Transcript 563.0 Introduction - uni

Wireless Sensor Networks:
a Survey on the State of the Art
and the 802.15.4 and ZigBee
Standards
Final Presentation
5 August 2008
Omer Alkhnbashi
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.
2
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.
Applications
Application Framework
ZigBee
Specification
Network & Security
Application
MAC Layer
802.15.4
PHY Layer
Motorola : www.motorola.com/zigbee
ZigBee stack
Hardware
3
ZigBee Responsibilities
• Designed for wireless controls and sensors
• Operates in Personal Area Networks (PAN’s) and device-todevice networks
• Connectivity between small packet devices
• Control of lights, switches, thermostats, appliances, etc.
4
Why do we need ZigBee
technology?
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.
5
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
6
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
Preamble
Start of
Packet
Delimiter
6 Bytes
ZigBee Alliance Homepage
PHY
Header
PHY Service
Data Unit (PSDU)
0-127 Bytes
7
IEEE 802.15.4 MAC
Device 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
8
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. CCA’s 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
Beacon
Beacon
CAP
GTS
Inactive Period
Slot 0 1 2
3
4
5
6
7
8
9 10 11 12 13 14 15
Active Period
Contention Access period
Guarantee Time Slot
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IEEE 802.15.4 MAC
Super-frame
Beacon
Beacon
CAP
GTS
Inactive Period
Slot 0 1 2
3
4
5
6
7
8
9 10 11 12 13 14 15
Active Period
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IEEE 802.15.4 MAC
Super-frame
Data for node B
Beacon
Beacon
CAP
GTS
Inactive Period
Slot 0 1 2
3
4
5
6
7
8
9 10 11 12 13 14 15
Active Period
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IEEE 802.15.4 MAC
Super-frame
Ack
Store message
Beacon
Beacon
CAP
GTS
Inactive Period
Slot 0 1 2
3
4
5
6
7
8
9 10 11 12 13 14 15
Active Period
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IEEE 802.15.4 MAC
Super-frame
bacon ‘Data pending
For B ‘
Beacon
Beacon
CAP
GTS
Inactive Period
Slot 0 1 2
3
4
5
6
7
8
9 10 11 12 13 14 15
Active Period
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IEEE 802.15.4 MAC
Super-frame
Data request
Beacon
Beacon
CAP
GTS
Inactive Period
Slot 0 1 2
3
4
5
6
7
8
9 10 11 12 13 14 15
Active Period
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IEEE 802.15.4 MAC
Super-frame
Data reply
Beacon
Beacon
CAP
GTS
Inactive Period
Slot 0 1 2
3
4
5
6
7
8
9 10 11 12 13 14 15
Active Period
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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
20
Routing
21
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
22
Routing
Treebased 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
Packet to router
• 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
Packet addressed
to this nod ?
Yes
Pass to higher layer
No
Packet
addressed to one of
end-device
children ?
No
Is there a routing
table entry for
the destination
?
No
Are there
resources to
start a route
discovery ?
No
Yes
Route to child directly
Yes
Route to next hop
Yes
Initiate route discovery
Route along tree
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Routing
Router Discovery(1)
RREQ message
Yes
• Route Request message
processing
Does
• RREQ when node
RREQ report
a better fwd path
S wants to send
cost?
packet to node D.
No
- Setup forward
Drop RREQ
router (to D).
RDT entry exist
for this RREQ
Yes
No
Create RDT entry
and record fwd
path cost
Update RDT entry
Better fwd path cost
Yes
Send RREP
RREQ
for local node
One of end-device
Children?
No
Create RT entry
(Discovery_Underway )
and rebroadcast REEQ
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Routing
Router Discovery(2)
Are
RDT and RT
entries available
RREP message
• Route Reply message
processing
• RREP from node D to
node S
No
Drop REEP
?
Yes
Yes
Is
RT entry status
Active ?
No
Set RT entry
status to Active
Is
local node
REEP destination
?
Yes
No
Does
RREP report
a better residual
path cost?
No
Drop REEP
Yes
Update RDT entry
residual path cost and
RT entry next hop
Forward RREP
No
Does
RREP report
a better residual
path cost?
Yes
Update RDT entry
residual path cost and
RT entry next hop
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Ad hoc On Demand Distance Vector
(AODV)
• The Ad hoc On-Demand Distance
Vector protocol is both an ondemand 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.
H. Karl, A. Willig Protocols and Architectures for Wireless Sensor Networks, 2005
D
S
27
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
28
Security
29
WSN’s 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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WSN’s 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
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Energy Efficiency
34
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
35
Localization
36
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).
37
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.
TOA (GPS)
• Complex and depends on medium conditions and
time synchronization
– High computational power or requirements in sensors.
– Too expensive for a large-scale WSN
AOA
Wireless Sensor Network, An information Processing Approach by F. Zhoa & L. Guibas
38
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
39
ZigBee vs. Bluetooth
ZigBee
Bluetooth
•
Smaller packets over large network.
•
Larger packets over Smaller network.
•
Data rate 250 Kbps @2.4
GHz.
•
Data rate 1Mbps @2.4
GHz.
•
Allows up to 254 nodes.
•
Allows up to 7 nodes.
•
Home automation, toys, remote
controls, etc.
•
Screen graphics, pictures, hands-free
audio, Mobile phones, headsets,
PDAs, etc.
ZigBee Alliance Homepage
40
What Does ZigBee Do?
• Designed for wireless controls and sensors
• Operates in Personal Area Networks (PAN’s) and device-todevice networks
• Connectivity between small packet devices
• Control of lights, switches, thermostats, appliances, etc.
security
HVAC
AMR
lighting control
access control
BUILDING
AUTOMATION
ZigBee
CONSUMER
ELECTRONIC
S
Wireless Control that
Simply Works
patient
monitoring
fitness
monitoring
ZigBee Alliance Homepage
PERSONAL
HEALTH
CARE
RESIDENTIAL/
LIGHT
COMMERCIAL
CONTROL
TV
VCR
DVD/CD
remote
security
HVAC
lighting control
access control
lawn & garden
irrigation
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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
42
Questions
Thank you !!
43