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

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

Standards

Final Presentation5 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

PHY Layer

MAC Layer

Network & Security

Application Framework

Applications

802.15.4

ZigBeeSpecification

Hardware

ZigBee stack

Application

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

http://www.zigbee.org/en/

4

ZigBee Responsibilities

• Designed for wireless controls and sensors

• Operates in Personal Area Networks (PAN’s) 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

ZigBee Alliance Homepage

• Direct Sequence Spread Spectrum (DSSS)• Channel switching, link quality estimation, energy detection

measurement and clear channel assessment to assist the channel selection


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

PreambleStart ofPacket

Delimiter

PHYHeader

PHY ServiceData Unit (PSDU)

6 Bytes 0-127 Bytes


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. CCA’s are aligned with the transmission/reception of the beacon.

10

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.

11

Guarantee Time Slot

IEEE 802.15.4 MAC Super-frame

Beacon

Inactive Period

GTSCAP

Active Period

Slot 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Beacon

Contention Access period

12


Beacon

Inactive Period

GTSCAP

Active Period

Slot 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Beacon

13


Beacon

Inactive Period

GTSCAP

Active Period

Slot 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Beacon

Data for node B

14


Beacon

Inactive Period

GTSCAP

Active Period

Slot 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Beacon

Ack

Store message

15


Beacon

Inactive Period

GTSCAP

Active Period

Slot 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Beacon

bacon ‘Data pending For B ‘

16


Beacon

Inactive Period

GTSCAP

Active Period

Slot 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Beacon

Data request

17


Beacon

Inactive Period

GTSCAP

Active Period

Slot 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Beacon

Data reply

18

ZigBee Functional Layers Architecture & Protocol Stack

19

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.).

20

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.


21

Routing

22

Routing

• Ad hoc On Demand Distance Vector (AODV)– Used for mesh topologies

• Cluster-Tree Algorithm– Form clusters of nodes that make a tree

ZigBee CoordinatorZigBee RouterZigBee 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

24

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

Packet to router

Packet addressed to this nod ?

Packet addressed to one of

end-device children ?

Is there a routing table entry for

the destination?

Are there resources to start a route discovery ?

Pass to higher layer

Route to child directly

Route to next hop

Initiate route discovery

Route along tree

No

No

No

No

Yes

Yes

Yes

Yes

25

RoutingRouter Discovery(1)

RREQ message

RDT entry existfor this RREQ

Create RDT entryand record fwd

path cost

Drop RREQ

Does RREQ report

a better fwd pathcost?

Update RDT entry Better fwd path cost

RREQ for local node

One of end-device Children?

Send RREP

Create RT entry(Discovery_Underway )and rebroadcast REEQ

Yes

Yes

Yes

No

No

No

• Route Request message processing

• RREQ when node

S wants to send

packet to node D.

- Setup forward

router (to D).

26

RoutingRouter Discovery(2)

RREP message

Are RDT and RT

entries available?

Drop REEP

Is local node

REEP destination?

Is RT entry status

Active ?

Does RREP report

a better residualpath cost?

Drop REEP

Does RREP report

a better residualpath cost?

Set RT entrystatus to Active

Update RDT entryresidual path cost and

RT entry next hop

Update RDT entryresidual path cost and

RT entry next hopForward RREP

• Route Reply message processing

• RREP from node D to

node S

Yes

Yes

Yes

Yes Yes

No

No

No No

No

27

Ad hoc On Demand Distance Vector (AODV)

• 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.

H. Karl, A. Willig Protocols and Architectures for Wireless Sensor Networks, 2005

S

D

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

30

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.

.

31

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).

32

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

33

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) ApproachesConnected Dominating Set (CDS) Approaches

• MAC Layer ApproachesMAC Layer Approaches– Slot-based Protocols.

– S-MAC and T-MAC.– B-MAC.

• Cross Layer ApproachesCross Layer Approaches– Network Support.

– Tree-based Stream Scheduling.

– Flexible Stream Scheduling.

• Topology ControlTopology Control– A Model for Topology Control

– A Taxonomy of Topology Control Approaches

36

Localization

37

Localization

• WhatWhat 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 @2.4

GHz.

• Allows up to 254 nodes.

• Home automation, toys, remote controls, etc.

Bluetooth• Larger packets over Smaller network.

• Data rate 1Mbps @2.4

GHz.

• Allows up to 7 nodes.

• Screen graphics, pictures, hands-free audio, Mobile phones, headsets, PDAs, etc.



41

What Does ZigBee Do?

• Designed for wireless controls and sensors• Operates in Personal Area Networks (PAN’s) and device-to-

device networks• Connectivity between small packet devices• Control of lights, switches, thermostats, appliances, etc.

securityHVAClighting controlaccess controllawn & garden irrigation

ZigBeeWireless Control that

Simply Works

RESIDENTIAL/LIGHT

COMMERCIAL CONTROL

CONSUMER ELECTRONIC

S

TVVCRDVD/CDremote

PERSONAL HEALTH

CARE

BUILDING AUTOMATION

securityHVAC

AMRlighting controlaccess control

patient monitoring

fitness monitoring



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

43

Thank you !!

Questions

Documents

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