Practical_modern_SCADA_protocols_-_dnp3,_60870-5_and_Related_Systems

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326 Practical Modern SCADA Protocols: DNP3, 60870.5 and Related Systems 12.7 Collisions You should recognize that collisions are a normal part of a CSMA/CD network. The monitoring and detection of collisions is the method by which a node ensures unique access to the shared medium. It is only a problem when there are excessive collisions. This reduces the available bandwidth of the cable and slows the system down while retransmission attempts occur. There are many reasons for excessive collisions and you will investigate these shortly. The principle of collision cause and detection is shown in the following diagram. Figure 12.7 CSMA/CD collisions
Ethernet and TCP/IP networks 327 Assume that both node 1 and node 2 are in listen mode and node 1 has frames queued to transmit. All previous traffic on the medium has ceased ie there is no carrier, and the interframe gap from the last transmission has timed out. Node 1 now commences to transmit its preamble signal, which immediately commences to propagate both left and right on the cable. At the left end, the termination resistance absorbs the transmission, but the signal continues to propagate to the right. However, the MAC sublayer in node 2 has also been given a frame to transmit from the LLC sublayer, and since the node ‘sees’ a free cable, it too commences to transmit its preamble. Again, the signals propagate on to the cable, and some short time later they ‘collide’. Almost immediately, node 2’s transceiver recognizes that the signals on the cable are corrupted, and the logic incorporated on the NIC asserts a collision detect signal. This causes node 2 to send a jam signal of 32 bits of random data, and then stop transmitting. In fact, the standard allows any data to be sent as long as, by design, it is not the value of the CRC field of the frame. It appears that most nodes will send the next 32 bits of the data frame as a jam, since that is instantly available. This jam signal continues to propagate along the cable, as a contention signal since it is ‘mixed’ with the signal still being transmitted from node 1. Eventually, node 1 recognizes the collision, and goes through the same jam process as node 2. You can see from this that the frame from node 1 must be at least twice the end-to-end propagation delay of the network, or else the collision detection will not work correctly. The jam signal from node 1 will continue to propagate across the network until absorbed at the far end terminator, meaning that the system vulnerable period is three times the end-to-end propagation delay. After the jam sequence has been sent, the transmission is halted. The node then schedules a retransmission attempt after a random delay controlled by a process known as the truncated binary exponential backoff algorithm. The length of the delay is chosen so that it is a compromise between reducing the probability of another collision and delaying the retransmission for an unacceptable length of time. The delay is always an integer multiple of the slot time. In the first attempt, the node will choose, at random, either one or zero slot times delay. If another collision occurs, the delay will be chosen at random from 0, 1, 2 or 3 slot times, thus reducing the probability that a further collision will occur. This process can continue for up to 10 attempts, with a doubling of the range of slot times available for the node to delay transmission at each attempt. After ten attempts, the node will attempt 6 more retries, but the slot times available for the delay period will remain as they were at the tenth attempt. After 16 attempts, it is likely that there is a problem on the network and the node will cease attempting to retransmit.
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Practical Modern SCADA Protocols: D
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Practical Modern SCADA Protocols: D
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Contents Preface ..................
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Contents vii 12.6 Frame reception .
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Preface ix Chapter 3: Open SCADA pr
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1 Introduction Objectives When you
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Introduction 3 Figure 1.2 PC to IED
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Introduction 5 The interconnection
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Introduction 7 a number of sub-path
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Introduction 9 The Internet protoco
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Introduction 11 Outside the utiliti
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Fundamentals of SCADA communication
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Key features of SCADA software incl
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2.2.2 Control processor unit (or CP
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2.5.2 Multi-point architecture (Mul
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2.6 Communication philosophies Fund
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Pin 8 - Data carrier detect (DCD) F
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2.7.6 Synchronous communications 2.
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The two most common modes of operat
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2.8.3 Error control/flow control Fu
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3 Open SCADA protocols DNP3 and IEC
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3.2.2 DNP 3.0 and IEC 60870 protoco
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4.2 Interoperability and open stand
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Preview of DNP3 69 The DNP3 User Gr
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Preview of DNP3 71 The capability t
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5 Fundamentals of distributed netwo
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Fundamentals of distributed network
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5.3.6 Full-duplex procedures Fundam
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The message sequences are shown in
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These rules are illustrated in the
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Freeze functions are typically used
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6 Advanced considerations of distri
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Advanced considerations of distribu
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6.2 Interoperability between DNP3 d
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6.3.2 Data classes and events Advan
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Recommendations: 6.3.9 Multiple obj
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6.3.15 Time-tagged binary input eve
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Preview of IEC 60870-5 171 7.2 Stan
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Preview of IEC 60870-5 173 Under IE
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Preview of IEC 60870-5 175 over cor
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8 Fundamentals of IEC 60870-5 8.1 T
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Fundamentals of IEC 60870-5 179 8.1
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8.1.9 IEC 60870-5-101 1995 Fundamen
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Fundamentals of IEC 60870-5 183 pro
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Fundamentals of IEC 60870-5 185 MAS
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8.4 Data link layer Fundamentals of
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8.4.2 Order of information Fundamen
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8.4.5 Unbalanced and balanced trans
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Fundamentals of IEC 60870-5 193 Sta
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Station/link initialization, balanc
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Fundamentals of IEC 60870-5 197 The
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Fundamentals of IEC 60870-5 199 To
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Function codes from secondary stati
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Fundamentals of IEC 60870-5 203 is
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The following notes apply to these
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Fundamentals of IEC 60870-5 207 Typ
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Fundamentals of IEC 60870-5 211 Whe
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Fundamentals of IEC 60870-5 215 to
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Fundamentals of IEC 60870-5 217 Mas
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Fundamentals of IEC 60870-5 219 Qua
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Fundamentals of IEC 60870-5 221 Key
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Fundamentals of IEC 60870-5 223 SVA
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Fundamentals of IEC 60870-5 225 Key
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Fundamentals of IEC 60870-5 227 DCO
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8.6.4 Qualifier information element
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Key - QOC Qualifier of command QU Q
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Fundamentals of IEC 60870-5 233 SCQ
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Fundamentals of IEC 60870-5 235 LOF
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Fundamentals of IEC 60870-5 237 FBP
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Fundamentals of IEC 60870-5 239 In
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Fundamentals of IEC 60870-5 247 Val
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Type 11 Measured, scaled value Fund
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Fundamentals of IEC 60870-5 255 Val
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Type 20 Packed single-point with st
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Fundamentals of IEC 60870-5 259 Pro
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Page 291 and 292: Fundamentals of IEC 60870-5 275 Typ
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Page 327 and 328: 10.2 Which one will win? Difference
Page 329 and 330: Intelligent electronic devices (IED
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Page 335 and 336: Ethernet and TCP/IP networks 319 Th
Page 337 and 338: Ethernet and TCP/IP networks 321 Fi
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Page 349 and 350: 12.11.8 Fast Ethernet Ethernet and
Page 351 and 352: 12.12 TCP/IP Ethernet and TCP/IP ne
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Page 365 and 366: 13 Fieldbus and SCADA communication
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Applications of DNP3 and SCADA prot
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PDS 500 Data Map Applications of DN
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16 Future developments Objectives W
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Appendix A Glossary 3GPP 10Base2 10
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Appendix A: Glossary 395 ATM Attenu
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Appendix A: Glossary 397 Capacitanc
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Appendix A: Glossary 399 Decibel (d
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Appendix A: Glossary 401 ESS Etherl
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Appendix A: Glossary 403 I/O addres
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Manchester encoding Appendix A: Glo
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Appendix A: Glossary 407 Packet PAD
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Appendix A: Glossary 409 RFI Ring R
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Appendix A: Glossary 411 TDMA TDR T
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Appendix A: Glossary 413 X.25 CCITT
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Appendix B: Implementers of DNP3 41
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Appendix B: Implementers of DNP3 41
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DNP3 device profile Appendix C: Sam
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Appendix C: Sample device profile d
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Software setup Appendix D: Practica
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Appendix D: Practicals 431 1. Set u
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Objectives • To show how a basic
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Implementation/setting up TCP/IP Cl
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Appendix D: Practicals 437 Click on
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Appendix D: Practicals 441 Now rese
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Appendix D: Practicals 443 Practica
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Appendix D: Practicals 445 This sho
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Appendix D: Practicals 447 Once you
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IMPORTANT NOTICE: Appendix D: Pract
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Appendix D: Practicals 451 (This is
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Appendix D: Practicals 453 PRACTICA
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Click on the Diags button and the f
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Appendix D: Practicals 457 The scre
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Appendix D: Practicals 459 Assume t
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Appendix D: Practicals 461 Problem
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Network Loading Assumptions Item Da
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2. IEC 60870-5-101 Packet Analysis
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3.1.1.1.1 Appendix D: Practicals 46
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Appendix D: Practicals 469 Valid Ca
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3.1.1.1.7 Type 14 INFORMATION OBJEC
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Appendix D: Practicals 473 3.1.1.1.
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Appendix D: Practicals 475 QDS Qual
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Appendix D: Practicals 477 7 6 5 4
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3.1.1.1.11 Communication 1 Appendix
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Communication 1 Answer Appendix D:
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CITECT PRACTICAL For Citect Version
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Appendix D: Practicals 485 Next cli
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Appendix D: Practicals 487 (3) Defi
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Appendix D: Practicals 489
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Appendix D: Practicals 491 (4) Crea
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Appendix D: Practicals 493 Use the
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Appendix D: Practicals 497 When fin
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Appendix D: Practicals 499 What is
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Communication 2 05640DC405001A00637
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05640DC405001A006378C6C601010200003
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Appendix D: Practicals 505 What are
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Appendix D: Practicals 507 01 01 01
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Appendix D: Practicals 509 E2 81 00
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Appendix D: Practicals 511 At fist
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Appendix D: Practicals 513 Then rem
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Appendix D: Practicals 515 The next
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Packet Interpretation Practical App
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056408C40300A200EA80C5C5171E4405641
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Appendix D: Practicals 521 Communic
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05640DC405001A006378C6C601010200003
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Appendix D: Practicals 525 What is
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01 01 01 01 01 01 01 crc:BB crc:C3
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Appendix D: Practicals 529 Read Dat
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Index 531 Carrier sense with multip
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Index 533 support for protocol, 310
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Index 535 process related, 220 bina
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Index 537 signal quality detector,
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