QoS, Security and Energy Requirements in Wireless Automation ...
QoS, Security and Energy Requirements in Wireless Automation ...
QoS, Security and Energy Requirements in Wireless Automation ...
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<strong>QoS</strong>, <strong>Security</strong> <strong>and</strong> <strong>Energy</strong> <strong>Requirements</strong> <strong>in</strong><strong>Wireless</strong> <strong>Automation</strong> NetworksMikael BjörkbomTKK | Control Eng<strong>in</strong>eer<strong>in</strong>g
Contents• Quality of Service• What? – What service quality does a wireless automationsystem need?• How? – <strong>QoS</strong> techniques• <strong>Security</strong>• Why? – Why bother when there are communication <strong>and</strong>computational constra<strong>in</strong>ts• How? – How to do it lightweight• <strong>Energy</strong>• What? – <strong>Energy</strong> constra<strong>in</strong>ts• How? – How to cope with theseTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>2
Introduction• <strong>QoS</strong> is needed to obta<strong>in</strong> a good wireless automationsystem• Real-time automation• Manages the network, such that the application requirementsare satisfied• <strong>Security</strong> is needed to ma<strong>in</strong>ta<strong>in</strong> a work<strong>in</strong>g automationsystem• Safe, dependable automation• <strong>Energy</strong> for long lifetime of the application• Batteries, energy sources• Conserve energyTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>3
QUALITY OF SERVICETKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>4
Introduction• “<strong>QoS</strong> is the application experienced quality of the datatransportation <strong>in</strong> terms of some parameters”• <strong>Wireless</strong> network issues <strong>Automation</strong> requirements• <strong>QoS</strong> difficult <strong>in</strong> wireless networks• Shared media, noise<strong>Wireless</strong> Network<strong>Wireless</strong><strong>Automation</strong>:- Vary<strong>in</strong>g delay- Packet lossTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>5
• What it is not<strong>QoS</strong> <strong>in</strong> <strong>Wireless</strong> <strong>Automation</strong>• High throughput• Large data streams• Average availability• What it is• Many small packets (~10-50 bytes)• S<strong>in</strong>gle measurements• Control comm<strong>and</strong>s• Delivered on time• Preferably without loss, Constant availability• If loss• No large gaps!• Communication dependability, reliabilityTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>6
Or then...• If process is slow• The dynamics of the network is negligible• Only successful packet delivery is needed• Data queries, monitor<strong>in</strong>g, ma<strong>in</strong>tenance• For service man with h<strong>and</strong>held device• Usually delay tolerantTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>7
Basic <strong>QoS</strong> Measures• Packet loss• Low bit error rate, physical level• MAC protocol• Avoid dropp<strong>in</strong>g packets• Avoid dropp<strong>in</strong>g consecutive packets• Some packets may be dropped on purpose• Old <strong>in</strong>formation• Redundant <strong>in</strong>formation• Average, Maximum Delay• Affects control performance: ω c < 1/T d• Delay Jitter• Variation <strong>in</strong> delayTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>8
More <strong>QoS</strong> Measures• Cont<strong>in</strong>uous operation• If network down orcongested, real-timerequirements are not met• Plant must be brought toa safe state• MTBF/Failure length• <strong>Energy</strong> consumption• Node lifetime• Network lifetimeTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>9
Network Related <strong>QoS</strong> Measures• Robustness to abnormal traffic• Network setup• Node jo<strong>in</strong> time• Node depart time• Network recovery time• Recovery to normal operation after a disruptive event• Topology changes, obstacles• Communication overhead• Protocol overhead• Rout<strong>in</strong>g ma<strong>in</strong>tenance, robustness• Issues of protocol designTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>10
Sensor Network <strong>QoS</strong> Measures• Number of active sensors/nodes• Data accuracy• Time-synchronization accuracy• Network scalability• Throughput• Reliability• Interference tolerance• <strong>Security</strong>• Mobility• Coord<strong>in</strong>ation effectivenessTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>11
Time-Synchronization• Time-synchronization of nodes used <strong>in</strong> all wirelessautomation protocols• Control system requirement• TDMA MAC• Transmission slots, reliable communication• Tight marg<strong>in</strong>s• ISA100.11a: 12 ms for packet <strong>and</strong> ACK• Data timestamp• Application needs to know when data was recorded• Synchronization of actions• Sens<strong>in</strong>g at same time• Actuator apply comm<strong>and</strong> at certa<strong>in</strong> timeTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>12
• Depends on applicationRequired <strong>QoS</strong>• Guaranteed service prefered over best effort• Monitor<strong>in</strong>g, Sensor Networks, Build<strong>in</strong>g automation• Lossless packet delivery• Sources to s<strong>in</strong>k• <strong>Energy</strong> consumption• Military• High security• Fault tolerant• Industry automation• Real-time requirements• Computation, Transmission• No large gapsTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>13
Delay Jitter – Control System Stability• Variation <strong>in</strong> delay• Problematic for control systems• Z-transform: z -d = constant delay• Jitter marg<strong>in</strong>δ max• The additional (vary<strong>in</strong>g) delay acontrol system can tolerate• 0 ≤δ( t)≤δmax• Stable ifMagnitude (dB)151050-5-10-15-20-25-30Complementary sensitivity function <strong>and</strong> 1/(δ max ω) for δ max= 0.5KLT+PID w/o filter1/(δ max ω)KLT+PID w. filter10 -4 10 -2 10 0 10 2Frequency rad/s( ω) ( ω)( ) ( )P j C j 1< , ∀ω∈ 0, ∞+ P jω C jω δ ω1maxTKK | Control Eng<strong>in</strong>eer<strong>in</strong>g[ ]More on this<strong>in</strong> a laterlectureAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>14
Alarm shower• A fault causes abnormal behaviour• Which causes alarms• Which causes alarms...• Large number of alarms must be communicated• Most of them are superfluous• The right must quickly be communicated• Priorization• Normal control communication must still stay operation• Guarantee stability of plant• Current st<strong>and</strong>ards transmit urgent data on CSMA slots• Can transmit immediately• Alarm shower -> all alarms collide?TKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>15
<strong>QoS</strong> Methods• Some over-provision<strong>in</strong>g• B<strong>and</strong>width constra<strong>in</strong>ts• Redundancy• Many sensors, nodes• Multipath rout<strong>in</strong>g• Schedul<strong>in</strong>g/Coord<strong>in</strong>ation of actions• Medium Access Control• TDMA, FDMA• Causes most of the communication delay• Most important for wireless control system <strong>QoS</strong>TKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>16
IEEE 802.11 MAC• Po<strong>in</strong>t Coord<strong>in</strong>ation Function (PCF)• AP polls other nodes, ”TDMA”• Contention Free Period• More controlled delay <strong>and</strong> delay variation• Enhancements IEEE 802.11e• Shedul<strong>in</strong>g• Distributed Coord<strong>in</strong>ation Function (DFC)• CSMA/CA• Ad-hoc network<strong>in</strong>g• Mostly usedContention free period Contention periodBeacon(CSMA/CA)TKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>17
802.11 Medium Access Control• Carrier Sense Multiple Access with CollisionAvoidance (CSMA/CA)• Less reliable than wired• S<strong>in</strong>ce own transmission covers other transmission signals• Hidden term<strong>in</strong>als problem• Request To Send (RTS) – Clear To Send (CTS)TransmitterReceiverHiddenterm<strong>in</strong>alTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>18
IEEE 802.11 <strong>QoS</strong>• Requested <strong>QoS</strong>• Priority• Contention – Contention free• Only with PCF, best effort with DCFTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>19
IEEE 802.11 PriorityShort Inter Frame Spaces (SIFS)• Highest priority• ACK...• Transmitted earlier on network idle period• PCF IFS (PIFS)• Communication under PCF• DCF IFS (DIFS)• Lowest priority• Compet<strong>in</strong>g under DCFPrevious frame SIFS PIFS DIFSIdle until transmission beg<strong>in</strong>sTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>20
<strong>QoS</strong> extensions to IEEE 802.11• IEEE 802.11e• Hybrid Coord<strong>in</strong>ation Function• Service classes• Different priority classes of messages• User priority• 0-7, access priority• Traffic specification• 8-15, TSpecTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>21
Bluetooth <strong>QoS</strong>• Poll<strong>in</strong>g• Two l<strong>in</strong>k types depend<strong>in</strong>g on prefered service• Asynchronous Connectionless• Max. 721 kbit/s asymmetric• For data• Synchronous Connection Oriented• Fixed 64 kbit/s throughput• For voiceTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>22
TDMA• Used <strong>in</strong> wireless automation st<strong>and</strong>ards• <strong>Wireless</strong>HART, ISA100• TDMA+FDMA, (Time/Frequency slots)• Reliable <strong>and</strong> robust• Quaranteed timeslot for transmissions• Can utilize full b<strong>and</strong>width without collisions• Sleep periods between transmissions (saves power)• Timeslot disadvantages• Cannot send immediately• Must synchronize the wakeup <strong>and</strong> sampl<strong>in</strong>g such that ready tosend at own timeslot• Measurements from different times• Time-synchronization must be accurateTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>23
<strong>QoS</strong> Difficulties• Multiple access media• IEEE 802.11 mostly DCF used/implemented• Distributed system• <strong>Energy</strong>, Computational constra<strong>in</strong>ts• The <strong>QoS</strong> protocols must be simple (signal<strong>in</strong>g + computation)• Vary<strong>in</strong>g environment• Signal fad<strong>in</strong>g, <strong>in</strong>terference• Nodes go to sleep, faults• => Nodes temporarily unavailable• Periodic <strong>and</strong> event driven communication• Alarm/event shower• Sometimes <strong>QoS</strong> is not metTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>24
SECURITYTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>25
<strong>Security</strong>• Focus on <strong>Wireless</strong> security• Communication is <strong>in</strong> the air• Anybody can listen• Anybody can <strong>in</strong>terfere• In wired systems eavesdropp<strong>in</strong>g is harder• <strong>Automation</strong> system must operate safely• Even under malicious/un<strong>in</strong>tended attacks• Generally <strong>in</strong> automation: secure access from <strong>in</strong>ternet• Special security requirements• Short packets• Low communication <strong>and</strong> computation overheadTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>26
<strong>Security</strong> Threats• Eavesdropp<strong>in</strong>g• Why care, it’s only process data?• Tak<strong>in</strong>g control of automation system• Injektion of harmfull messages• Rout<strong>in</strong>g disruption• Constantly transmitt<strong>in</strong>g/Intentionally collide• Virtual jamm<strong>in</strong>g• Communication jamm<strong>in</strong>g / DoS attacks• Route request• Denial of sleep attackTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>27
Topology related, Sensor Network• In sensor networks topology may be important• Blackhole, Wormhole• Sybil nodeABABBlackholeWormholeCABA,B,CSybil nodeY = mean(A, B, C, D)DTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>28
Secure Communication• Physical security• Authentication• Semantic securityTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>29
Physical security• Undetected communication• Seems like noise• Jamm<strong>in</strong>g/Interference resistance• Techniques• Spread Spectrum communication• Frequency hopp<strong>in</strong>g• UWBTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>30
Authenticat<strong>in</strong>g• Access control, node authenticaton• Only messages from authenticated nodes are accepted• Authentication/Sign<strong>in</strong>g of messages is also needed• Verify that the message has not been tampered with• Authentication methods• Message Authentication/Integrity Codes (MAC/MIC)• Sign<strong>in</strong>g with Public / Private KeyTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>31
Communication Encryption• Semantic security• Message unreadable by third party• Confidentiality: The communication is secret/encrypted• More computation is needed at the nodes toencrypt/decrypt the messages• Encryption methods• WEP, SSH, SSL, IPSec: Too heavy-weightTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>32
Keys• How to manage the keys?• Key<strong>in</strong>g mechanism• Create/Destroy• Distribute• Change• T<strong>in</strong>yPKKeys Benefits CostsGlobal Simple Not robust to nodecompromisePer-l<strong>in</strong>k/nodeIEEE 802.15.4GroupTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gGraceful degradation,No passiveparticipationGraceful degradation,Passive participationKey distributionprotocolKey distributionprotocolAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>33
T<strong>in</strong>ySec• <strong>Security</strong> module for T<strong>in</strong>yOS• Optimised for motes• Low computation <strong>and</strong> communication overhead• Easy to use: add one l<strong>in</strong>e to the makefile• T<strong>in</strong>ySec-Auth: Authentication only• T<strong>in</strong>ySec-AE: Authentication <strong>and</strong> EncryptionDest AM Len Data MACT<strong>in</strong>ySec-Auth packet formatDest AM Len Src Ctr Data MACT<strong>in</strong>ySec-AE packet formatTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>34
Message Authentication Codes• T<strong>in</strong>ySec uses MAC for authentication• Secret key• Compute MAC with key• Add MAC result to the end of packet• Receiver can verify MAC us<strong>in</strong>g public keyTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>35
Encryption• Only the data is encrypten <strong>in</strong> T<strong>in</strong>ySec• No decryption needed for rout<strong>in</strong>g• T<strong>in</strong>ySec uses Initialisation Vectors for encryption• Encryption of same message twice, different results• Othervise: easy to decrypt yes/no messages• Different IV for every packet• Message encryption <strong>in</strong>itialisation with IV• Send IV with message (T<strong>in</strong>ySec: packet headers)• Receiver can decrypt with public key <strong>and</strong> IVTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>36
Other <strong>Security</strong> Tasks• Intrusion detection• Monitor that neighbour<strong>in</strong>g nodes work as expected• Forward<strong>in</strong>g messages• Transmission pattern• F<strong>in</strong>d <strong>and</strong> Isolate rogue nodesTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>37
ENERGY REQUIREMENTSTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>38
Power consumption <strong>and</strong> lifetime• <strong>Wireless</strong> sensor nodes equipped with limited powersource• No use <strong>in</strong> wireless if they have wired power(?)• Physical size <strong>and</strong> cost constra<strong>in</strong>ts directly affectenergy available• Power sources• Battery• Solar cells• RF power<strong>in</strong>g• <strong>Energy</strong> harvest<strong>in</strong>gTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>39
Microsensors• Microelectromechanical (MEMS) sensors:etch<strong>in</strong>g process used to carve out t<strong>in</strong>ymechanical structures from silicon• Benefits:• Small, low energy consumption• Cheap to manufacture• Read-out electronics etc. (transistors) onsame chip• Example: micromechanicalgyro/accelometer• ESP system <strong>in</strong> cars• Adaptive cruise controlA schematic of MEMS accelerometer(Ville Kaajakari)• Reduces energy requirements! Micromechanical gyro(VTI Technologies)TKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>
Communication <strong>and</strong> Sleep<strong>in</strong>g• Sens<strong>in</strong>g, data process<strong>in</strong>g <strong>and</strong> communication consumepower:• Maximum energy consumed <strong>in</strong> data transmission <strong>and</strong> reception• Data process<strong>in</strong>g consumes much less power→ local data process<strong>in</strong>g rather than transmitt<strong>in</strong>g raw data• Sporadic sens<strong>in</strong>g may consume less power than constant eventmonitor<strong>in</strong>g• Sleep mode <strong>and</strong> wake-up radio (e.g. S-MAC)• Only wake up for a short period to communicate to save power• Node can not be contacted if radio is sleep<strong>in</strong>g• <strong>QoS</strong> when node is sleep<strong>in</strong>g?TKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>
Computation Strategy• Onl<strong>in</strong>e vs. offl<strong>in</strong>e/offnetwork• Computation <strong>in</strong> nodes saves energy• But does it need much communication/synchronization of data?• Centralized computation can be more effective• Is the computation power enough• Homogeneous devices vs. network consist<strong>in</strong>g of a variety ofdifferent devices• Some nodes may compute more than others or act as gatewayto long-range data communication• Affects robustness <strong>and</strong> capacity of networkTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>
• MAC protocols:• SMACS <strong>and</strong> EAR:MAC <strong>Energy</strong> Examples• Wake-up dur<strong>in</strong>g communication phase, radio off while idle• Pairwise, network-wide synchronization not necessary• Perform well <strong>in</strong> static networks• Has to wait to the wake phase to transmit• Hybrid TDMA/FDMA:• TDMA m<strong>in</strong>imizes transmit on-time, but high time synch. costs• Static TDMA waste b<strong>and</strong>width if noth<strong>in</strong>g to send• Hybrid TDMA-FDMA scheme with optimum number ofchannels to give lowest system power consumption• CSMA:• Constant listen periods (consumes power!!)• Adaptive to traffic loadTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>
Sectors for Improvement• CPU• Dynamic voltage scal<strong>in</strong>g <strong>and</strong>• Dynamic frequency scal<strong>in</strong>g to reducepower consumption by the CPU.• Hardware• Dedicated computation hardware such asFFT circuits to optimize computations<strong>in</strong>stead or us<strong>in</strong>g general purposeprocessors.• Radio• Duty cycle to power off the radio.• Reduc<strong>in</strong>g startup time of radio: improvephase locked loop <strong>in</strong> the frequencysynthesizer.• Transmit power control.• Signal process<strong>in</strong>g• Data aggregation to reduce transmissionof redundant <strong>in</strong>formation.• L<strong>in</strong>k layer• Bit error rate control. Cod<strong>in</strong>g techniques.• Adaptive error correction.• Network• <strong>Energy</strong> efficient network protocol, such asLEACH (Low <strong>Energy</strong> Adaptive Cluster<strong>in</strong>gHierarchy) [7].• Efficient rout<strong>in</strong>g• Cluster<strong>in</strong>g• Software• Power aware software reducescomputations if power is scarce.• <strong>Energy</strong> efficient coded software isobta<strong>in</strong>ed by us<strong>in</strong>g <strong>in</strong>structions <strong>and</strong>algorithms that takes less energy.• OS• Sleep modes. The OS controls thesleep/wake state, voltage <strong>and</strong> frequencyscal<strong>in</strong>g <strong>and</strong> other power sav<strong>in</strong>g modes ofthe node.• System• Distributed computations allow longerlatency per computation, thus decreas<strong>in</strong>gthe required CPU frequency.• System level coord<strong>in</strong>ation <strong>and</strong>optimization.TKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>45
Tradeoff<strong>QoS</strong><strong>Energy</strong><strong>Security</strong>TKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>46
Conclusions• Quality of Service• What: Delay, Packet loss...• How: Design MAC• <strong>Security</strong>• Why: <strong>Wireless</strong> automation system <strong>in</strong>tegrity• How: Authentication, Encryption, T<strong>in</strong>ySec• <strong>Energy</strong>• What? – Limited energy <strong>and</strong> therefore limited capacity• How? – <strong>Energy</strong> sources, sleep, energy awareTKK | Control Eng<strong>in</strong>eer<strong>in</strong>gAS-74.3199 <strong>Wireless</strong> <strong>Automation</strong>47