ITTC Mobile Wireless Networking

© James P.G. SterbenzITTCMobile Wireless NetworkingThe University of Kansas EECS 882

Wireless Sensor Networks

© 2004–2011 James P.G. Sterbenz28 November 2011

James P.G. Sterbenz

Department of Electrical Engineering & Computer ScienceInformation Technology & Telecommunications Research Center

The University of Kansas

[email protected]

http://www.ittc.ku.edu/~jpgs/courses/mwnets

rev. 11.0

28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-2

© James P.G. SterbenzITTC

Mobile Wireless NetworkingWireless Sensor Networks

SN.1 Sensor and actuator network overviewSN.2 Sensor network architecture and topologySN.3 Sensor network hop-by-hop communicationSN.4 Sensor network routing



Mobile Wireless NetworkingSensor Network Introduction

• Wireless Sensor Networks– specialised subset of mobile wireless networks– still a fairly 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– introduction to 802.15.4 and ZigBee standards



Wireless Sensor NetworksSN.1 Sensor and Actuator Network Overview




Sensor and Actuator NetworksMotivation: 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 systemcontrol

algorithm(processing)

sensor

actuator

parameters



Sensor and Actuator NetworksMotivation: 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? controlalgorithm

(processing)

sensor

actuator

parameters



Sensor and Actuator NetworksMotivation: 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

actuatorcontrolalgorithm

(processing)

parameters sensors



WSN ArchitectureComponents

• 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)

S



WSN CharacteristicsIntroduction

Defining characteristics of WSNs?




• 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




• 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



Sensor Network CharacteristicsDifferences from WPANs and MANETs

• WPAN: wireless personal network• MANET: mobile ad hoc network

Differences?




• WPAN: wireless personal network• MANET: mobile ad hoc network

Energy concerns?




• Energy concerns– WPAN and MANET nodes batteries

• generally rechargeable or replaceable

– WSN energy management more critical• batteries generally assumed not replicable• low duty cycle of sensors helps

Mobility aspects?




• Energy concerns– WPAN and MANET nodes batteries

• generally rechargeable or replaceable

– WSN energy management more critical• batteries generally assumed not replicable• 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



Sensor Network CharacteristicsDifferences 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?



Sensor Network CharacteristicsDifferences 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



Sensor Network CharacteristicsDifferences 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?



Sensor Network CharacteristicsIn-Network Processing

• WSNs frequently manipulate data in the network– sensor nodes not only relay multihop traffic…– but also process it on the way

Why?



Sensor Network CharacteristicsIn-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 Lecture EM– e.g. nodes compute average, max, or min value

• significantly reduces communication cost

– referred to as sensor fusion or data fusion



Sensor Network CharacteristicsIn-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…



Wireless Sensor NetworksApplication 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!



Wireless Sensor NetworksSN.2 Sensor Network Architecture & Topology




Wireless Sensor NetworksAlternative Architectures

• Single hopadvantages and disadvantages?

S




• Single hop– simple architecture– only appropriate for small WSNs

• distance and scaleS





• distance and scale

• Multihopadvantages and disadvantages?

S





• distance and scale

• Multihop– communication with

limited transmission power– may conserve energy

• but may not:energy use for transit traffic

S



Wireless Sensor NetworksPerformance Metrics

• Conventional network metrics– bandwidth, delay, etc.

Energy-related metrics?



Wireless Sensor NetworksPerformance 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.



Wireless Sensor NetworksSN.3 Sensor Network HBH Communication

SN.1 Sensor and actuator network overviewSN.2 Sensor network architecture and topologySN.3 Sensor network hop-by-hop communication

SN.3.1 Transceivers and physical communicationSN.3.2 Medium access controlSN.3.3 Inter-sensor link functionsSN.3.4 802.15.4 low energy PAN and ZigBee

SN.4 Sensor network routing



Wireless Sensor NetworksNode Role Comparison

network type node types IS role ES role transfer types

traditional ES xor IS only transit

no transit

transit

data fusion

HBH vs. E2E

MANET ES or IS (dual role)

gateway HBH vs. E2E

WSN ES (sensor) and sink

sink HBH ≈ E2E



Wireless Sensor NetworksHop-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 mechanismsoptimised for?





• Different from traditional network L1–L3 mechanisms– optimised for:

• low energy• lower data rates frequently acceptable

not optimised for?





• 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)



Sensor Network HBH CommunicationSN.3.1 Transceivers & Physical Communication


SN.3.1 Transceivers and physical communicationSN.3.2 Medium access controlSN.3.3 Inter-sensor link functionsSN.3.4 802.15.4 low energy WPAN and ZigBee




WSN HBH CommunicationPhysical 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



WSN HBH CommunicationTransceiver Overview

• Transceivers use significant power– transmission power– transmit circuit power– receiver circuit power

How to manage?





• Power management: Lecture EM– adaptive transmit power– sleep when not transmitting– sleep when not receiving

problem?





• Power management:– adaptive transmit power– sleep when not transmitting– sleep when not receiving

• need wakeup mechanism• may be OK to miss reception of some items of similar data



Sensor Network HBH CommunicationSN.3.2 Medium Access Control






WSN Medium Access ControlMedium 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?



WSN Medium Access ControlMedium Access Control Issues

• WSN MAC: issues different from other wireless nets– low duty cycle– extreme energy management

Problems?



WSN Medium Access ControlMedium 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



WSN Medium Access ControlMedium Access Control Problems

• Low duty cycle– increased need for wakeup mechanisms– reduces the probability of collisions

• RTS/CTS not needed



Sensor Network HBH CommunicationSN.3.3 Inter-Sensor Links






WSN Link ProtocolsLink Layer Functions

• Link layer functions– multiplexing– framing– error control– flow control

Concerns?



WSN Link ProtocolsLink Layer Concerns


• Wireless sensor network concerns– energy conservation– data-driven application reliability requirements



WSN Link ProtocolsMultiplexing





WSN Link ProtocolsMultiplexing

• WSN multiplexing– shared medium: handled by MAC algorithm



WSN Link ProtocolsFraming






• Link layer framing– header and trailer encapsulation for HBH transmission– link and MAC control information

Issue?




• 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



WSN Link ProtocolsFraming: 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



WSN Link ProtocolsFraming: 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



WSN Link ProtocolsFraming: Frame Size Tradeoff

• Optimal frame size is f (Eb, BER)– bit energy = Eb

• Cross-layer optimisation– dynamically adjust frame size based on BER and Eb



WSN Link ProtocolsError Control





WSN Link ProtocolsError Control Options

• Error control options– ARQ– FEC– hybrid– none

Tradeoffs?



WSN Link ProtocolsError Control Options

• Error control options: ARQ– when to use?



WSN Link ProtocolsError Control Options: ARQ

• Error control options: ARQ– required for reliable HBH transfer

why?




• 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?






• ARQ energy issues– may reduce energy relative to E2E-only ARQ

• cost of single HBH retransmission < cost of multiple hops

– cost only incurred on bit errorimplication?






• 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



WSN Link ProtocolsError Control Options: FEC Reliability

• FEC reliability issues– sufficient for quasi-reliable HBH transfer– may enhance E2E performance

why?



WSN Link ProtocolsError Control Options: FEC Reliability

• FEC reliability issues– sufficient for quasi-reliable HBH transfer– may enhance E2E performance

• reduces the Pr[E2E retransmission]



WSN Link ProtocolsError Control Options: FEC Energy

• FEC Energy issues– may save energy vs. E2E only ARQ

why?





• reduces Pr[E2E retransmission]

– more flexible then E2E FECwhy?






– 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?






– 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



WSN Link ProtocolsError 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



WSN Link ProtocolsError 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



WSN Link ProtocolsError Control Flexibility

• Error control options– context dependent: channel characteristics– network dependent: topology and network diameter– application dependent: reliability model

• Cross-layer optimisations Lecture XL– knobs: application to specify error requirements to link layer– dials: channel characteristics instrumented to link layer– proper mechanism and parameter choices can be made



Sensor Network HBH CommunicationSN.3.4 802.15.4 Low Energy WPAN



SN.4 Sensor network routingSN.5 Sensor network end-to-end transport



IEEE 802 Networks802.15.4 Relation to other 802 Protocols

802.11 WLAN

WPAN802.15

802.16 WMAN

• 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



802.15.4 Low Energy WPANWPAN Overview

• WPAN: Wireless Personal Area Networks– IEEE 802.15 grouper.ieee.org/groups/802/15

• 802.15.4 short-reach wireless network– shorter range than 802.11 WLANs and 802.16 WMANs– 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



802.15.4 Low Energy WPANStandards Overview

Standard Year Freq

2003 868/915 MHz2.4 GHz

780 MHz

950 MHz

2007

2006

2009

2009

Rates Note

802.15.4-2003 20, 40 Kb/s250 kb/s

original standard

802.15.4a additional PHY

802.15.4b enhancements

802.15.4-2006 15.4-2003+15.4b

802.15.4c 250 kb/s China

802.15.4d 20, 100 kb/s Japan



802.15.4 LR-WPANPhysical Layer Characteristics

• 900 MHz and 2.4 GHz unlicensed ISM bandimplications?




• 2.4 GHz unlicensed ISM band– most of world– interference issues: 802.11b/g, 802.15, 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)



802.15.4 LR-WPANPhysical Layer Tradeoffs

• 900 MHz and 2.4 GHz unlicensed ISM bandtradeoffs?



802.15.4 LR-WPANPhysical Layer Tradeoffs

• 915 and 868 MHz unlicensed bands– lower data rates (with simple coding)+ lower power+ longer range+ fewer interference sources

• 2.4 GHz unlicensed ISM band+ higher data rates– higher power– shorter range– more interference sources




Spreading Parameters Data Parameters

Chip Rate[kchip/s]

Modulation Rate[kb/s]

Rate[ksym/s]

Symbols

868.0 – 868.6 300 BPSK 20 20 binary

902 – 928 600 BPSK 40 40 binary

868.0 – 868.6 400 ASK 250 12.5 20b PSSS

902 – 928 1600 ASK 250 50 5b PSSS

868.0 – 868.6 400 O-QPSK 100 25 16ary orth

902 – 928 1000 O-QPSK 250 62.5 16ary orth

2450 2044 – 2483.5 2000 O-QPSK 250 62.5 16ary orth

868/915optional

868/915optional

868/915

PHY Freq. Band[MHz]



802.15.4 LR-WPANPhysical Layer Characteristics (15.4a UWB)


Chip Rate[kchip/s]


Rate[ksym/s]

Symbols

UWBsub-GHz 250–750

UWBlow 3244–4742

UWBhigh 5944–10234

245CSS 2044 – 2483.5 250

1000 166.667

PHY Freq. Band[MHz]



802.15.4 LR-WPANPhysical Layer Characteristics (15.4c/d CJ)


Chip Rate[kchip/s]


Rate[ksym/s]

Symbols

779–787 1000 O-QPSK 250 62.5 16ary orth

779–787 1000 MPSK 250 62.5 16ary orth

950–956 300 BPSK 20 20 binary

950–956 – GFSK 100 100 binary

2450 2044 – 2483.5 2000 O-QPSK 250 62.5 16ary orth

950Japan

780China

PHY Freq. Band[MHz]



802.15.4 LR-WPANChannel Numbering

• 32 bit channel identifier• 32 pages

– 5-MSB binary encoding of pages– pages 0, 1, 2 currently defined; 3 – 31 reserved for future

• 27 channels/page– 27-LSB bit-vector of channels– multiple channels may be used by node



802.15.4 LR-WPANChannel Numbering

Page Channel Description

0 826 MHz BPSK

1 – 10 915 MHz BPSK

11 – 26 2.4 GHz O-QPSK

0 868 MHz ASK

1 – 10 915 MHz ASK

11 – 26 reserved

0 868 MHz O-QPSK

1 – 10 915 MHZ O-QPSK

11 – 26 reserved

3 – 31 reserved reserved

2

1

0



802.15.4 LR-WPANPhysical Layer Responsibilities

• 802.15.4 physical layer [802.15.4-2006 §6.1]– transceiver activation and deactivations– ED: energy detection within current channel– LQI: link quality indicator for received packets– CCA: clear channel assessment for CSMA/CA– channel frequency selections– data transmission and reception



802.15.4 LR-WPANChannel Modulation: O-QPSK

• O-QPSK: quasi-orthogonal QPSK– each data octet split into two 4-bit symbols– symbols mapped to 16 nearly-orthogonal 32-b chip values– symbols alt. modulated to in-phase and quadrature carriers

• I-phase: even-indexed symbols• Q-phase: odd-indexed symbols time-shifted by ½ symbol time

• BPSK• ASK



802.15.4 LR-WPANChannel Modulation: B-PSK

• O-QPSK• BPSK: binary phase-shift keying

– differential encoding (xor with previous bit)– DSSS with 15-bit chip value

• 1 = 111101011001000• 0 = 000010100110111

• ASK



802.15.4 LR-WPANChannel Modulation: ASK PSSS

• O-QPSK• BPSK• ASK: amplitude shift keying

– PSSS: parallel-sequence spread spectrum• type of OCDM: orthogonal code division multiplexing

– each bit multiplied by 32 +/–1 chip sequence– bits grouped into to symbols

• 5 b/sym for 915 MHz, 20 b/sym for 868 MHz

– bit group added chip-wise to get 32-chip multilevel symbol– result ASK enocded



802.15.4 LR-WPANMedium Access Control: Devices

• Device– node in an 802.15.4 network– identified by 64-bit IEEE EUI-64 address– may be assigned 16-bit short address

• Device types– FFD: full-function device can serve as coördiantor or device– RFD: reduced-function devices can only communicate FFDs



802.15.4 LR-WPANMedium Access Control: Coördinator

• Coördinator– may be powered; sink in generic terminology– manages devices in 802.15.4 PAN– 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



802.15.4 LR-WPANMedium Access Control: PAN Topologies

C

FFD

RFD

based on [802.15.4-2006]

FFD

RFD

RFD

RFD

C

FFD

FFDRFD

FFD

star topology peer-to-peer topology



802.15.4 LR-WPANMedium Access Control: Star Topology

C

FFD

RFD

FFD

RFD

RFD

RFD

star topology • Star topology formation– FFD decides to be controller– chooses unique PAN ID

• within radio range

– other FFDs and RFDs join PAN



802.15.4 LR-WPANMedium Access Control: P2P Topologies

based on [802.15.4-2006]

C

FFD

FFDRFD

FFD

peer-to-peer topology• P2P topology formation– FFD controller election

• e.g. first active

• other nodes associate



802.15.4 LR-WPANMedium Access Control: Cluster Tree Network

C

RFD

RFD

RFD

RFD

RFD

PAN ID 0

RFDRFD

C

FFD

RFD

RFD

C

RFDRFD

RFDRFD

C

FFDRFD

FFDFFD

FFD

PAN ID 2PAN ID 1

PAN ID 0



802.15.4 LR-WPANMedium 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

beacon

inactive period

CAP GTS



PSDU

0 – 127 B

802.15.4 LR-WPANPHY Protocol Data Unit (PPDU) Format

PHY5.375–8.5B

MHRMAC header

FCS

• SHR (sync hdr) [4.375–7.5B]– preamble = 0 [3.75–5B]– SFD [5b–2.5B]

start frame delimiter= 11100101 (O-QPSK and BPSK)= inverted 0 symbol (ASK)

• PHR (PHY header) [1B]– frame length [7b]– reserved [1b]

• PSDU (PHY SDU) [0–127B]– PHY payload

• includes MAC hdr [3–23B]• includes FCS [2B]

note: length ranges depend on PHY

00000000 00000000

00000000 11100101

preamble + SFD

length PHR

PSDUMACframe

0–127B



802.15.4 LR-WPANFrame Format (PSDU)

2B

MAC header3–23B

seq#

dest. PAN ID

FCS

frame body

0 – 127 B

• MAC Header [3–23B]– frame control [2B]– sequence no. [1B]– dest. PAN ID [0|2B]– dest. address [0|2|8B]– source PAN ID [0|2B]– source address [0|2|8B]– aux sec hdr [0|5|6|10|14B]

• Frame body [0–2312B]

• MFR (MAC footer) Trailer: FCS [2B]

dest. address

soruce PAN ID

source address

aux. security hdr

controlframe



802.15.4 LR-WPANFrame Format: Frame Control

2B

MAC header3–23B

seq#

dest. PAN ID

FCS

frame body

0 – 127 B

• MAC Header [3–23B]– frame control [2B]

– frame type [3b]– sec. enabled [1b]– frame pending [1b]– ack request [1b]– PANID compress [1b]– reserved [3b]– dest addr mode [2b]– frame version [2b]– src addr mode [2b]

– sequence no. [1B]

dest. address

soruce PAN ID

source address

aux. security hdr

controlframe



802.15.4 LR-WPANFrame Format: Addressing Fields

2B

MAC header3–23B

seq#

dest. PAN ID

FCS

frame body

0 – 127 B

• MAC Header [3–23B]– dest. PAN ID [0|2B]– dest. address [0|2|8B]– source PAN ID [0|2B]– source address [0|2|8B]

• Address consists of tuple– PAN ID, node address– src PANID,addr present if FC samode≠00

dest. address

soruce PAN ID

source address

aux. security hdr

controlframe



802.15.4 LR-WPANFrame Format: Addresses

• Address– 64-bit IEEE EUI-64 for scalability

or– 16-bit short address for efficiency



802.15.4 LR-WPANFrame Types

• Frame types– 000 beacon frame– 001 data frame– 010 acknowledgement frame– 011 MAC command frame



802.15.4 LR-WPANCommand Frame Types

• Command frame types– 0001 association request– 0010 association response– 0011 disassociation notification– 0100 data request– 0101 PAN ID conflict notification– 0110 orphan notification– 0111 beacon request– 1000 coördinator realignment– 1001 GTS (guaranteed time slot) request



802.15.4 LR-WPANMedium Access Control

• Data exchange

7

beacon

REQ

data

ACK

ACK



ZigBeeOverview

• 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



ZigBeeProtocol Architecture

IEEE 802.15.4

ZigBee

[ZigBee spec]



ZigBeeProtocols

• Routing management– AODV and neuRFon



Sensor Network HBH CommunicationSN.4 Sensor Network Routing


SN.4.1 Sensor identifiers and addressingSN.4.2 Sensor network routing algorithms



Sensor Network HBH CommunicationSN.4.1 Sensor Identifiers and Addressing





Identifiers and AddressingIntroduction 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





• 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




• 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



Identifiers and AddressingIssues and Concerns for WSNs

Issues and concerns for WSNs?



Sensor Network HBH CommunicationSN.4.2 Sensor Network Routing





Sensor Network RoutingChallenges

• Challenges [KK2004]– node deployment: random, multihop relaying needed



Sensor Network RoutingOverview and Issues

• Classification [ASSC 2002], [KK2004]– data-centric flat– data-centric hierarchical– location-based



Sensor Network RoutingData-Centric Routing

• Flat data-centric routing (selected variants)– flooding– gossiping– directed diffusion– SPIN– rumour-based



Sensor Network RoutingFlooding

• Flooding– analogy: shouting to everyone

advantages and disadvantages?



Sensor Network RoutingFlooding: Advantages

• Flooding advantages+ simple: less processing → energy savings



Sensor Network RoutingFlooding: Disadvantages


• 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?



Sensor Network RoutingFlooding Tradeoffs


• 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?



Sensor Network RoutingGossiping

• Gossiping : restricted form of flooding– send only to fraction of neighbours– analogy: whispering to a friend, who does the same, …

advantages and disadvantages?



Sensor Network RoutingGossiping: Advantages

• Gossiping : restricted form of flooding– sent only to fraction of neighbours

• Gossiping advantages+ still relatively simple+ energy savings ∝ fraction of neighbors



Sensor Network RoutingGossiping: 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



Sensor Network RoutingSPIN

• 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



Sensor Network RoutingDirected 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



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 SurveyIEEE Wireless Communications, Dec. 2004, pp. 6–28



Wireless Sensor NetworksAcknowledgements

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

ITTC Mobile Wireless Networking

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Transcript of ITTC Mobile Wireless Networking