empty" light in a car); in each case, the role of the alarm indicator is to draw the operator's attention to the part of the system 'in alarm' so that appropriate action can be taken. In designing SCADA systems, care is needed in coping with a cascade of alarm events occurring in a short time, otherwise the underlying cause (which might not be the earliest event detected) may get lost in the noise. Unfortunately, when used as a noun, the word 'alarm' is used rather loosely in the industry; thus, depending on context it might mean an alarm point, an alarm indicator, or an alarm event.

Hardware solutions

SCADA solutions often have distributed control system (DCS) components. Use of "smart" RTUs or PLCs, which are capable of autonomously executing simple logic processes without involving the master computer, is increasing. A standardized control programming language, IEC 61131-3 (a suite of 5 programming languages including Function Block, Ladder, Structured Text, Sequence Function Charts and Instruction List), is frequently used to create programs which run on these RTUs and PLCs. Unlike a procedural language such as the C programming language or FORTRAN, IEC 61131-3 has minimal training requirements by virtue of resembling historic physical control arrays. This allows SCADA system engineers to perform both the design and implementation of a program to be executed on an RTU or PLC. A programmable automation controller (PAC) is a compact controller that combines the features and capabilities of a PC-based control system with that of a typical PLC. PACs are deployed in SCADA systems to provide RTU and PLC functions. In many electrical substation SCADA applications, "distributed RTUs" use information processors or station computers to communicate with digital protective relays, PACs, and other devices for I/O, and communicate with the SCADA master in lieu of a traditional RTU.

Since about 1998, virtually all major PLC manufacturers have offered integrated HMI/SCADA systems, many of them using open and non-proprietary communications protocols. Numerous specialized third-party HMI/SCADA packages, offering built-in compatibility with most major PLCs, have also entered the market, allowing mechanical engineers, electrical engineers and technicians to configure HMIs themselves, without the need for a custom-made program written by a software developer.

Remote terminal unit

The RTU connects to physical equipment. Typically, an RTU converts the electrical signals from the equipment to digital values such as the open/closed status from a switch or a valve, or measurements such as pressure, flow, voltage or current. By converting and sending these electrical signals out to equipment the RTU can control equipment, such as opening or closing a switch or a valve, or setting the speed of a pump. It can also control the flow of a liquid.

Supervisory station

The term supervisory station refers to the servers and software responsible for communicating with the field equipment (RTUs, PLCs, etc.), and then to the HMI software running on workstations in the control room, or elsewhere. In smaller SCADA systems, the master station may be composed of a single PC. In larger SCADA systems, the master station may include multiple servers, distributed software applications, and disaster recovery sites. To increase the integrity of the system the multiple servers will often be configured in a dual-redundant or hot-standby formation providing continuous control and monitoring in the event of a server failure.

Operational philosophy

For some installations, the costs that would result from the control system failing are extremely high. Possibly even lives could be lost. Hardware for some SCADA systems is ruggedized to withstand temperature, vibration, and voltage extremes. In the most critical installations, reliability is enhanced by having redundant hardware and communications channels, up to the point of having multiple fully equipped control centres. A failing part can be quickly identified and its functionality automatically taken over by backup hardware. A failed part can often be replaced without interrupting the process. The reliability of such systems can be calculated statistically and is stated as the mean time to failure, which is a variant of mean time between failures. The calculated mean time to failure of such high reliability systems can be on the order of centuries.

Communication infrastructure and methods

SCADA systems have traditionally used combinations of radio and direct wired connections, although SONET / SDH is also frequently used for large systems such as railways and power stations. The remote management or monitoring function of a SCADA system is often referred to as telemetry. Some users want SCADA data to travel over their pre-established corporate networks or to share the network with other applications. The legacy of the early low-bandwidth protocols remains, though.

SCADA protocols are designed to be very compact. Many are designed to send information only when the master station polls the RTU. Typical legacy SCADA protocols include Modbus RTU, RP-570, Profibus and Conitel. These communication protocols are all SCADA-vendor specific but are widely adopted and used. Standard protocols are IEC 60870-5-101 or 104, IEC 61850 and DNP3. These communication protocols are standardized and recognized by all major SCADA vendors. Many of these protocols now contain extensions to operate over TCP/IP.

Although some believe it is good security engineering practice to avoid connecting SCADA systems to the Internet so the attack surface is reduced, many industries, such as wastewater collection and water distribution, have used existing cellular networks to monitor their infrastructure along with internet portals for end-user data delivery and modification. Cellular network data is encrypted before transmission over the Internet.

With increasing security demands ( such as North American Electric Reliability Corporation (NERC) and critical infrastructure protection (CIP) in the US), there is increasing use of satellite-based communication. This has the key advantages that the infrastructure can be self contained (not using circuits from the public telephone system), can have built-in encryption, and can be engineered to the availability and reliability required by the SCADA system operator. Earlier experiences using consumer-grade VSAT were poor. Modern carrier-class systems provide the quality of service required for SCADA.

RTUs and other automatic controller devices were developed before the advent of industry wide standards for interoperability. The result is that developers and their management created a multitude of control protocols. Among the larger vendors, there was also the incentive to create their own protocol to "lock in" their customer base. A list of automation protocols is being compiled here.

Recently, OLE for process control (OPC) has become a widely accepted solution for intercommunicating different hardware and software, allowing communication even between devices originally not intended to be part of an industrial network.

SCADA architectures

The United States Army's Training Manual 5-601 covers "SCADA Systems for C4ISR Facilities".

SCADA systems have evolved through 3 generations as follows:

First generation: "Monolithic"

In the first generation, computing was done by mainframe computers. Networks did not exist at the time SCADA was developed. Thus SCADA systems were independent systems with no connectivity to other systems. Wide Area Networks were later designed by RTU vendors to communicate with the RTU. The communication protocols used were often proprietary at that time. The first-generation SCADA system was redundant since a back-up mainframe system was connected at the bus level and was used in the event of failure of the primary mainframe system.

Second generation: "Distributed"

The processing was distributed across multiple stations which were connected through a LAN and they shared information in real time. Each station was responsible for a particular task thus making the size and cost of each station less than the one used in First Generation. The network protocols used were still mostly proprietary, which led to significant security problems for any SCADA system that received attention from a hacker. Since the protocols were proprietary, very few people beyond the developers and hackers knew enough to determine how secure a SCADA installation was. Since both parties had vested interests in keeping security issues quiet, the security of a SCADA installation was often badly overestimated, if it was considered at all.

Third generation: "Networked"

Due to the usage of standard protocols and the fact that many networked SCADA systems are accessible from the Internet, the systems are potentially vulnerable to remote cyber-attacks. On the other hand, the usage of standard protocols and security techniques means that standard security improvements are applicable to the SCADA systems, assuming they receive timely maintenance and updates.

Security issues

The move from proprietary technologies to more standardized and open solutions together with the increased number of connections between SCADA systems and office networks and the Internet has made them more vulnerable to attacks—see references. Consequently, the security of some SCADA-based systems has come into question as they are seen as potentially vulnerable to cyber attacks.

In particular, security researchers are concerned about:

• the lack of concern about security and authentication in the design, deployment and operation of some existing SCADA networks
• the belief that SCADA systems have the benefit of security through obscurity through the use of specialized protocols and proprietary interfaces
• the belief that SCADA networks are secure because they are physically secured
• the belief that SCADA networks are secure because they are disconnected from the Internet.

SCADA systems are used to control and monitor physical processes, examples of which are transmission of electricity, transportation of gas and oil in pipelines, water distribution, traffic lights, and other systems used as the basis of modern society. The security of these SCADA systems is important because compromise or destruction of these systems would impact multiple areas of society far removed from the original compromise. For example, a blackout caused by a compromised electrical SCADA system would cause financial losses to all the customers that received electricity from that source. How security will affect legacy SCADA and new deployments remains to be seen.

There are two distinct threats to a modern SCADA system. First is the threat of unauthorized access to the control software, whether it be human access or changes induced intentionally or accidentally by virus infections and other software threats residing on the control host machine. Second is the threat of packet access to the network segments hosting SCADA devices. In many cases, there is rudimentary or no security on the actual packet control protocol, so anyone who can send packets to the SCADA device can control it. In many cases SCADA users assume that a VPN is sufficient protection and are unaware that physical access to SCADA-related network jacks and switches provides the ability to totally bypass all security on the control software and fully control those SCADA networks. These kinds of physical access attacks bypass firewall and VPN security and are best addressed by endpoint-to-endpoint authentication and authorization such as are commonly provided in the non-SCADA world by in-device SSL or other cryptographic techniques.

The reliable function of SCADA systems in our modern infrastructure may be crucial to public health and safety. As such, attacks on these systems may directly or indirectly threaten public health and safety. Such an attack has already occurred, carried out on Maroochy Shire Council's sewage control system in Queensland, Australia. Shortly after a contractor installed a SCADA system there in January 2000 system components began to function erratically. Pumps did not run when needed and alarms were not reported. More critically, sewage flooded a nearby park and contaminated an open surface-water drainage ditch and flowed 500 meters to a tidal canal. The SCADA system was directing sewage valves to open when the design protocol should have kept them closed. Initially this was believed to be a system bug. Monitoring of the system logs revealed the malfunctions were the result of cyber attacks. Investigators reported 46 separate instances of malicious outside interference before the culprit was identified. The attacks were made by a disgruntled employee of the company that had installed the SCADA system. The employee was hoping to be hired full time to help solve the problem.

Many vendors of SCADA and control products have begun to address the risks posed by unauthorized access by developing lines of specialized industrial firewall and VPN solutions for TCP/IP-based SCADA networks as well as external SCADA monitoring and recording equipment. Additionally, application whitelisting solutions are being implemented because of their ability to prevent malware and unauthorized application changes without the performance impacts of traditional antivirus scans. Also, the ISA Security Compliance Institute (ISCI) is emerging to formalize SCADA security testing starting as soon as 2009. ISCI is conceptually similar to private testing and certification that has been performed by vendors since 2007. Eventually, standards being defined by ISA99 WG4 will supersede the initial industry consortia efforts, but probably not before 2011.

The increased interest in SCADA vulnerabilities has resulted in vulnerability researchers discovering vulnerabilities in commercial SCADA software and more general offensive SCADA techniques presented to the general security community. In electric and gas utility SCADA systems, the vulnerability of the large installed base of wired and wireless serial communications links is addressed in some cases by applying bump-in-the-wire devices that employ authentication and Advanced Encryption Standard encryption rather than replacing all existing nodes.

In June 2010, VirusBlokAda reported the first detection of malware that attacks SCADA systems (Siemens' WinCC/PCS7 systems) running on Windows operating systems. The malware is called Stuxnet and uses four zero-day attacks to install a rootkit which in turn logs in to the SCADA's database and steals design and control files. The malware is also capable of changing the control system and hiding those changes. The malware was found by an anti-virus security company on 14 systems, the majority of which were located in Iran.

See also

• BACnet
• LonWorks
• Modbus
• Telemetry

External links

• UK SCADA security guidelines
• BBC NEWS | Technology | Spies 'infiltrate US power grid'