Mobile Wireless Networking Wireless Sensor Networks

Mobile Wireless Networking The University of Kansas EECS 882 Wireless Sensor Networks James P.G. Sterbenz Department of Electrical Engineering & Computer Science Information Technology & Telecommunications Research Center The University of Kansas jpgs@eecs.ku.edu http://www.ittc.ku.edu/~jpgs/courses/mwnets 19 November 2009 rev. 1.0 2004 2009 James P.G. Sterbenz Mobile Wireless Networking Wireless Sensor Networks SN.1 Sensor and actuator network overview SN.2 Sensor network architecture and topology SN.3 Sensor network hop-by-hop communication SN.4 Sensor network routing 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-2 1

Mobile Wireless Networking Sensor Network Introduction Wireless Sensor Networks specialised subset of mobile wireless networks currently a hot topic of research very few standards other than 802.15.4 and ZigBee enough material for an entire course! e.g. [KW2005] This EECS 882 lecture brief overview to the discipline emphasise differences from other mobile wireless nets and their implications to architecture and design 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-3 Wireless Sensor Networks SN.1 Sensor and Actuator Network Overview SN.1 Sensor and actuator network overview SN.2 Sensor network architecture and topology SN.3 Sensor network hop-by-hop communication SN.4 Sensor network routing 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-4 2

Sensor and Actuator Networks Motivation: Control Systems The world is full of control systems sensors provide inputs on the state of the system control algorithm processes parameters based on parameters actuators control the system control algorithm (processing) sensor actuator 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-5 Sensor and Actuator Networks Motivation: Distributed Control Systems The world is full of control systems sensors provide inputs on the state of the system control algorithm processes based on parameters actuators control the system Distributed control systems? parameters control algorithm (processing) sensor actuator 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-6 3

Sensor and Actuator Networks Motivation: Distributed Control Systems Distributed control systems need networks connecting elements sensor and actuator networks these are frequently wireless generally called WSNs wireless sensor networks actuators left out for brevity but sometimes WSANs parameters sensors control algorithm (processing) actuator 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-7 WSN Architecture Components Sensor device that senses information from environment Actuator device that controls environment Sink destination of sensor data for processing or storage Gateway interworking between WSN and data network typically the Internet note: no standard symbols for WSN components (IEC control systems symbols not really appropriate) 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-8 S 4

WSN Characteristics Introduction Defining characteristics of WSNs? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-9 WSN Characteristics Introduction Defining characteristics of WSNs wireless nodes energy efficiency critical difficult or impossible to replace battery large scale sensor fields may have thousand or millions of nodes ad hoc: manual configuration impractical frequently nodes have low duty cycle e.g. periodic temperature reports 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-10 5

WSN Characteristics Introduction Defining characteristics of WSNs wireless nodes energy efficiency critical large scale Important note: not all sensors/actuators are wireless nor energy constrained we will concentrate on those that are heterogeneous wired/wireless sensor networks have additional challenges SNs have additional interesting properties wired nodes can be exploited to assist wireless 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-11 Sensor Network Characteristics Differences from WPANs and MANETs WPAN: wireless personal network MANET: mobile ad hoc network Differences? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-12 6

Sensor Network Characteristics Differences from WPANs and MANETs Energy concerns WPAN and MANET nodes batteries generally rechargeable or replaceable WSN energy management more critical low duty cycle of sensors helps Limited mobility many sensors are stationary initial self-organisation more important dynamic reöptimisation less critical network must react to failed nodes that have no energy left 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-13 Sensor Network Characteristics Differences from SCADA Networks SCADA: supervisory control and data acquisition SCADA networks control industrial processes and utilities e.g. power grid, nuclear power plant, chemical plants Differences? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-14 7

Sensor Network Characteristics Differences from SCADA Networks SCADA: supervisory control and data acquisition SCADA networks control industrial processes and utilities e.g. power grid, nuclear power plant, chemical plants Links SCADA nodes traditionally wired within plant area energy not a concern wireless remote sensors/actuators becoming more common frequently for convenience rather than lack of power source Scale SCADA network scale generally thought of as smaller 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-15 Sensor Network Characteristics Differences from other Networks WSNs are generally data centric information important not necessarily related to particular nodes Examples average temperature of a region mapping of a storm or wildfire location of an animal Consequence? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-16 8

Sensor Network Characteristics In-Network Processing WSNs frequently manipulate data in the network sensor nodes not only relay multihop traffic but also process it on the way Why? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-17 Sensor Network Characteristics In-Network Processing WSNs frequently manipulate data in the network sensor nodes not only relay multihop traffic but also process it on the way More energy efficient processing generally cheaper then transmission e.g. nodes compute average, max, or min value significantly reduces communication cost referred to as sensor fusion 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-18 9

Sensor Network Characteristics In-Network Processing Types Aggregation compute statistical functions on the way to the sink average, min, max, etc. Edge detection compute and convey boundaries between values e.g isotherms, isobars, storm edges, wildfire boundaries Trajectory tracking e.g. animal movement Other variants possible 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-19 Wireless Sensor Networks Application Examples Environmental monitoring long term, e.g. climate change short term, e.g. wildfire mapping Medical and health vital signs and ongoing biochemical monitoring automated drug dosing Intelligent buildings fine-grained monitoring and control of temperature Military and homeland security situational awareness Many more! 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-20 10

Wireless Sensor Networks SN.2 Sensor Network Architecture & Topology SN.1 Sensor and actuator network overview SN.2 Sensor network architecture and topology SN.3 Sensor network hop-by-hop communication SN.4 Sensor network routing 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-21 Wireless Sensor Networks Alternative Architectures Single hop advantages and disadvantages? S 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-22 11

Wireless Sensor Networks Alternative Architectures Single hop simple architecture only appropriate for small WSNs distance and scale S 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-23 Wireless Sensor Networks Alternative Architectures Single hop simple architecture only appropriate for small WSNs distance and scale Multihop advantages and disadvantages? S 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-24 12

Wireless Sensor Networks Alternative Architectures Single hop simple architecture only appropriate for small WSNs distance and scale Multihop communication with limited transmission power may conserve energy but may not: energy use for transit traffic S 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-25 Wireless Sensor Networks Performance Metrics Conventional network metrics bandwidth, delay, etc. Energy-related metrics? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-26 13

Wireless Sensor Networks Performance Metrics Conventional network metrics bandwidth, delay, etc. Energy-related metrics energy/received-bit energy/event network lifetime: duration for network to remain operational time to first node failure half-life: time to 50% node failure time to partition etc. 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-27 Wireless Sensor Networks SN.3 Sensor Network HBH Communication SN.1 Sensor and actuator network overview SN.2 Sensor network architecture and topology SN.3 Sensor network hop-by-hop communication SN.3.1 Transceivers and physical communication SN.3.2 Medium access control SN.3.3 Inter-sensor link functions SN.3.4 802.15.4 low energy PAN and ZigBee SN.4 Sensor network routing 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-28 14

Wireless Sensor Networks Node Role Comparison network type node types IS role ES role transfer types traditional ES xor IS only transit no transit HBH vs. E2E MANET ES or IS (dual role) gateway transit HBH vs. E2E WSN ES (sensor) and sink sink data fusion HBH E2E 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-29 Wireless Sensor Networks Hop-by-Hop Communication Hop-by-hop communication in sensor networks physical layer communication links medium access control link layer functions 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-30 15

Wireless Sensor Networks Hop-by-Hop Communication Hop-by-hop communication in sensor networks physical layer communication links medium access control link layer functions Different from traditional network L1 L3 mechanisms optimised for? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-31 Wireless Sensor Networks Hop-by-Hop Communication Hop-by-hop communication in sensor networks physical layer communication links medium access control link layer functions Different from traditional network L1 L3 mechanisms optimised for: low energy lower data rates frequently acceptable not optimised for? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-32 16

Wireless Sensor Networks Hop-by-Hop Communication Hop-by-hop communication in sensor networks physical layer communication links medium access control link layer functions Different from traditional network L1 L3 mechanisms optimised for: low energy lower data rates frequently acceptable not optimised for: bandwidth (lower rates frequently acceptable) mobility (many sensors stationary once deployed) 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-33 Sensor Network HBH Communication SN.3.1 Transceivers & Physical Communication SN.1 Sensor and actuator network overview SN.2 Sensor network architecture and topology SN.3 Sensor network hop-by-hop communication SN.3.1 Transceivers and physical communication SN.3.2 Medium access control SN.3.3 Inter-sensor link functions SN.3.4 802.15.4 low energy WPAN and ZigBee SN.4 Sensor network routing 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-34 17

WSN HBH Communication Physical Layer Overview WSN physical layer issues similar to MANETs WPANs Coding goal generally not expensive coding for high bit rate goal generally is for efficient low energy transmission negligible spreading and multipath due to short range 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-35 WSN HBH Communication Transceiver Overview Transceivers use significant power transmission power transmit circuit power receiver circuit power How to manage? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-36 18

WSN HBH Communication Transceiver Overview Transceivers use significant power transmission power transmit circuit power receiver circuit power Power management: adaptive transmit power sleep when not transmitting sleep when not receiving problem? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-37 WSN HBH Communication Transceiver Overview Transceivers use significant power transmission power transmit circuit power receiver circuit power Power management: adaptive transmit power sleep when not transmitting sleep when not receiving need wakeup mechanism 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-38 19

Sensor Network HBH Communication SN.3.2 Medium Access Control SN.1 Sensor and actuator network overview SN.2 Sensor network architecture and topology SN.3 Sensor network hop-by-hop communication SN.3.1 Transceivers and physical communication SN.3.2 Medium access control SN.3.3 Inter-sensor link functions SN.3.4 802.15.4 low energy WPAN and ZigBee SN.4 Sensor network routing 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-39 WSN Medium Access Control Medium Access Control Issues WSN MAC: issues common with other wireless nets hidden and exposed nodes collisions in shared medium overhead and resource awareness What is different? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-40 20

WSN Medium Access Control Medium Access Control Issues WSN MAC: issues different from other wireless nets low duty cycle extreme energy management Problems? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-41 WSN Medium Access Control Medium Access Control Problems Sleeping receivers can t sense transmission schedule wakeups TDMA with synchronised clocks clustered, e.g. LEACH with rotating clusterheads S-MAC and T-MAC learn schedules from neighbours periodic wakeup with long preambles, e.g. B-MAC out-of-band wakeup 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-42 21

WSN Medium Access Control Medium Access Control Problems Low duty cycle increased need for wakeup mechanisms reduces the probability of collisions RTS/CTS not needed 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-43 Sensor Network HBH Communication SN.3.3 Inter-Sensor Links SN.1 Sensor and actuator network overview SN.2 Sensor network architecture and topology SN.3 Sensor network hop-by-hop communication SN.3.1 Transceivers and physical communication SN.3.2 Medium access control SN.3.3 Inter-sensor link functions SN.3.4 802.15.4 low energy WPAN and ZigBee SN.4 Sensor network routing 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-44 22

Link Layer Functions Link layer functions multiplexing framing error control flow control Concerns? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-45 Link Layer Concerns Link layer functions multiplexing framing error control flow control Wireless sensor network concerns energy conservation data-driven application reliability requirements 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-46 23

Multiplexing Link layer functions multiplexing framing error control flow control Wireless sensor network concerns energy conservation data-driven application reliability requirements 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-47 Multiplexing WSN multiplexing shared medium: handled by MAC algorithm 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-48 24

Framing Link layer functions multiplexing framing error control flow control Wireless sensor network concerns energy conservation data-driven application reliability requirements 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-49 Framing Link layer framing header and trailer encapsulation for HBH transmission link and MAC control information Issue? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-50 25

Framing Link layer framing header and trailer encapsulation for HBH transmission link and MAC control information Issue: overhead in-band: encapsulation overhead per frame out-of-band: MAC overhead per frame Choice: frame size 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-51 Framing: Small Frames Small frames higher header overhead: more xmit energy consumed lower packet error rate / BER lower ARQ energy isolates effects of independent bit errors to smaller chunks 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-52 26

Framing: Large Frames Small frames higher header overhead: more xmit energy consumed lower packet error rate / BER less ARQ energy consumed isolates effects of independent bit errors to smaller chunks Large frames lower header overhead less energy consumed higher packet error rate / BER more ARQ energy may be ameliorated by hybrid ARQ+FEC 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-53 Framing: Frame Size Tradeoff Optimal frame size is f (E b, BER) bit energy = E b Cross-layer optimisation dynamically adjust frame size based on BER and E b 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-54 27

Error Control Link layer functions multiplexing framing error control flow control Wireless sensor network concerns energy conservation data-driven application reliability requirements 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-55 Error Control Options Error control options ARQ FEC hybrid none Tradeoffs? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-56 28

Error Control Options Error control options: ARQ when to use? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-57 Error Control Options: ARQ Error control options: ARQ required for reliable HBH transfer why? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-58 29

Error Control Options: ARQ ARQ reliability issues required for reliable HBH transfer may be needed for in-network processing not needed for reliable E2E transfer may enhance performance 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-59 Error Control Options: ARQ ARQ reliability issues required for reliable HBH transfer may be needed for in-network processing not needed for reliable E2E transfer may enhance performance ARQ energy issues may reduce energy relative to only E2E ARQ why? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-60 30

Error Control Options: ARQ ARQ reliability issues required for reliable HBH transfer may be needed for in-network processing not needed for reliable E2E transfer may enhance performance ARQ energy issues may reduce energy relative to only E2E ARQ cost of single HBH retransmission < cost of multiple hops cost only incurred on bit error implication? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-61 Error Control Options: ARQ ARQ reliability issues required for reliable HBH transfer may be needed for in-network processing not needed for reliable E2E transfer may enhance performance ARQ energy issues may reduce energy relative to only E2E ARQ cost of single HBH retransmission < cost of multiple hops cost only incurred on bit error better when Pr[error] low 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-62 31

Error Control Options: FEC Reliability FEC reliability issues sufficient for quasi-reliable HBH transfer may enhance E2E performance why? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-63 Error Control Options: FEC Reliability FEC reliability issues sufficient for quasi-reliable HBH transfer may enhance E2E performance reduces the Pr[E2E retransmission] 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-64 32

Error Control Options: FEC Energy FEC Energy issues may save energy vs. E2E only ARQ why? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-65 Error Control Options: FEC Energy FEC Energy issues may save energy vs. E2E only ARQ reduces Pr[E2E retransmission] more flexible then E2E FEC why? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-66 33

Error Control Options: FEC Energy FEC Energy issues may save energy vs. E2E only ARQ reduces Pr[E2E retransmission] more flexible then E2E FEC appropriate strength can be applied to each link energy costs of coding must be considered per node what BER range to use? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-67 Error Control Options: FEC Energy FEC Energy issues may save energy vs. E2E only ARQ reduces Pr[E2E retransmission] more flexible then E2E FEC appropriate strength can be applied to each link energy costs of coding must be considered per node more attractive when Pr[error] high coding/decoding cost incurred whether or not bit error block code more energy efficient than convolutional codes 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-68 34

Error Control Options: Hybrid Hybrid error control reliability issues combine FEC and ARQ to optimise HBH & E2E performance Hybrid error control energy issues globally optimise energy consumption 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-69 Error Control Options: No Error Control Unreliable error control many sensor applications do not need reliable transfer e.g. periodic monitoring: average or interpolate missing points Unreliable error control energy issues don t use energy on unneeded error control 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-70 35

Error Control Flexibility Error control options context dependent: channel characteristics network dependent: topology and network diameter application dependent: reliability model Cross-layer optimisations knobs: application to specify error requirements to link layer dials: channel characteristics instrumented to link layer proper mechanism and parameter choices can be made 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-71 Sensor Network HBH Communication SN.3.4 802.15.4 Low Energy WPAN SN.1 Sensor and actuator network overview SN.2 Sensor network architecture and topology SN.3 Sensor network hop-by-hop communication SN.3.1 Transceivers and physical communication SN.3.2 Medium access control SN.3.3 Inter-sensor link functions SN.3.4 802.15.4 low energy WPAN and ZigBee SN.4 Sensor network routing SN.5 Sensor network end-to-end transport 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-72 36

IEEE 802 Networks 802.15.4 Relation to other 802 Protocols 802.16 WMAN 802.11 WLAN WPAN 802.15 IEEE 802.15.4 part of 2nd generation wireless protocols (802.15 & 802.16) no similarity to 802.11/Ethernet framing or operation no similarity to other 802.15 protocols 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-73 802.15.4 Low Energy WPAN WPAN Overview WPAN: Wireless Personal Area Networks IEEE 802.15 grouper.ieee.org/groups/802/15 Short-reach wireless network shorter range than 802.11 lower energy than 802.15.1 (and 802.15.3) officially Low Rate WPANs Applications [www.ieee802.org/15/pub/tg4.html] sensors interactive toys smart badges remote controls home automation 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-74 37

802.15.4 LR-WPAN Physical Layer Characteristics 900 MHz and 2.4 GHz unlicensed ISM band implications? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-75 802.15.4 LR-WPAN Physical Layer Characteristics 2.4 GHz unlicensed ISM band most of world interference issues: 802.11b/g, 802.1 and cordless phones 250 kb/s in 16 channels DSSS 915 MHz unlicensed ISM band North America, Australia, New Zealand, some of S. America 40 250 kb/s in 10 channels DSSS or PSSS 868 MHz unlicensed band Europe 20 250 kb/s in 1 channel; plans to expand to 4 channels DSSS or PSSS (parallel sequence SS: ASK+FSK) 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-76 38

802.15.4 LR-WPAN Medium Access Control: Node Roles Device node in an 802.15.4 network identified by 64-bit IEEE EUI-64 address Coördinator manages devices in 802.15.4 network assigns 16-bit short addresses for use in network beacons 16-bit PAN identifier beacons list of outstanding frames for devices exchanges data with devices in network exchanges data with peer coordinators cluster-tree topology 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-77 802.15.4 LR-WPAN Medium Access Control Superframe 802.15.4 superframe active period (16 slots) beacon (1 slot) CAP: contention access period for CSMA GTS: guaranteed time slots (GTS) for TDMA devices request and are allocated GTSs from coördinator permits QoS 802.15.4 superframe inactive period variable length time during which nodes sleep active period inactive period beacon CAP GTS 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-78 39

802.15.4 LR-WPAN Medium Access Control Data exchange beacon REQ ACK data ACK 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-79 7 ZigBee Overview ZigBee protocol specification upper level protocols for WSNs uses 802.15.4 MAC and PHY ZigBee Alliance industry consortium that maintains standard similar to Bluetooth, but not a L1 7 stovepipe 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-80 40

ZigBee Protocol Architecture ZigBee IEEE 802.15.4 [ZigBee spec] 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-81 ZigBee Protocols Routing management AODV and neurfon 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-82 41

Sensor Network HBH Communication SN.4 Sensor Network Routing SN.1 Sensor and actuator network overview SN.2 Sensor network architecture and topology SN.3 Sensor network hop-by-hop communication SN.4 Sensor network routing SN.4.1 Sensor identifiers and addressing SN.4.2 Sensor network routing algorithms 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-83 Sensor Network HBH Communication SN.4.1 Sensor Identifiers and Addressing SN.1 Sensor and actuator network overview SN.2 Sensor network architecture and topology SN.3 Sensor network hop-by-hop communication SN.4 Sensor network routing SN.4.1 Sensor identifiers and addressing SN.4.2 Sensor network routing algorithms 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-84 42

Identifiers and Addressing Introduction and Terminology Identifier : string used to identify an object e.g. sensor network node 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-85 Identifiers and Addressing Introduction and Terminology Identifier : string used to identify an object e.g. sensor network node Name : globally-unique persistent identifier [RFC 1737] e.g. James Philip Guenther Sterbenz note a DNS identifier is not really a name neither unique nor persistent for a given entity 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-86 43

Identifiers and Addressing Introduction and Terminology Identifier : string used to identify an object e.g. sensor network node Name : globally-unique persistent identifier [RFC 1737] e.g. James Philip Guenther Sterbenz note a DNS identifier is not really a name neither unique nor persistent for a given entity Address : location of a object within a topology may be topological physical, e.g. A.3.14 logical, e.g. 129.237.125.27 may be geographic, e.g. 38.957 N 95.254 W 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-87 Identifiers and Addressing Introduction and Terminology Identifier : string used to identify an object Name : globally-unique persistent identifier [RFC 1737] Address : location of a object within a topology Problem: the networking community is very sloppy in this terminology e.g. DNS name e.g. IEEE MAC address but arguably a random address in a flat topology 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-88 44

Identifiers and Addressing Issues and Concerns for WSNs Issues and concerns for WSNs? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-89 Sensor Network HBH Communication SN.4.2 Sensor Network Routing SN.1 Sensor and actuator network overview SN.2 Sensor network architecture and topology SN.3 Sensor network hop-by-hop communication SN.4 Sensor network routing SN.4.1 Sensor identifiers and addressing SN.4.2 Sensor network routing algorithms 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-90 45

Sensor Network Routing Challenges Challenges [KK2004] node deployment: random, multihop relaying needed 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-91 Sensor Network Routing Overview and Issues Classification [ASSC 2002], [KK2004] data-centric flat data-centric hierarchical location-based 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-92 46

Sensor Network Routing Data-Centric Routing Flat data-centric routing (selected variants) flooding gossiping directed diffusion SPIN rumour-based 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-93 Sensor Network Routing Flooding Flooding analogy: shouting to everyone advantages and disadvantages? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-94 47

Sensor Network Routing Flooding: Advantages Flooding advantages + simple: less processing energy savings 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-95 Sensor Network Routing Flooding: Disadvantages Flooding advantages + simple: less processing energy savings Flooding disadvantages implosion: overhead of duplicate messages overlap: multiple nodes report identical information resource blindness: no consideration for energy constraints energy waste generally energy (CPU) < energy (transmission) So what? any differences from problems in MANETs? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-96 48

Sensor Network Routing Flooding Tradeoffs Flooding advantages + simple: less processing energy savings Flooding disadvantages implosion, overlap, resource blindness energy waste Tradeoffs energy use even more of a concern than MANET Alternative to flooding that exploits both advantages? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-97 Sensor Network Routing Gossiping Gossiping : restricted form of flooding send only to fraction of neighbours analogy: whispering to a friend, who does the same, advantages and disadvantages? 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-98 49

Sensor Network Routing Gossiping: Advantages Gossiping : restricted form of flooding sent only to fraction of neighbours Gossiping advantages + still relatively simple + energy savings fraction of neighbors 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-99 Sensor Network Routing Gossiping: Advantages Gossiping : restricted form of flooding sent only to fraction of neighbours Gossiping advantages + still relatively simple + energy savings fraction of neighbors Gossiping disadvantages probability of delivery related to fraction of neighbours 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-100 50

Sensor Network Routing SPIN SPIN sensor protocols for information via negotiation data-centric routing based on metadata Source of data advertises data ADV message is broadcast to neighbours Interested neighbours request data typically neighbours that do not already have data REQ message returned Source of data replies DATA message contains data 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-101 Sensor Network Routing Directed Diffusion Directed diffusion data-centric routing based on attribute-value pairs Sink of data expresses interest in type of data interest is propagated (flooded) through the network node cache interests Nodes establish gradients for data gradient = (direction, strength) to neighbours optimises path of data delivery Events are delivered along gradients to sink node perform data fusion 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-102 51

Wireless Sensor Networks Further Reading Holger Karl and Andreas Willig, Protocols and Architectures for Wireless Sensor Networks, Wiley, 2005 I.F. Akyildiz, W. Su, Y Sankarasubramaniam, and E. Cayirci Wireless Sensor Networks: A Survey Computer Networks, vol.38 iss. 4, Mar. 2002, pp. 393 422 Kemal Akkaya and Mohamed Younis, A Survey on Routing Protocols for Wireless Sensor Networks Ad Hoc Networks, vol.3 iss. 3, May 2005, pp. 325 349 Jamal N. Al-Karaki and Ahmed E. Kamal, Routing Techniques in Wireless Sensor Networks: A Survey IEEE Wireless Communications, Dec. 2004, pp. 6 28 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-103 Wireless Sensor Networks Acknowledgements Some material in these foils is based on the textbook Murthy and Manoj, Ad Hoc Wireless Networks: Architectures and Protocols Some material in these foils enhanced from EECS 780 foils 19 November 2009 KU EECS 882 Mobile Wireless Nets Sensor Networks MWN-MT-104 52