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Application Of Wireless Access TO SCADA System


									Application of wireless access to scada system
                                                     monitor, supervise and control the generation and
Operation and performance of the power Systems       transmission system as well as to cater for their
is mainly dependent on the efficiency of the         increasing sophistication in system operation and
SCADA system and the application functions           coordination. However the relay based system s
mounted on it for the power system analysis. The     continues to be utilized for all the major 22kv
paper examines the benefits of SCADA by              substation to provide remote monitoring and
applying web services and services and wireless      control facilities.
access to conventional SCADA systems. The            The SCADA plant monitoring systems operates as
terminals and RTUs are presently connected           a stand alone, autonomous systems,
through local area network (LAN). Distributed        As a stand alone, autonomous systems, as a stand
network protocol (DNP) is developed to be            alone, autonomous systems monitoring sensors
applied in the SCADA systems for increased           ,displaying data outputting controls, activating
reliability .This technology becomes an extremely    alarms and logging information to facilitate an
useful entity when the conditions in a process       optimize the plant process and ongoing
plant are harsh and the site is remote. Resources    operations. It shall be capable of polling,
for data communication are difficult to obtain       transmitting and receiving data, both analog and
under such kind of environment and a wireless        digital, at high rates of speed, using secure
channel communication through a cellular phone       digitizing protocols and error advance methods.
is an efficient and more practical solution.         Fetching system data (digital and analog) like
wireless access using GPRS is also high lightened    breaker statuses, voltages, currents, power factors,
in this paper.                                       frequency etc. These systems are primarily
                                                     comprised of computer systems, remote terminal
Key words: SCADA systems, WAP, GPRS, WAP             units and communication systems, and above this
security, fire walls, fire walls, RTU’S, HTML, and   the software which drives the SCADA
DNP.                                                 functionalities.
                                                     The WAP solution brings the content of HTML
1. Introduction to SCADA:                            applications to mobile devices. The user can
                                                     access public web services and corporate
Supervisory control was first introduced at          information using a WAP-enabled phone .the
Singapore in 1966, where a telephony based relay     WAP gateway transforms the information to a
was installed to provide remote monitoring and       format suitable for mobile networks and devices.
control facilities for the 66kv network and all      The content provider can also create WML
major 22kv substations. Then in 1979, with the       applications specifically for the mobile
introduction of a 230kv network, a computer          environment .the implementation of analytical
based SCADA systems equipped with automatic          software into the power system communication
generation control function was commissioned to      network gives a very useful and economical tool
                                                     to the design of an efficient and reliable
                                                     communication network for the SACDA system.
2. Scope of wap in the scada systems:                HTTP response (the web server perceives the
while process visualization through computer         gateway as a proxy server).
screens and local HMI interfaces tied to the         3. The gateway converts the HTTP response into a
different PLC’S is commonly used, a remote           WAP response for the mobile device.
handheld instrument is conveniently used that        The micro browser in the mobile terminal
could provide visualization and control signals in   interprets the response and displays it
the last few years, WAP allows internet access to    appropriately.
cell phones, PDAs and other low- computational       3. General architecture of the scada
–power devices. in addition, the light weight        system with wap:
WAP protocol has a layered architecture and is       SCADA system collects real-time data from field
designed to operate over a variety of wireless       devices from a control center. SCADA systems
services, including code division multiple access    compromise of Host, FEP, MMI (Local/remote),
(CDMA), cellular digital packet data, general        the application server and finally the
packet radio service (GPRS), and so on .based on     communication network. The SCADA kernel
internet standards such as HTTP, wap wireless        system running on the Host system stores the data
protocols requires transferring large amounts of     collected by FEP and provides data to MMI for
mainly text-based data. Fast growth of GSM           display and application server for further analysis.
wireless networks has opened a unique                The FEP interfaces with the Hardware devices
opportunity of data transfer. In may 2000 some of    (RTUs) in the field through appropriate
the world’s leading manufacturers (Nokia,            communication channels and fetches the required
Ericsson, and Motorola), have created WAP            field data and sends to the host. Host control the
(wireless application protocol), an open global      operation of FEP and MMI and logs the field data,
standard that introduces many advantages to          alarms and events for subsequent analysis.
industry and power engineering. Some of its          General architecture of the SCADA system is
salient features are:                                given in fig.3. Due to communications or
-it enables remote supervision and control of        equipment failure or other reasons. It is likely that
machinery and processes from a mobile phone.         the fetched data is erroneous. Application servers
Calls and SMS, alarms and warnings can be sent       are equipped with the software, which identifies
to the people in charge of machines/processes.       the bad data and corrects it. Also application
-it offers the operators greater freedom and         servers ta and sends to HOST. The are equipped
flexibility at work; jobs can be organized better,   with the software domain analysis. These
more efficient and cost-effective.                   programs are computationally necessitating and
-in a system with exiting SCADA (figure 2) it        thus generally loaded on the separate computer
brings real-time information to the mobile phones    system and not on the host so that the basic host
and PDAs using WAP technology. It upgrades the       functionality is not disturbed. Since the FEP is
exiting MMI and SCADA applications.                  fetching vital system data and the host is
The WAP standard consists of two essential           gathering and storing these data, there are hot
elements; an end-to-end application protocol and     stand by units to ensure the reliable and
an application environment based on the browser.     uninterrupted operation. There could be many
The application protocol is a communication stack    MMIs in the control Host controls the operation
embedded in each WAP-enabled wireless device         of FEP and MMI and logs center connected
(also known as the user agent). The server side is   through the LAN. Further there could be remote
defined as a WAP gateway which implements the        MMIs at the distant places from where system
other end of the protocol and communicates with      operators can do various studies. The MMI is
any WAP client.                                      provided with the Graphical user interface (GUI)
1. A mobile telephone sends WAP requests to a        to depict the field/substation diagrams and display
WAP gateway                                          the alarms and events. Real time data stored in the
2.The gateway, upon receiving a WAP request,         host system is displayed on these MMI substation
sends an HTTP request to a plain web server,         diagrams. MMI needs a configurator to draw the
which provides the content through a normal          field diagram for every application, define field
                                                     devices and assign to the GUI objects .

                                                  operational functions. In SCADA operation, all
                                                  outstations send its most current status and
                                                  information to the control centre master CPU for
                                                  processing. These data will basically include
                                                  digital data (switch gear on/off, alarm on/off) and
                                                  analogue data (feeder current in amperes,
                                                  transformer/switchgear output in volts).these data
                                                  are sent, through the communication network to
                                                  the master CPU running in the company control
                                                  centre, by the telemetry equipment installed at
                                                  various outstations. The data will be scanned and
                                                  analyzed by the system control software
Fig2: WAP SCADA used in industrial
automation systems

4. The SCADA System and Distributed
Network Protocol (DNP):
The major functions of the communication
network across a power supply company are to
channels for data processing on SCADA
(Supervisory Control and Data                     FIG 3: ARCHITECHTURE OF SCADA
Acquisition).automatic generation control and     USING WAP
scheduling, and for the distributed power plant
                       program to pick out any mismatch occurred at
                      system control engineer will be informed of the
                      alarm condition by the VDUs (visual the display
                      units) and instruments installed on the SCADA
                      system in a power distribution company
                      comprises a reasonably large communication
                      network. Each outstation represents the
                      communication node. All these nodes can be
                      connected together via different communication
                      links (as seen in the figure 4).
                      The connections of these nodes from
                      communication sub network main processor
                      (server) in the sub network which gives
                      commands to all clients connected in the sub
                      network. Network simulation software can be
                      applied to investigate different activities and
                      performance results of a SCADA system.
                      Distributed network protocol (DNP) is a standard
                      based communication protocol developed to
                      achieve interoperability among systems operating
                      in a process control environment.
                       DNP has the flexibility to support multiple
                      operating modes such as poll-response, polled
                      report-by-exception, unsolicited responses and
                      peer-to-peer. It permits multiple masters and
                      encourages distributed intelligence. The DNP
                      protocol stack rides on TCP/IP protocol suite in
                      order to transport the DNP traffic on the internet
                      network using Ethernet and token ring local area
                      network as the network infrastructure.
                      With emerging of the wireless application
                      protocol (WAP) in recent years, DNP functions
                      can be embedded on the WAP architecture such
                      that the DNP features and applications can be
                      accessed through wireless terminal unit. This
                      wireless application can be quite useful in a hard
                      to reach environment such as a power
5.utility of five layerd wap structure
The WAP protocol stack has five layers:               operators, and the functionality of the upper layers
Application, Session, Transaction, Security, and      of the WAP stack. The WTLS provides safe data
Transport. Each layer performs almost the same        transmission that could support services requiring
functions as the corresponding layers of the          a high level of security such as mobile e-
internet model with little or no difference.          commerce.
Wireless application environment:
The application layer consists of the wireless        Wireless Datagram Protocol:
application environment and user agents. The          The wireless Datagram Protocol transmits and
most common type of user agent in the WAP             receives to and from the user agents. The WDP
architecture is a browser meant to interpret          can exchange information with many types of
wireless markup language and WMLScript.               wireless data carrier technologies or “bearers.” It
User agents that endeavor to provide services         effectively hides the differences in bearer
beyond those of a browser generally take              technologies from the rest of the stack and
advantage of the WAP specification’s wireless         provides a common interface to the upper layer
telephony application features.                       protocols. Layers can function independently of
Wireless session layer:                               the underlying network and the wireless devices.
The wireless session protocol presents the            FIG5: FIVE LAYERED STACK OF
application layer with a way to uniformly receive     WAP
both      “reliable”    connection-oriented    and
“unreliable” connectionless transmissions. The
WSP facilitates transmission mechanisms such
      Providing HTTP functionality
      Enabling users to participate in long-live
           data transmission sessions
 Allowing a server application to determine
whether a client can support certain protocol
facilities and configurations ( this is known as “a
capability negotiation”)

Wireless Transaction Protocol:
The wireless transaction protocol handles requests
and responses to and from the user agent to the
application server. The WTP concentrates on
transaction services for online activities such as
web browsing. It is designed to decreases the
number of transaction phases that typical wired-
oriented protocols require.
Wireless Transport Layer Security:
The wireless transport layer security implements
many features to ensure secure data transmissions
and to protect the users, the network and service
6. Wireless access using gprs and                      FIG6: SCADA WITH GPRS
design of web services:                                TECHNOLOGY
The general packet radio system (GPRS) is anew
service that provides actual packet radio access
for mobile Global System for Mobile
Communications (GSM) and time division
multiple access (TDMA) users. The main benefits
of GPRS are that it reserves radio resources only
when there is data to send and it reduces reliance
on traditional circuit –switched network elements.
The increased functionality of GPRS will
decrease the incremental cost to provide data
services, an occurrence that will in turn, increases
the penetration of data services, among consumer
and business users. In addition, GPRS will allow
improved quality of data services as measured in
terms of reliability, response time, and features      The wireless access protocol (WAP) empowers
supported. The unique applications that will be        mobile users of wireless devices to easily access
developed with GPRS will appeal to a broad base        live interactive information services and
of mobile subscribers and allow operators to           applications from the screens of mobile phones.
differentiate their services. These new services       Services and applications include e-mail,
will increase capacity requirements on the radio       customer care, call management, unified
and base station subsystem resources. one method       massaging, weather and traffic alerts, news, sports
GPRS uses to facilitate the capacity impacts is        and information services, electronic commerce
sharing the same radio resource among all mobile       transactions and banking services, online address
stations in a cell, providing effective use of the     book and directory services, as well as corporate
scarce resources. In addition, new core network        intranet applications. WAP utilizes HTTP 1.1 web
elements are deployed to support the high rate of      servers to provide content on the internet or
data transfer more efficiently. In addition to         intranets, thereby taking advantage of existing
providing new services for today’s mobile user.        application development methodologies and
GPRS is important as a migration step towards          developer skill sets such as CGI, ASP, NSAPI,
third- generation (3G) networks. GPRS will allow       JAVA, AND Servlets. WAP defines an XML
network operators to implement ip-based core           (Extensible markup language) syntax called WML
architecture for data applications, which will         (wireless markup language). All WML content is
continue to be used and expanded upon for              accessed over the internet using standard HTTP
3Gservices for integrated voice and data               1.1 requests. To take advantage of today’s
applications in addition, GPRS will prove a            extremely large market penetration of mobile
testing and development area for new services and      devices, the user interface components of WML
applications, which will also be used in the           map well onto existing mobile phone user
development of 3G services.                            interfaces. This means end users can immediately
                                                       use WAP ENABLED mobile phones and
services without re-education. WAP specifications      can reach a wide variety of different wireless
enable products which standard internet                platforms in an efficient and useful manner.
technology to optimize content and air link            There are two data flows in the web services. The
protocols to better suit the characteristics and       static data, which is pictures, like single line
limitations of existing and future wireless            diagrams etc, which are depicted on the MMI
networks and devices. Since WAP transport is           screen. These screens are static in nature and are
based on IP, the WAP layered architecture              superimposed by the dynamic data. The dynamic
enables other services and applications to utilize     data are the measurements. Acquired by the
the features of the WAP stack through a set of         SCADA systems using remote terminal units
well defined interfaces Figure 6 shows GPRS            (RTU’s). After processing this data is stored in
based telemetry for SCADA systems. The GPRS            shared
enabled devices are generally configured to
operate as a TCP/IP terminal server linked to the               FIG7: ARCHITECHTURE OF
GPRS network via a modem. Two connections                             WEB SERVICE
were provided to the RTU:
     1. The main serial port to carry DNP3-                           APPLICATIONS
          based control traffic.
     2. a secondary serial port to permit remote
          control and configuration of the RTU
          itself.    For       providing     control
          programming environment, the core
          kernel was modified to handle the GPRS
          connection and ensure that the
          connection was continuously maintained
          (GPRS is promoted as an ‘always-on’
          service, but in reality, this is not quite
          The standard DNP3 protocol is in
          general preferred for connecting RTU’s
          to general SCADA systems. The DNP3
          packets received by the director from the
          RTU are wrapped in TCP/IP protocol           memory where the SCADA data is shared with
          and transmitted via the cellular modem       the web services. The static data is created using
          to the central SCADA system. Packets         configuration files which includes the pictures and
          arising from the Host are stripped of        the tags for getting the dynamic data. These
          TCP/IP and passed to the RTU. Simple         configuration files are converted into HTML and
          serial communications to and fro from        /or WML pages by HTML/WML converter and
          the secondary port are simply transferred    mixed with tag values (measurements) in the IIS
          as it is.                                    server and floated as web pages/WML pages on
The WTP operates efficiently over secure or non        the internet using SOAP protocol. Thin client and
secured wireless diagram networks. This gives a        the WAP phones request for the pages and get the
flexibility to offer the WAP service to the            static as well as dynamic information for the first
SCADA system based on the security level               time and then only the dynamic data is updated
requirement. For any wireless connection request,      SOAP protocol.
the WSP will be the layer to deal with. This layer     7. The challenges of wireless scada
establishes relationship between the SCADA             systems:
system application, and the WAP server. The            There are many parameters of wireless SCADA
WSP uses the services of the WTP for reliable          systems which should be taken care of to ease the
transport to the estimation proxy gateway. The         work of users by providing reliable, quick and
WAE allows the establishment an interoperable          virus free software. Thus these are the
environment that will allow operators and service      distinguishing factors for users to make a choice
providers to build applications and services that      between various products available.
Thin client support:
Thin client support means the MMI runs on any          user would like to choose the data he wants to
computer system, which runs only internet              access, certainly not interested in highly complex
browser (in addition to operating system) with the     navigation. To meet this requirement, a
network connectivity. No additional application        configurator is provided to configure the data to
software is to be installed on the system. This is     be accessed in a hierarchical fashion giving the
very convenient way of installing MMI on               flexibility to choose on the mobile but customize
LAN/WAN. This is achieved by using VML [7],            the level of navigation.
which is a derivative of SGML. VML objects are         Also the alarms can be configured to send to
embedded in standard HTML pages.                       designated mobile phones as SMS messages.WAP
Refreshing GUI:                                        publisher is an ASP [10-12] application to create
Normally each request of HTML fetches new              WML pages for access through mobile phones
HTML page on the browser. To update the time           and PDAs. The WAP publisher dynamically
varying data, the MMI screen needs to be updated       generates the WML pages. this application can be
regularly. This causes flickering of the screen,       built using Microsoft Mobile tool kit and the
which is undesirable. To avoid this only updated       rending of pages is based on the hardware device
data is obtained, not the complete graphics like       making the query. The each query on URL
single line diagrams, from host and only effects of    displays all available WAP tag groups of the
data changes are represented on the screen. This is    current project. The query on WAP tag group
achieved by fetching data using web services.          displays the list of tag groups. If the tag group
                                                       contains only tags, the web service is queried and
VML objects are animated locally on the browser .
                                                       current tag data is displayed on the device. This
Data updates:                                          facilitates easy navigation and reduces the
Since the real time data is continuously varying, it   network traffic. The predefined alarms will be
is always desirable to have a quicker data update      reported as SMS messages to appropriate mobile
on the MMI. This update is limited on the browser      phones.
by data volume and the network bandwidth. Web
MMI achieves this objective by limiting the            9. Improvement of web services and
network traffic to essential data. Even on internet,   wap from customers prospective:
the refresh frequency of few seconds can be            Several improvements and new functionalities are
achieved, for the example screen data, with the        suggested      for   improving      the    existing
usual bandwidth of the 56 kbps.                        functionalities of WAP from users prospective
                                                       *Proper Alarm Identification: alarms are
Firewalls:                                             generated whenever the value of the analog tags
Security has become a major concern for the            crosses the upper or lower limit. They are logged
organizations having the vital data. The firewalls     in the alarm table where the operator can
are built to secure the data and restrict              acknowledge them. Unacknowledged alarms are
unauthorized access to the data servers. System        of different colors (usually bright) to distinguish
administrators would not like to open additional       them from the acknowledged alarms.
ports for the applications accessing data through      *New Data Collection Engine for OPC servers
EXTRANET/ INTERNET. Web services use                   should be provided to open the possibility for
SOAP, which operates on HTTP port itself               further implementation of other Data collection
eliminating the need to compromise on security         Engines by third parties.
policies.                                              *New Multi-language option should be provided
8. Ap publisher:                                       which allows easy translation to other languages.
Access to SCADA data on the mobile (WAP                *New Configuration and Maintenance tools are
enabled), is a highly desirable feature for the        required to be provided which other system
modern executives. However, the volume of data         integrators to use product in their own
that can be displays on the mobile screen is           applications.
restricted by the size of the screen. Even though
*An Open Source Software instead of commercial        WTAI and other WAP resources can be applied in
licensed software will take the technology into the   the power system SCADA application. This user
people and lower price of software licenses and       agent sends request to the WAP gateway. The
wide range of free development tools encourages       wap gateway will send request to SCADA server
many small industries to use SCADA.                   after encoding the user agent request. This
*Microprocessor independent. A lower hardware         software will be running in a mobile device to
requirement allows multi platforms (not just Intel    connect to the desired system through intranet or
microprocessors). Including embedded devices.         internet network carrying out supervisory tasks as
*operating system independent software should be      well as remote control functions. It means that
developed such that it can be run on all the          SCADA database can be transferred to the mobile
computers the source code written in Java allows      environment through the WAP service. Further
running it on different operating systems.            the firewall security should be constantly revised
*Security: proper security should be provided for     to secure the data.
WAP enabled devices. So the software should be
resistive to any hacking threats.                     References:
10. Conclusion:                                       [1] “Devoloping and Defining Basic SCADA
This paper demonstrated the efficient application     System Concepts” by john D.Mcdonald, Senior
of web services in the SCADA systems.                 Member, IEEE
Development of web MMI and WAP publisher              Advanced Control Systems, Norcross, Georgia
along with the configurator and its use in the real   [2] Qiu B., and Gooi H.B., “web-based SCADA
time SCADA systems clearly demonstrates its           Display System (WSDS) for Access via
utility in the real time system for various           Internet”,IEEE Transactions on power system,
purposes. This provides highly desirable features     vol. 15, no. 2, May 2000, pages 681-686.
for modern executives so that they can avail the      [3] “Advanced SCADA Concepts” by Samuel
vital data at any place in the world without          C.Sciacca and Wayne R. Block, Published by the
carrying much of computer hardware and                IEEE CS and IEEE communication society.
software. The WAP architecture and the DNP            [4] Zecevic Goran, “Web based interface to
protocol in SCADA system are discussed. The           SCADA system”, proceedings of international
WAP framework provides an easy access and             conference on power system technology
wireless communication environment, it is             (POWERCON 98).vol.2, 18-21 Aug 1998,pages
advantageous to incorporate this infrastructure       1218-1221.
into the SCADA system.                                [5] Article on “SCADA and IP”, by ROBERT
The interfacing to the SCADA application              H.MCCLANAHAN, IEEE industrial applications
program such as the communication between the         magazine, march-April 2003
WAP script and the c++ programs in an object -        [6]IEEE Tutorial Course on fundamentals of
oriented programming SCADA system should be           supervisory Systems, 91EH0337-6 PWR
optimized. The low transfer rate and long latency
in a mobile network must be taken care of. The
WAP protocol should be looked into to solve this
issue. The deployment of a suitable packet size in
the WDP layer is important since the SCADA
system operation may require a long message
packet. This depends on the configuration of the
communicating RTU. The security issue during
the WAP service transaction can be stored out
through the WTLS layer. The WAP proxy server
can also provide the security protection for the
network     end-to-end     communication.      The
emerging of the new protocol such as WEXE help
solve some of the harsh issues in a proper manner.
A user agent complied by WML, WML script,

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