Wireless Sensor Networks: a Survey on the State of the Art and the 802.15.4 and ZigBee Standards

1
Wireless Sensor Networks a Survey on the State
of the Artand the 802.15.4 and ZigBee Standards

• Final Presentation
• 5 August 2008
• Omer Alkhnbashi

2
Content

• ZigBee and IEEE802.15.4 Overview
• IEEE 802.15.4 PHY.
• IEEE 802.15.4 MAC.
• ZigBee Functional Layers Architecture Protocol
  Stack.
• Security.
• Routing.
• Energy Efficiency.
• Localization.

3
Introduction

• 802.15.4 standard defines the characteristics of
• the physical and MAC
  layers for LR WPANs.
• ZigBee builds upon the IEEE 802.15.4 standard
  and
• defines the network layer
  specifications and
• provides a framework for
  application programming
• in the application layer.

Motorola www.motorola.com/zigbee
4
ZigBee Responsibilities

• Designed for wireless controls and sensors
• Operates in Personal Area Networks (PANs) and
  device-to-device networks
• Connectivity between small packet devices
• Control of lights, switches, thermostats,
  appliances, etc.

5
Why do we need ZigBeetechnology?

• No standard approach today that addresses the
  unique
• needs of most remote monitoring and control
  applications
• Enables the broad-based deployment of reliable
  wireless networks with low-complexity, low-cost
  solutions.
• Provides the ability to run for years on
  inexpensive primary batteries for a typical
  monitoring application.
• Capable of inexpensively supporting robust mesh
  networking technologies.

6
IEEE 802.15.4 PHY Operating Frequency Bands

• Direct Sequence Spread Spectrum (DSSS)
• Channel switching, link quality estimation,
  energy detection measurement and clear channel
  assessment to assist the channel selection

ZigBee Alliance Homepage
7
IEEE 802.15.4 PHY Packet Structure

• PHY Packet Fields
• - Preamble (32 bits) synchronization
• - Start of Packet Delimiter (8 bits) -
  specifies one of 3 packet types
• - PHY Header (8 bits) PSDU length, Sync
  Burst flag
• - PSDU (0 to 127 bytes) Data field

Start of Packet Delimiter
PHY Header
PHY Service Data Unit (PSDU)
Preamble
6 Bytes
0-127 Bytes
ZigBee Alliance Homepage
8
IEEE 802.15.4 MACDevice Classes

• Full function device (FFD)
• Any topology
• Network coordinator capable
• Talks to any other device
• Reduced function device (RFD)
• Limited to star topology
• Cannot become a network coordinator
• Talks only to a network coordinator
• Very simple implementation

9
IEEE 802.15.4 MAC modes of operation

• Non-beacon mode
• 802.15.4 makes use of CSMA-CA (carrier sense
  multiple access with collision avoidance)
• A clear channel assessment (CCA) is carried out
  before sending on the radio channel.
• If the channel is NOT clear, we wait for a random
  period of time, before trying to retransmit.
• Beacon mode
• Beacon mode introduces the superframe structure
  to divide time into different transmission
  periods (Beacon, CAP, CFP and inactive)
• During the CAP (Contention Access Period)
  communication is carried out like in non-beacon
  mode. CCAs are aligned with the
  transmission/reception of the beacon.

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IEEE 802.15.4 MAC Frame Structure

• A beacon frame - used by a coordinator to
  transmit beacons.
• A data frame - used for all transfers of data.
• An acknowledgment frame - used for confirming
  successful frame reception.
• A MAC command frame - used for handling all MAC
  peer entity control transfers.

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IEEE 802.15.4 MAC Super-frame
Guarantee Time Slot
Contention Access period
12
IEEE 802.15.4 MAC Super-frame
13
IEEE 802.15.4 MAC Super-frame
Data for node B
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IEEE 802.15.4 MAC Super-frame
Ack
Store message
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IEEE 802.15.4 MAC Super-frame
bacon Data pending For B
16
IEEE 802.15.4 MAC Super-frame
Data request
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IEEE 802.15.4 MAC Super-frame
Data reply
Beacon
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ZigBee Functional Layers Architecture Protocol
Stack
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Network Layer Functions

• Starting a network Able to establish a new
  network.
• Joining and Leaving Network Nodes are able to
  become members of the network as well as quit
  being members.
• Configuration Ability of the node to configure
  its stack to operate in accordance with the
  network type.
• Addressing The ability of a ZigBee coordinator
  to assign addresses to devices joining the
  network.
• Synchronization Ability of a node to
  synchronize with another node by listening for
  beacons or polling for data.
• Security Ability to ensure end-to-end integrity
  of frames.
• Routing Nodes can properly route frames to
  their destination (AODV, etc.).

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Application Support Layer Functions

• Zigbee Device Object (ZDO) maintains what the
  device is capable of doing and makes binding
  requests based on these capabilities.
• Discovery Ability to determine which other
  devices are operating in the operating space of
  this device.
• Binding Ability to match two or more devices
  together based on their services and their needs
  and allow them to communicate.

ZigBee Alliance Homepage
21
Routing
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Routing

• Ad hoc On Demand Distance Vector (AODV)
• Used for mesh topologies
• Cluster-Tree Algorithm
• Form clusters of nodes that make a tree

ZigBee Coordinator
ZigBee Router
ZigBee End Device
Heile, B. Wireless Sensor and Control Networks,
2006
23
RoutingTreebased Routing

• Routing only along parent-child links.
• Routers maintain their address and the address
  info associated with their children and parent.
• Given an address assignment in treebased network,
  router can determine if the destination belongs
  to a tree rooted at one of its router children or
  is one of its enddevice children
• If destination belongs to one of its children, it
  routes the packet to appropriate child.
• If destination does not belong to one of its
  children, it routes the packet to its parent

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Routing

• Simplified execution flow of the routing
  algorithm
• A device is said to have routing table capacity
  if
• It is a ZigBee coordinator or ZigBee router.
• It maintains a routing table.
• It has a free routing table entry or it already
  has a routing table entry corresponding to the
  destination

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RoutingRouter Discovery(1)

• Route Request message processing
• RREQ when node
• S wants to send
• packet to node D.
• - Setup forward
• router (to D).

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RoutingRouter Discovery(2)
No

• Route Reply message processing
• RREP from node D to
• node S

Yes
No
Yes
Yes
No
No
No
Yes
Yes
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Ad hoc On Demand Distance Vector (AODV)
D

• The Ad hoc On-Demand Distance Vector protocol is
  both an on-demand and a table-driven protocol.
• AODV supports multicasting and unicasting within
  a uniform framework.
• Each route has a lifetime after which the route
  expires if it is not used.
• A route is maintained only when it is used and
  hence old and expired routes are never used.

S
H. Karl, A. Willig Protocols and Architectures
for Wireless Sensor Networks, 2005
28
Cluster-Tree Algorithm

• Protocol of logical link and network layers.
• Forms single/multi cluster tree networks.
• Forms self-organizing network with redundancy and
  self-repair capabilities.
• Nodes select cluster heads and form clusters in a
  self-organized manner.
• Self-developed clusters then connect to each
  other through a designated Device (DD).

H. Karl, A. Willig Protocols and Architectures
for Wireless Sensor Networks, 2005
29
Security
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WSNs Security Requirements for WSN Security

• Data Confidentiality - omission of data leaks to
  neighboring networks. Relies on centralized
  infrastructure.
• Data Authentication - verification of
  sender/receiver.
• Data Integrity - non altered transmission of
  data.
• Data Freshness - ensuring data is recent while
  allowing for delay estimation.
• .

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WSNs Security Approaches to Security

• Key management and Trust setup
• Single network-wide key.
• Using pairwise-shared key.
• Hybrid-wide key approach.
• Trusted server approach.
• Asymmetric cryptography.
• Random key pre-distribution scheme.
• Cryptographic mechanisms
• Secure network encryption protocol (SNEP).

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ZigBee Security

• ZigBee is touted as highly secure
• Relies on centralized infrastructure
• Coordinator acts as trust center
• Types of keys
• Master key
• Installed out-of-band
• Network key
• Shared by all devices
• No protection against insider attacks
• Link key
• Derived from master key

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ZigBee Security Trust Center

• Can be the coordinator or a dedicated device on
  the network
• Trust during Join
• Authenticate join requests
• Network
• Updates and distributes network key
• End-to-End Configuration
• Assists link key setup

ZigBee Alliance, ZigBee Security Specification
Overview, 2005
34
Energy Efficiency
35
Energy Efficiency

• Connected Dominating Set (CDS) Approaches
• MAC Layer Approaches
• Slot-based Protocols.
• S-MAC and T-MAC.
• B-MAC.
• Cross Layer Approaches
• Network Support.
• Tree-based Stream Scheduling.
• Flexible Stream Scheduling.
• Topology Control
• A Model for Topology Control
• A Taxonomy of Topology Control Approaches

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Localization
37
Localization

• What is Localization in WSN ?
• Ability to determine the locations of sensors.
• Utilize some help from localization services like
  GPS.
• Importance of Localization
• Identifying the location of an event or a sensor
  of interest.
• Helping in routing and coverage optimization.
• Some Localization Challenges
• Accuracy VS Complexity/Cost
• Availability and Feasibility of accurate location
  systems. (e.g. GPS is not available indoor).

38
Localization Range-Based Methods

• Sensors calculate absolute point-to-point
  distance estimates (range) to anchors or angle
  estimates by utilizing one of the following
• Time of Arrival (TOA).
• Time Difference of Arrival (TDOA)
• Angle of Arrival (AOA)
• Received Signal Strength Indicator (RSSI)
• Utilize some help from localization services like
  GPS.
• Complex and depends on medium conditions and
  time synchronization
• High computational power or requirements in
  sensors.
• Too expensive for a large-scale WSN

TOA (GPS)
AOA
Wireless Sensor Network, An information
Processing Approach by F. Zhoa L. Guibas
39
Localization Range-Based Methods

• Sensors never tries to estimate the absolute
  point to-point distance between anchors and the
  sensors.
• Advantages
• Cheap sensor hardware.
• Low computational power
• Disadvantages
• Less accuracy than Region-Based methods

Wireless Sensor Network, An information
Processing Approach by F.Zhoa L.Guibas
40
ZigBee vs. Bluetooth

• ZigBee
• Smaller packets over large network.
• Data rate 250 Kbps _at_2.4
• GHz.
• Allows up to 254 nodes.
• Home automation, toys, remote controls, etc.

• Bluetooth
• Larger packets over Smaller network.
• Data rate 1Mbps _at_2.4
• GHz.
• Allows up to 7 nodes.
• Screen graphics, pictures, hands-free audio,
  Mobile phones, headsets, PDAs, etc.

ZigBee Alliance Homepage
41
What Does ZigBee Do?

• Designed for wireless controls and sensors
• Operates in Personal Area Networks (PANs) and
  device-to-device networks
• Connectivity between small packet devices
• Control of lights, switches, thermostats,
  appliances, etc.

ZigBee Alliance Homepage
42
References

• Paolo Baronti, Prashant Pillai, Vince Chook,
  Stefano Chessa, Alberto Gotta, Y.Fun Hu,
  Wireless Sensor Networks a Survey on the State
  of the Art and the 802.15.4 and ZigBee
  Standards, Computer Communication, Volume 30 ,
  Issue 7, pages 16551695,2007.
• ZigBee Alliance home page
• http//www.zigbee.org/en/index.asp
• IEEE 802.15.4 task group
• http//www.ieee802.org/15/pub/TG4.html
• Wireless Sensor Network, An information
  Processing Approach by F. Zhoa L.Guibas.
• H. Karl, A. Willig Protocols and Architecture for
  Wireless Sensor Networks,2005.
• Heile, B Wireless Sensor and Control Networks,
  2006

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Questions
Thank you !!