Zigbee

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Zig Bee

systems to home security systems to consumer electronics.

INTRODUCTION ZigBee

is

technology,

a

low-power

rewriting

the

wireless

sensor equation. It is a secure network technology that rides on top of the recently ratified IEEE 802.15.4 radio standard. It is designed to interact with the remote controlled devices, which are put under a single standardized control interface that can interconnect into a network.

Once

ORIGIN OF THE NAME ZIGBEE

wireless

associated

with

a

network, a ZigBee node can wake up and communicate with other ZigBee devices and return to sleep.

The network name comes from the zigzagging path a bee (a data packet) takes to get from flower to flower (or node to node). The technique that honeybees

use

newfound

food

communicate

sources

to

other

members of the colony is referred to as the ZigBee Principle. Using this silent, but powerful communication system, whereby the bee dances in a zigzag pattern,

they

information

Zigbee’s key technical features include three license free frequency bands2.4GHz, 868MHz, 915MHz;multiple channels; up to 100mts range; CSMACA channel access; low power, long battery life; supporting up to 255devices per network.

to

are

such

able as

the

to

share

location,

distance, and direction of a newly discovered food source to her fellow colony members.

Zigbee is used in home security systems where

wireless

sensors

are

easily

installed than sensors that need wiring. The

same

is

true

in

CHARACTERISTICS

industrial

environments, where wiring typically

•

virtually any sensor

accounts for 80% of the cost of sensor installations.

And

then

there

are

•

applications for sensors where wiring isn't practical or even possible. ZigBee promises to put wireless sensors in 1 Email: [email protected]

Low cost — Extends wireless to Low power consumption — Ideal for battery operation

•

Small size, light weight — Easy to integrate

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Ease of implementation

•

Reliable data transfer

•

Appropriate levels of security

•

Direct sequence spread spectrum — Fast acquisition time

•

Range- 50m typical (5-500m based on environment)

•

PHYSICAL LAYER:

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

•

ZigBee-compliant products operate in

unlicensed

bands

worldwide,

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

including 2.4GHz (global), 902 to

kbps (@ 915 MHz), and 20 kbps

928MHz

(@868 MHz)

(Europe). Raw data throughput rates of

(Americas),

and

868MHz

250Kbps can be achieved at 2.4GHz (16

ARCHITECHTURE

channels), 40Kbps at 915MHz (10

ZigBee stack architecture follows the

channels), and 20Kbps at 868MHz (1

standard Open Systems Interconnection

channel). The transmission distance is

(OSI) reference model; ZigBee's protocol

expected to range from 10 to 75m,

stack is structured in layers. The first two

depending

layers, physical (PHY) and media access

environmental characteristics. Like Wi-

(MAC), are defined by the IEEE 802.15.4

Fi, Zigbee uses direct-sequence spread

standard. The layers above them are

spectrum in the 2.4GHz band, with

defined by the ZigBee Alliance.

offset-quardrature

The model has five layers namely

on

power

output

phase-shift

and

keying

modulation. Channel width is 2MHz

1. Physical (PHY) layer

with 5MHzchannel spacing. The 868

2. Media access control (MAC) layer

and 900MHz bands also use direct-

3. Network (NWK) and security layers

sequence spread spectrum but with

4. Application framework

binary-phase-shift keying modulation

ApplicationFramework

5. Application profiles

Security Service Provider

AP SS ESA P

NL SE SA P

ZP UI

ZigBee Device Object (ZDO)

Application Object 240

Application Object 1

[On Endpoint 240]

[On Endpoint 1]

[On Endpoint 0]

APSDE-SAP

APSDE-SAP

APSDE-SAP

Application Support (APS) Layer NLDE-SAP

NL M ESA P

Network (NWK) Layer MCPS-SAP

AP S M ESA P

MLME-SAP

MediumAccess Layer (MAC) Layer

2 Email: [email protected] PD-SAP

PLME-SAP

Physical (PHY) Layer Figure: ZigBee Stack Model

Table: Frequency bands and data rates Frequency

Spreading

Band

Parameters

Data Parameters

Visit: www.geocities.com/chinna_chetan05/forfriends.html Channel Numberin g 868 to 915 MHz

868 to 870 MHz 902 to 928 MHz

0

1 to 10

Chip Rate

Mod ulatio n

Bit Rate

Sym

Mod

types defined in 802.15.4: data, ACK, MAC command, and beacon.

bol

ulatio

Rate

n

300 k

BPS

20

20 k

BPS

chip/s

K

kb/s

baud

K

600 k

BPS

40

40 k

BPS

chip/s

K

kb/s

baud

K 16-

2.4 GHz

2.4 to 2.4835

11 to 26

GHz

2.0 M chip/s

OQPS K

250 kb/s

62.5

ary

k

Orth

baud

ogon al

MEDIA ACCESS CONTROL LAYER The media access control (MAC) layer was designed to allow multiple topologies without power

management

complexity. The operation

doesn't

Figure:: Figure:: The four basic frame types defined in 802.15.4: Data, ACK, MAC command, and beacon

require multiple modes of operation. The MAC allows a reduced functionality device (RFD) that needn't have flash nor

The data frame provides a payload of up

large amounts of ROM or RAM. The

to 104 bytes. The frame is numbered to

MAC was designed to handle large

ensure that all packets are tracked. A

numbers of devices without requiring them

frame-check sequence ensures that packets

to be "parked".

are received without error. This frame structure improves reliability in difficult

The MAC provides network association and

disassociation,

has

an

conditions.

optional

superframe structure with beacons for time

Another important structure for 802.15.4 is

synchronization, and a guaranteed time-

the acknowledgment (ACK) frame. frame. It

slot

provides feedback from the receiver to the

mechanism

for

high-priority

communications

sender confirming that the packet was received without error. The device takes

Frame structure:

advantage

Figure illustrates the four basic frame

between frames to send a short packet

3 Email: [email protected]

of

specified

"quiet

time"

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after

the

data-packet

transmission. A MAC command frame provides the mechanism configuration

for of

remote

control

client

and

nodes.

A

centralized network manager uses MAC to configure individual clients' command frames no matter how large the network. Finally, the beacon frame wakes up client devices, which listen for their address and go back to sleep if they don't receive it. Beacons are important for mesh and cluster-tree networks to keep all the nodes synchronized

without

requiring

those

nodes to consume precious battery energy by listening for long periods of time.

The NWK layer supports multiple network topologies including star, cluster tree, and mesh, all of which are shown in Figure In a star topology, one of the FFD-type devices assumes the role of network coordinator

and

is

responsible

for

initiating and maintaining the devices on the network. All other devices, known as end devices, directly communicate with the coordinator. In a mesh topology, the ZigBee coordinator is responsible for starting the network and for choosing key network parameters, but the network may be extended through the use of ZigBee routers. The routing algorithm uses a request-response protocol to eliminate sub-

NETWORK LAYER

optimal routing. Ultimate network size can

ZigBee's self-forming and self-healing mesh-network architecture lets data and control messages pass from one node to another by multiple paths. This feature extends the network range and improves data reliability. It may also be used to build

large,

geographically

reach 264 nodes (more than we'll probably need). Using local addressing, you can configure simple networks of more than 65,000 (216) nodes, thereby reducing address overhead Security layer

dispersed

networks with smaller networks linked to

Security and data integrity are key benefits

form a 'cluster-tree' network.

of

the

ZigBee

technology.

ZigBee

leverages the security model of the IEEE Mesh

802.15.4 MAC sub-layer which specifies four security services: access control—the

Star

PAN coordinator

4 Email: [email protected] Full Function Device

Cluster Tree

Reduced Function Device

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Potential applications of zigbee include the

within the network

building automation, industrial, medical and residential control & monitoring

•

Data

encryption,

symmetric

key

which

128-bit

uses

advanced

encryption standard

A new twist on, "I've fallen and I can't get up” The figure basically shows a home-

•

Frame integrity to protect data from

monitoring system for senior citizens.

being modified by parties without

Zigbee-based sensors keep an eye on

cryptographic keys

elderly residents living alone and warn medics about changes in habits that are

•

Sequential freshness to reject data

potentially serious; It

includes a light

frames that have been replayed—the

switch with a tiny digital

camera (left); a

network

pendant (center) worn

controller

compares

the

around the neck;

freshness value with the last known

and movement tags (right), which can let

value from the device and rejects it if

the system generate an alert based either

the freshness value has not been

on detected movement or the lack of any

updated to a new value

movement.

COMPARISION BETWEEN THE WIRELESS STANDARDS

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 APPLICATIONS 5 Email: [email protected]

detect the forces of a person falling. It also contains a panic button. The device can

Visit: www.geocities.com/chinna_chetan05/forfriends.html 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 in software One of the more offbeat applications for Zigbee sensors is in catching termites. Wireless bait stations are devised which act as Zigbee nodes.

Two key components of the system are a base station and a Home

In operation, the bait stations go into

the

ground at numerous

Key. The Key is envisioned to go into

spots

your pocket or onto a key chain.

surrounding a house. Each bait station has

When the Key leaves the range of the

a special sensor that triggers when termites

base station, it carries with it the last

eat at the wood it contains. The station

status

then signals this activity to a receiver,

windows, and lights, as read by

which sends an e-mail.

sensors on the Zigbee network.

of

items

such

as

doors,

Homeowners wondering whether they This wireless approach beats the technique now used on several levels. Existing methods force exterminators to physically check each station for activity. Termites could cause severe damage long before evidence of them could turn up

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.)

during a periodic inspection. In contrast,

The base station is smart enough to

the Zigbee bait stations monitor pest

notice if one of the sensors changes

activity 24/7. And exterminators need not

state when the Home Key is out of

make long trips just to examine bait

range. In this case it can send the

stations

homeowner's

cell

phone

a

message detailing what's wrong. 6 Email: [email protected]

text

Visit: www.geocities.com/chinna_chetan05/forfriends.html A variety of sensors have been devised for

Zigbeef is a solution for tracking

the system. In addition to proximity

cattle. Zigbee sensors give beef producers

switches for doors and windows, there are

the ability to electronically identify cattle

devices designed to detect leaking pipes,

whether their herds are crowded into

ac loads, and even remind homeowners

chutes, gathered into pens, or grazing open

about periodic maintenance items such as

pasture. ZigBeef radio-based cattle ear

low batteries in smoke detectors or the

tags offer superior reading-range over

need for seasonal gutter cleaning. One

passive

worthy piece of the system is a water shut-

Producers

off valve.

infrequent

wand-based are

no

tag

technology.

longer limited

opportunities

to

to scan

IDs. ZigBeef allows identification of each animal on the range, pen, or working chute, at virtually any time. ZigBeef tags use

mass-produced,

non-proprietary

wireless sensor technologies, offering a proven solution at an inexpensive price. [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

network standard.

7 Email: [email protected]

global

control/sensor

Visit: www.geocities.com/chinna_chetan05/forfriends.html 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.com 4. www.zigbee.org 5. www.zigbeef.com 6. www.nuri.com

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