discovered food source to her fellow

colony members.

CHARACTERISTICSCHARACTERISTICS Low costLow cost — Extends wireless to — Extends wireless to

virtually any sensor virtually any sensor

Low power consumptionLow power consumption — Ideal for — Ideal for

battery operation battery operation

Small size, light weight Small size, light weight — Easy to— Easy to

integrate integrate

Ease of implementation Ease of implementation

Reliable data transfer Reliable data transfer

Appropriate levels of security Appropriate levels of security

Direct sequence spread spectrumDirect sequence spread spectrum — —

Fast acquisition time Fast acquisition time

Range- 50m typical (5-500m based onRange- 50m typical (5-500m based on

environment)environment)

Multiple topologies- star, peer-to-peer,Multiple topologies- star, peer-to-peer,

mesh mesh

Data rates of 250 kbps (@2.4 GHz), 40Data rates of 250 kbps (@2.4 GHz), 40

kbps (@ 915 MHz), and 20 kbpskbps (@ 915 MHz), and 20 kbps

(@868 MHz) (@868 MHz)

ARCHITECHTUREARCHITECHTURE

ZigBee stack architectureZigBee stack architecture follows the follows the

standardstandard Open Systems Interconnection Open Systems Interconnection

(OSI) reference model; ZigBee's protocol(OSI) reference model; ZigBee's protocol

stack is structured in layers. The first twostack is structured in layers. The first two

layers, physical (PHY) and media accesslayers, physical (PHY) and media access

(MAC), are defined by the IEEE 802.15.4(MAC), are defined by the IEEE 802.15.4

standard. The layers above them arestandard. The layers above them are

defined by the ZigBee Alliance. defined by the ZigBee Alliance.

The model has five layers namely The model has five layers namely

1. Physical (PHY) layer 1. Physical (PHY) layer

2. Media access control (MAC) layer2. Media access control (MAC) layer

3. Network (NWK) and security layers3. Network (NWK) and security layers

4. Application framework 4. Application framework

5. Application profiles5. Application profiles

PHYSICAL LAYER:

ZigBee-compliant products operate

in unlicensed bands worldwide,

including 2.4GHz (global), 902 to

928MHz (Americas), and 868MHz

(Europe). Raw data throughput rates of

250Kbps can be achieved at 2.4GHz (16

channels), 40Kbps at 915MHz (10

channels), and 20Kbps at 868MHz (1

channel). The transmission distance is

expected to range from 10 to 75m,

depending on power output and

environmental characteristics. Like Wi-

FFiigguurree:: ZZiiggBBeeee SSttaacckk MMooddeell

Physical (PHY) Layer

Security Service Provider

PD-SAP

APSSE-SAP

NLSE-

SAP

PLME-SAP

Medium Access Layer (MAC) Layer

MLME-SAP MCPS-SAP

Network (NWK) Layer

NLME-SAP

NLDE-SAP

Application Support (APS) Layer

APSDE-SAP APSDE-SAP APSDE-SAP APSME-SAP

Application Framework

Application Object 240

[On Endpoint 240]

Application Object 1

[On Endpoint 1]

ZPUI

ZigBee Device Object (ZDO)

[On Endpoint 0]

Fi, Zigbee uses direct-sequence spread

spectrum in the 2.4GHz band, with

offset-quardrature phase-shift keying

modulation. Channel width is 2MHz

with 5MHzchannel spacing. The 868

and 900MHz bands also use direct-

sequence spread spectrum but with

binary-phase-shift keying modulation

Table: Frequency bands and data rates

PHY PHY FrequencFrequenc

y Band y Band

ChannelChannel

NumberinNumberin

gg

SpreadingSpreading

ParametersParametersData Parameters Data Parameters

ChipChip

RateRate

ModMod

ulatiulati

onon

BitBit

RateRate

SymSym

bolbol

RateRate

ModMod

ulatiulati

on on

868 to868 to

915915

MHz MHz

868 to868 to

870 MHz870 MHz00

300 k300 k

chip/schip/s

BPSBPS

KK

2020

kb/skb/s

20 k20 k

baudbaud

BPSBPS

KK

902 to902 to

928 MHz928 MHz1 to 101 to 10

600 k600 k

chip/schip/s

BPSBPS

KK

4040

kb/s kb/s

40 k40 k

baudbaud

BPSBPS

KK

2.42.4

GHzGHz

2.4 to2.4 to

2.48352.4835

GHz GHz

11 to 2611 to 262.0 M2.0 M

chip/schip/s

O-O-

QPSQPS

KK

250250

kb/s kb/s

62.562.5

kk

baud baud

16-16-

aryary

OrthOrth

ogonogon

al al

MEDIA ACCESS CONTROL LAYER

The media access control (MAC)The media access control (MAC)

layer was designed to allow multiplelayer was designed to allow multiple

topologies without complexity. Thetopologies without complexity. The

power management operation doesn'tpower management operation doesn't

require multiple modes of operation. Therequire multiple modes of operation. The

MAC allows a reduced functionalityMAC allows a reduced functionality

device (RFD) that needn't have flash nordevice (RFD) that needn't have flash nor

large amounts of ROM or RAM. Thelarge amounts of ROM or RAM. The

MAC was designed to handle largeMAC was designed to handle large

numbers of devices without requiring themnumbers of devices without requiring them

to be "parked". to be "parked".

The MAC provides network associationThe MAC provides network association

and disassociation, has an optionaland disassociation, has an optional

superframe structure with beacons for timesuperframe structure with beacons for time

synchronization, and a guaranteed time-synchronization, and a guaranteed time-

slot mechanism for high-priorityslot mechanism for high-priority

communicationscommunications

Frame structureFrame structure ::

Figure illustratesFigure illustrates the four basic frame the four basic frame

types defined in 802.15.4: data, ACK, types defined in 802.15.4: data, ACK,

MAC command, and beacon. MAC command, and beacon.

Figure:Figure:: The four basic frame types: The four basic frame types

defined in 802.15.4: Data, ACK, MACdefined in 802.15.4: Data, ACK, MAC

command, and beaconcommand, and beacon

The The data framedata frame provides a payload of up provides a payload of up

to 104 bytes. The frame is numbered toto 104 bytes. The frame is numbered to

ensure that all packets are tracked. Aensure that all packets are tracked. A

frame-check sequence ensures that packetsframe-check sequence ensures that packets

are received without error. This frameare received without error. This frame

structure improves reliability in difficultstructure improves reliability in difficult

conditions. conditions.

Another important structure for 802.15.4 isAnother important structure for 802.15.4 is

the the acknowledgment (ACK) frameacknowledgment (ACK) frame. It. It

provides feedback from the receiver to theprovides feedback from the receiver to the

sender confirming that the packet wassender confirming that the packet was

received without error. The device takesreceived without error. The device takes

advantage of specified "quiet time"advantage of specified "quiet time"

between frames to send a short packetbetween frames to send a short packet

immediately after the data-packetimmediately after the data-packet

transmission. transmission.

A A MAC command frameMAC command frame provides the provides the

mechanism for remote control andmechanism for remote control and

configuration of client nodes. Aconfiguration of client nodes. A

centralized network manager uses MAC tocentralized network manager uses MAC to

configure individual clients' commandconfigure individual clients' command

frames no matter how large the network. frames no matter how large the network.

Finally, the Finally, the beacon framebeacon frame wakes up client wakes up client

devices, which listen for their address anddevices, which listen for their address and

go back to sleep if they don't receive it.go back to sleep if they don't receive it.

Beacons are important for mesh andBeacons are important for mesh and

cluster-tree networks to keep all the nodescluster-tree networks to keep all the nodes

synchronized without requiring thosesynchronized without requiring those

nodes to consume precious battery energynodes to consume precious battery energy

by listening for long periods of time. by listening for long periods of time.

NETWORK LAYERNETWORK LAYER

ZigBee's self-forming and self-healingZigBee's self-forming and self-healing

mesh-network architecture lets data andmesh-network architecture lets data and

control messages pass from one node tocontrol messages pass from one node to

another by multiple paths. This featureanother by multiple paths. This feature

extends the network range and improvesextends the network range and improves

data reliability. It may also be used todata reliability. It may also be used to

build large, geographically dispersedbuild large, geographically dispersed

networks with smaller networks linked tonetworks with smaller networks linked to

form a 'cluster-tree' network. form a 'cluster-tree' network.

The NWK layer supports multiple networkThe NWK layer supports multiple network

topologies including star, cluster tree, and topologies including star, cluster tree, and

mesh, all of which are shown in mesh, all of which are shown in Figure Figure

In a star topology, one of the FFD-typeIn a star topology, one of the FFD-type

devices assumes the role of networkdevices assumes the role of network

coordinator and is responsible forcoordinator and is responsible for

initiating and maintaining the devices oninitiating and maintaining the devices on

the network. All other devices, known asthe network. All other devices, known as

end devices, directly communicate withend devices, directly communicate with

the coordinator. In a mesh topology, thethe coordinator. In a mesh topology, the

ZigBee coordinator is responsible forZigBee coordinator is responsible for

starting the network and for choosing keystarting the network and for choosing key

network parameters, but the network maynetwork parameters, but the network may

be extended through the use of ZigBeebe extended through the use of ZigBee

routers. The routing algorithm uses arouters. The routing algorithm uses a

request-response protocol to eliminate sub-request-response protocol to eliminate sub-

PAN coordinator Full Function Device Reduced Function Device

Star

Mesh

Cluster Tree

optimal routing. Ultimate network size canoptimal routing. Ultimate network size can

reach 264 nodes (more than we'll probablyreach 264 nodes (more than we'll probably

need). Using local addressing, you canneed). Using local addressing, you can

configure simple networks of more thanconfigure simple networks of more than

65,000 (216) nodes, thereby reducing65,000 (216) nodes, thereby reducing

address overheadaddress overhead

Security layerSecurity layer

Security and data integrity are key benefitsSecurity and data integrity are key benefits

of the ZigBee technology. ZigBeeof the ZigBee technology. ZigBee

leverages the security model of the IEEEleverages the security model of the IEEE

802.15.4 MAC sub-layer which specifies802.15.4 MAC sub-layer which specifies

four security services: access control—thefour security services: access control—the

device maintains a list of trusted devicesdevice maintains a list of trusted devices

within the network within the network

Data encryption, which usesData encryption, which uses

symmetric key 128-bit advancedsymmetric key 128-bit advanced

encryption standard encryption standard

Frame integrity to protect data fromFrame integrity to protect data from

being modified by parties withoutbeing modified by parties without

cryptographic keys cryptographic keys

Sequential freshness to reject dataSequential freshness to reject data

frames that have been replayed—theframes that have been replayed—the

network controller compares thenetwork controller compares the

freshness value with the last knownfreshness value with the last known

value from the device and rejects it ifvalue from the device and rejects it if

the freshness value has not beenthe freshness value has not been

updated to a new value updated to a new value

COMPARISION BETWEEN COMPARISION BETWEEN THE WIRELESS STANDARDSTHE WIRELESS STANDARDS

APPLICATIONS

Potential applications of zigbee include the

building automation, industrial, medical

and residential control & monitoring

A new twist on, "I've fallen and I

can't get up”

The figure basically shows a home-The figure basically shows a home-

monitoring system for senior citizens.monitoring system for senior citizens.

Zigbee-based sensors keep an eye onZigbee-based sensors keep an eye on

elderly residents living alone and warnelderly residents living alone and warn

medics about changes in habits that aremedics about changes in habits that are

potentially serious;potentially serious; It includes a lightIt includes a light

switch with a tiny digital camera (left); aswitch with a tiny digital camera (left); a

pendant (center) worn around the neck;pendant (center) worn around the neck;

and movement tags (right), which can letand movement tags (right), which can let

the system generate an alert based eitherthe system generate an alert based either

on detected movement or the lack of anyon detected movement or the lack of any

movement.movement.

Zigbee doesn't have the bandwidth to

handle video. So light switch / camera

combos deliver still images to a controller.

An alert from the pendant or from one of

the tags activates the camera.

The pendant includes accelerometers that

detect the forces of a person falling. It also

contains a panic button. The device can

send a warning either to a monitoring

company or family member if something

is up. It can be programmed to generate an

alert, for example, if a bedroom or

refrigerator door hasn't opened by noon.

The bugs this system catches aren't inThe bugs this system catches aren't in

softwaresoftware

One of the more offbeat

applications for Zigbee sensors is in

catching termites. Wireless bait stations

are devised which act as Zigbee nodes.

In operation, the bait stations go

into the ground at numerous spots

surrounding a house. Each bait station has

a special sensor that triggers when termites

eat at the wood it contains. The station

then signals this activity to a receiver,

which sends an e-mail.

This wireless approach beats theThis wireless approach beats the

technique now used on several levels.technique now used on several levels.

Existing methods force exterminators toExisting methods force exterminators to

physically check each station for activity.physically check each station for activity.

Termites could cause severe damage longTermites could cause severe damage long

before evidence of them could turn upbefore evidence of them could turn up

during a periodic inspection. In contrast,during a periodic inspection. In contrast,

the Zigbee bait stations monitor pestthe Zigbee bait stations monitor pest

activity 24/7. And exterminators need notactivity 24/7. And exterminators need not

make long trips just to examine baitmake long trips just to examine bait

stationsstations

Two key components of the

system are a base station and a Home

Key. The Key is envisioned to go into

your pocket or onto a key chain.

When the Key leaves the range of the

base station, it carries with it the last

status of items such as doors,

windows, and lights, as read by

sensors on the Zigbee network.

Homeowners wondering whether they

left the garage door open could

conceivably tell by looking at the

LCD in their Home Key. (However,

the system stops short of asking a

sympathetic neighbor to come over

and rectify the problem.)

The base station is smart enough to

notice if one of the sensors changes

state when the Home Key is out of

range. In this case it can send the

homeowner's cell phone a text

message detailing what's wrong.

A variety of sensors have been devised for

the system. In addition to proximity

switches for doors and windows, there are

devices designed to detect leaking pipes,

ac loads, and even remind homeowners

about periodic maintenance items such as

low batteries in smoke detectors or the

need for seasonal gutter cleaning. One

worthy piece of the system is a water shut-worthy piece of the system is a water shut-

off valve.off valve.

Zigbeef is a solution for trackingZigbeef is a solution for tracking

cattle. Zigbee sensors give beef producerscattle. Zigbee sensors give beef producers

the ability to electronically identify cattlethe ability to electronically identify cattle

whether their herds are crowded intowhether their herds are crowded into

chutes, gathered into pens, or grazing openchutes, gathered into pens, or grazing open

pasture.pasture. ZigBeef radio-based cattle earZigBeef radio-based cattle ear

tags offertags offer superior reading-range oversuperior reading-range over

passive wand-based tag technology.passive wand-based tag technology.

Producers are no longerProducers are no longer limited tolimited to

infrequent opportunities to scaninfrequent opportunities to scan

IDs.IDs. ZigBeef allowsZigBeef allows identification of eachidentification of each

animalanimal on the range, pen, or workingon the range, pen, or working

chute, at virtually any time. ZigBeef tagschute, at virtually any time. ZigBeef tags

use mass-produced, non-proprietaryuse mass-produced, non-proprietary

wireless sensor technologies, offering awireless sensor technologies, offering a

proven solution at an inexpensive price.proven solution at an inexpensive price.

[refer the greeting preview for the figure].[refer the greeting preview for the figure].

CONCLUSION

There are many wireless monitoring and

control applications for industrial and

home markets which require longer battery

life, lower data rates and less complexity

than available from existing wireless

standards like Bluetooth and Wi-Fi. So,

there was a need for a standard based,

interoperable wireless technology that

addresses the unique needs of low data rate

wireless control and sensor based

networks. In this regard, zigbee was poised

to become the global control/sensor

network standard.

Zigbee promises to put wireless sensors in

everything from factory automation

systems to home security systems to

consumer electronics. Zigbee is a new

standard that still needs to pass through the

circles or rigorous technology critics and

establish its own place in the industry. The

next zigbee challenge will be devising the

proposed extension to the 802.15.4

standard,’4a’ which could be based on

ultra-wideband (UWB).

REFERENCES

1. Electronics for you- November 2004

2. Computer networks-by Tanenbaum

3. www.zigbeealliance.com4. www.zigbee.org5. www.zigbeef.com6. www.nuri.com

http://www.nuri.com/

http://www.zigbeef.com/

http://www.zigbee.org/

http://www.zigbeealliance.com/

zig bee network

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