1. ZIGBEE WIRELESS NETWORKS

2. • WSN
• IEEE 802.15.4
• ZigBee

3. WSN
What is WSN?

4. WSN
• Wireless Sensor Network (WSN) is a network of small
spatially distributed devices that can communicate with each
other over the air

5. WSN
• to monitor
• to control
• both to monitor and control

6. WSN
• Application Areas
• less expensive
• more flexible

7. WSN
Opportunities

8. WSN
• Opportunities
• Unattended areas
• Large-scale networks with many nodes
• Increase reliability by rerouting possibility
• Mobility

9. Advanced Metering

10. Asset Tracking

11. Home Automation

12. Industrial Automation

13. WSN
Technology Requirements

14. WSN
• WSN Technology Requirements
• Low cost and small size devices
• Low power consumption
• Unlicensed radio bands
• Scalability: Support large number of nodes
• Flexibility: Simple deployment and network extension

16. ZigBee Bluetooth WiFi
Standard IEEE 802.15.4 IEEE 802.15.2 IEEE 802.11
Radio DSSS FHSS DSSS
Frequency 2.4GHz 2.4GHz 2.4/5GHz
Topology Star/Mesh/P2P Piconet Star/Mesh
Max Nodes 255/65000+ 7 30
Range ~50m ~10m ~100m
Duty Cycle Low Moderate Low to Moderate
Bandwidth 250Kbps 1Mbps 108Mbps

17. IEEE 802.15.4

18. !quot;#$%&(PHY)'(%)*+,&(MAC)'-./0&(Data Link)1
8 ZigBee Alliance 9:,;<=>?'-.@ABCD,'EFGHIJ
IEEE 802.15.4
STIJquot;
• LowRate-Wireless Personal
Area Network
• Physical
(PHY) and Medium
Access Control (MAC)

19. IEEE 802.15.4
• Type of network device
• Data transfer models
• Protocol stack
• Physical layer (PHY)
• Medium Access Control sub-layer (MAC)
• Functional overview

20. IEEE 802.15.4
Type of network devices

21. IEEE 802.15.4
• Types of network devices
• RFD (Reduced Functionality Device)
• FFD (Full Functionality Device)

22. IEEE 802.15.4
• RFD (Reduced Functionality Device)
• cancommunicate only to a single FFD in the network and
no RFDs
• requires
little memory, processing and power resource for
operation
• e.g., sensor nodes, actuator nodes

23. IEEE 802.15.4
• FFD (Full Functionality Device)
• capable to act as network coordinator and as an end-device
• can communicate both FFDs and RFDs
• requires
extra memory and processing power, consumes
more energy compared to RFD

24. IEEE 802.15.4
Data transfer models

25. IEEE 802.15.4
• Data transfer models
• Star
• Peer-to-peer
• *Mesh

26. IEEE 802.15.4
• Star
• networkis simple in set up
and deployment
• dataforwarding is possible
only by coordinator (two-
hop only)
• coveragearea is limited by
one-hop transmission
range

27. IEEE 802.15.4
• Peer-to-peer
• data frames can be
delivered via several
intermediate node
• largespatial areas can be
covered by a single
network
• complex packet routing
algorithm are required

28. IEEE 802.15.4
Protocol Stack

29. IEEE 802.15.4
• Physical layer (PHY)
• Medium Access Control
sub-layer (MAC)

30. IEEE 802.15.4
Physical layer

31. IEEE 802.15.4
• Physical layer
• activation and deactivation of the radio transceiver
• energy detection (ED) within the current channel
• link quality indicator (LQI) for received packets

32. IEEE 802.15.4
• channel frequency selection
• data transmission and reception
• clear
channel assessment (CCA) for carrier sense multiple
access with collision avoidance (CSMA-CA)

33. IEEE 802.15.4
• Physical layer (PHY)
• 802.15.4 PHY communication on 3 frequency bands:
Frequency Channels Data rates Availability Sensitivity
2450 16 250 Worldwide >= -85dBm
915 10 40, 250 US, AUS >= -92dBm
868 1 20, 100 Europe >= -92dBm

34. IEEE 802.15.4
• Physical layer
•a transmitter shall be capable of transmitting at least –3 dBm
(0.5 mW), normally at 0 dBm (1 mW)
•a receiver shall have a receiver maximum input level greater
than or equal to –20 dBm (0.01 mW)

35. IEEE 802.15.4
• Physical layer
• 2450MHz is the most commonly used band for WSNs
because:
• it’s available worldwide without need for licensing
• it has highest data rate achieved with simplest modulation
• Sub1-GHz bands (915/868 MHz) provide better signal
range than 2.4 GHz band

36. IEEE 802.15.4
• Physical layer
• when starting the network the coordinator scans pre-
configured channels and choose one with least activity
detected
• when joining the WPAN, a device scans through the given
set of channels and report discovered networks to higher
layers to permit join

38. IEEE 802.15.4
MAC layer

39. IEEE 802.15.4
• Medium Access Control sub-layer
• generating network beacons if the device is a coordinator
• synchronizing to network beacons
• supporting PAN association and disassociation

40. IEEE 802.15.4
• Medium Access Control sub-layer
• supporting device security
• employing the CSMA-CA mechanism for channel access
• handling and maintaining the GTS mechanism
• providing a reliable link between two peer MAC entities

41. IEEE 802.15.4
Functional Overview

42. IEEE 802.15.4
• Functional Overview
• Superframe structure
• Data transfer model
• Frame structure
• Improving probability of successful delivery
• Power consumption considerations
• Security

43. IEEE 802.15.4
Superframe structure

44. IEEE 802.15.4
• Superframe structure
• thisstandard allows the optional use of a superframe
structure. The format of the superframe is defined by the
coordinator. The superframe is bounded by network
beacons sent by the coordinator and is divided into 16
equally sized slots

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Supreframe structure without GTSs

46. IEEE 802.15.4
superframe can have an active and an
• Optionally, the
inactive portion. During the inactive portion, the
coordinator may enter a low-power mode. The beacon
frame is transmitted in the first slot of each superframe. If a
coordinator does not wish to use a superframe structure, it
will turn off the beacon transmissions

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Superframe structure without GTSs
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48. IEEE 802.15.4
• For low-latency applications or applications requiring specific
data bandwidth, the PAN coordinator may dedicate portions
of the active superframe to that application. These portions
are called guaranteed time slots (GTSs). The GTSs form
the contention-free period (CFP), which always appears
at the end of the active superframe starting at a slot boundary
immediately following the CAP

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50. Superframe structure with GTSs

51. IEEE 802.15.4
Data transfer model

52. IEEE 802.15.4
• Data transfer models
• type of data transfer transactions
• device -> coordinator
• coordinator -> device
• device -> device

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IEEE 802.15.4
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IEEE 802.15.4
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57. IEEE 802.15.4
• device -> device (Peer-to-peer)
• ina peer-to-peer PAN, every device may communicate with
every other device in its radio sphere of influence. In order
to do this effectively, the devices wishing to communicate
will need to either receive constantly or synchronize with
each other. In the former case, the device can simply
transmit its data using unslotted CSMA-CA. In the latter
case, other measures need to be taken in order to achieve
synchronization. Such measures are beyond the
scope of this standard

58. IEEE 802.15.4
Frame structure

59. IEEE 802.15.4
• Frame structure
• Beacon frame
• Data frame
• Acknowledgement frame
• MAC Command frame

60. IEEE 802.15.4
Beacon frame

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62. IEEE 802.15.4
Data frame

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64. IEEE 802.15.4
Acknowledgement frame

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Schematic view of the acknowledgment frame
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and the PHY packet

66. IEEE 802.15.4
MAC Command frame

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68. IEEE 802.15.4
Improving probability of successful delivery

69. IEEE 802.15.4
• Improving probability of successful delivery
• CSMA-CA mechanism
• Frame acknowledgement
• Data verification

70. IEEE 802.15.4
CSMA-CA Mechanism

71. IEEE 802.15.4
• CSMA-CA mechanism
• Beacon-enabled PAN
• slotted CSMA-CA
• Nonbeacon-enabled PAN
• Unslotted CSMA-CA

72. IEEE 802.15.4
Frame acknowledgement

73. IEEE 802.15.4
• Frame acknowledgement
•a successful reception and validation of a data or MAC
command frame can be optionally confirmed with an
acknowledgment. If the receiving device is unable to handle
the received data frame for any reason, the message is not
acknowledged

74. IEEE 802.15.4
• Frame acknowledgement
• ifthe originator does not receive an acknowledgment after
some period, it assumes that the transmission was
unsuccessful and retries the frame transmission. If an
acknowledgment is still not received after several retries, the
originator can choose either to terminate the transaction or
to try again. When the acknowledgment is not
required, the originator assumes the transmission
was successful

75. IEEE 802.15.4
Data verification

76. IEEE 802.15.4
• Data verification
• inorder to detect bit errors, an FCS mechanism employing a
16-bit International Telecommunication Union—
Telecommunication Standardization Sector (ITU-T) cyclic
redundancy check (CRC) is used to detect errors in
every frame

77. IEEE 802.15.4
Power consumption considerations

78. IEEE 802.15.4
• Power consumption considerations
devices will require duty-cycling to
• Battery-powered
reduce power consumption. These devices will spend most
of their operational life in a sleep state; however, each device
periodically listens to the RF channel in order to
determine whether a message is pending. This mechanism
allows the application designer to decide on the balance
between battery consumption and

79. IEEE 802.15.4
Security

80. IEEE 802.15.4
• Security
• The cryptographic mechanism in this standard is based on
symmetric-key cryptography and uses keys that are
provided by higher layer processes. The establishment and
maintenance of these keys are outside the scope of this
standard. The mechanism assumes a secure implementation
of cryptographic operations and secure and authentic
storage of keying material

81. ZIGBEE

82. ZIGBEE
• Protocol Stack
• Node Types
• Network Establishment
• Network Topologies

83. ZIGBEE
Protocol Stack

84. ZIGBEE
• Inorder to adopt WSN
technology for use in real-life
applications an association of
industry companies: ZigBee
Alliance has specified a full
protocol suite that provide
efficient high level
communication in WSNs

85. ZIGBEE
• ZigBee Alliance
• http://www.zigbee.org
• ZigBee Standard
• PHY & MAC = IEEE
802.15.4
• APS & NWK & APL

86. ZIGBEE
Node Types

87. ZIGBEE
• Node Types
• Coordinator
• Router
• End device

88. ZIGBEE
• Coordinator
•
• configuring key network parameters
• network start
• admission of other nodes
• network address assignment

89. ZIGBEE
• Router
•
•a node has IEEE 802.15.4 FFD capability but not act as
network coordinator is called a router
• to extend network coverage area beyond transmission
range of a single device
• to increase network reliability by creating data routing paths

90. ZIGBEE
• End device
•
• nodes of this type can directly communication only with a
single router or coordinator. Among other node types end
devices consume least processing, memory and power
resources and usually deployed on batteries in power saving
mode. Therefore ZigBee end devices correspond to reduced
functionality devices (RFD) in IEEE 802.15.4 standard

91. ZIGBEE
Network Establishment

92. ZIGBEE
• ZigBee network establishment
• Network layer (NWK) in ZigBee protocol stack extends
802.15.4 functionality in terms of possible node
interconnections, data transmission and network
management and provide mechanisms for exchange on the
level of entire network

93. ZIGBEE
Parent-child relationship

94. ZIGBEE
• Parent-child relationship
• child
- the node that has
entered the network
• parent- the node that has
provided network access

95. ZIGBEE
• Parent-child relationship
• only coordinator and routers can act as parent nodes
•a child node can have only one parent at a time
•a child node is able to change parent
• ZigBeenetwork hierarchy can be visualized as a tree with
coordinator being on top and end devices being tree leaves

96. ZIGBEE
• Parent-child relationship
• Basedon such hierarchical following parameters should be
specified by user to configure the network:
• Maximum number of direct children
• Maximum network depth

97. ZIGBEE
• Node addressing
• Each node that joins ZigBee network receives temporary
16-bit long network address (e.g., 3CB8). Communication
on network level is performed based on this address while
direct transmission between two neighboring devices is
done based on MAC address

98. ZIGBEE
Network Topologies

99. ZIGBEE
• Network Topologies
• Star
• Tree
• Mesh

100. ZIGBEE
• Star
• onlycoordinator can have
child nodes
• network coverage area is
limited by coordinator
transmission range
• networkis simple in setup
and deployment
• coordinatoris the only
node that can route data
packets

101. ZIGBEE
• Tree
• routers are able to have
child nodes
• directcommunication is
possible only in terms of
parent-child relation
• hierarchicalrouting
without alternative paths

102. ZIGBEE
• Mesh
• routers are able have child
nodes
• directcommunication is
possible between any FFD
devices within
transmission range of each
other
• optimum and dynamic
routing with alt paths