Article about ZigBee by David Geer

Page 1

Computer

I N D U S T R Y T R E N D S

Published by the IEEE Computer Society

s wireless-sensor technology

improves, an increasing num-

ber of organizations are using

it for a wide range of pur-

poses. Users are working

with the technology to monitor and

automate home, building, industrial,

and agricultural systems, including

thermostats and security products,

said Mareca Hatler, director of

research for ON World, a market

research firm.

In addition, they are working with

sensor networks for checking on envi-

ronmental quality and the integrity

of bridges and other structures, auto-

mated meter reading, and even in

home healthcare, national security, and

military networks, she added.

“ON World forecasts 127 million

deployed wireless sensing network

nodes in 2010, up from 1.2 million in

2005,” she noted.

To achieve technological and mar-

ketplace success, the low-power, inex-

pensive sensor networks need an eco-

nomical, low-latency, robust, energy-

efficient, wireless connectivity infra-

structure. With this in mind, users are

increasingly working with ZigBee tech-

nology.

Other prominent wireless technolo-

gies, such as Bluetooth, don’t fit the bill

because, for example, they are too

expensive or use too much energy.

Bluetooth is designed to connect high-

volume, packet-based devices such as

laptops, phones, and major peripher-

als. ZigBee, on the other hand, con-

nects low-volume devices such as sen-

sors and works with simpler, less

expensive, easy-to-use technology.

The ZigBee Alliance (www.zigbee.

org) promotes use of the technology,

and its 200 members are currently con-

ducting interoperability tests and releas-

ing products. Specification-compliant

products receive a ZigBee Alliance logo,

noted Nick Dutton, director of business

development for Integration Associates,

a semiconductor design company and

alliance member.

However, ZigBee faces competition

from other technologies, as well as

marketplace confusion.

INSIDE ZIGBEE

In 1999, the Firefly Working Group,

no longer in existence, originated the

technology that would become ZigBee.

Today’s ZigBee is built on the IEEE

802.15.4 low-rate, wireless, personal-

area-network standard, adopted in

2003. The ZigBee Alliance ratified the

first ZigBee standard in December

2004 and released it to the public in

June of this year.

Technology

Although IEEE 802.15.4 supports

mesh and other network technologies,

the specification itself operates peer to

peer. However, adding network-layer

specifications can introduce other

capabilities. For example, adding

ZigBee atop the 802.15.4 stack lets the

technology work directly with other

network topologies such as mesh,

explained Dutton. ZigBee also adds

security to the IEEE standard, as

Figure 1 shows.

ZigBee additionally defines the nature

of its data communications and routing

within networks, as well as the way

nodes discover one another.

ZigBee uses IEEE 802.15.4’s bea-

coning technique—in which a node

continuously transmits small packets

to advertise its presence to other

mobile units, which then try to estab-

lish a connection—to start networks

and let other devices join in, added

Philip Orlik, principal technical staff

member with the Mitsubishi Electric

Research Laboratories (MERL).

The technology also works with

the routing discovery approach that

ad hoc on-demand networks use,

explained Orlik. When a sending node

needs a route to a destination, it broad-

casts a route-request packet across the

network. Nodes then set up backward

pointers to the source node in the route

tables. The system then builds routes

between nodes and maintains them as

long as they are needed.

Spectrum and transmission range.

ZigBee uses the same unlicensed 2.4-

GHz (worldwide), 868-MHz (in

Europe), and 915-MHz (in the

Americas) radio bands as many cord-

less telephones. These bands work well

for low-cost sensor networks because

users don’t have to obtain licenses and

the spectrum is widely available.

The technology’s transmission

ranges are 10 meters indoors and 200

meters outdoors for devices using the

2.4-GHz band, and 30 meters indoors

and 1,000 meters outdoors for devices

using the other bands, according to

Dutton.

Users Make a

Beeline for ZigBee

Sensor Technology

David Geer

Page 2

development director at semiconduc-

tor vendor Chipcon.

And because each node can take care

of the necessary switching and routing,

ZigBee networks don’t need separate

equipment such as hubs and routers,

and thus they can handle network traf-

fic economically.

Implementation

ZigBee is implemented in a device or

other node via chips. Currently, ZigBee

devices need only an 8-bit controller

chip that includes some networking

and security functionality; a trans-

ceiver chip, which has the radio func-

tionality; a power source; and a few

passive components.

Chip makers such as Chipcon and

Ember are beginning to combine the

controller and transceiver circuitry

onto one piece of silicon.

ZigBee’s simplicity and plug-and-

play capabilities make implementing

the technology inexpensive and easy,

particularly because it requires little or

no network engineering.

And organizations can use gateways

to easily integrate ZigBee technology

with their back-end maintenance,

building automation, automated meter

Data rates. ZigBee transmits data at

a relatively slow 250 Kbits per second

at 2.4 GHz, 40 Kbps at 915 MHz, and

20 Kbps at 868 MHz, which works

well for simple sensor systems that

transmit only small amounts of data

occasionally, said Orlik. This is con-

siderably slower than other wireless

connectivity technologies such as

Bluetooth and far too slow for other

wireless purposes such as transmitting

real-time video.

Security. For security, ZigBee uses

128-bit Advanced Encryption Standard

cryptography and trust-center-based

authentication, according to David

McCartney, vice president of sales and

marketing for software vendor Airbee

Wireless. A trust center admits devices

to a network and hands out ZigBee

device and network authentication

keys, he explained.

Nodes. Theoretically, ZigBee can

support up to 65,536 nodes. However,

supporting this many nodes makes

network administration unmanage-

able. To avoid this problem, Dutton

said, ZigBee networks should have no

more than 3,000 nodes. For situations

requiring more nodes, he explained,

multiple subnets would work better

than trying to make a single large net-

work even bigger.

Low latency. ZigBee is optimized for

time-critical applications that won’t

tolerate latency, such as lighting and

power-management controls. ZigBee

devices don’t have to synchronize with

other nodes on a network before join-

ing and beginning communications.

Thus, devices require only 30 mil-

liseconds to join a network and 15

milliseconds to access and start com-

municating with other nodes.

Energy efficiency. Because ZigBee per-

forms just a few specific, simple tasks,

the protocol stack can be as small as 28

Kbytes. Thus, system controllers need

less memory and consume less power.

In addition, ZigBee devices transmit

small amounts of simple data, like

those from sensors, which minimizes

the amount of energy the systems use,

Dutton noted.

Also, he said, ZigBee activates de-

vices only when they’re needed to pass

or act on data, which also contributes

to power efficiency.

ZigBee can thus let batteries in

devices run for a long time, which is

critical for install-and-forget sensor-

related tasks such as wireless monitor-

ing and control systems.

Mesh networking

ZigBee uses a full mesh topology,

in which all nodes connect to and

communicate directly with other

nodes within range. Only the in-

tended recipient acts on the transmit-

ted data.

This approach avoids problems—

experienced by nonmesh networks

that require clear lines of sight between

nodes—in which obstacles block radio

signals. This is an important consider-

ation in factories or warehouses full of

equipment and shelves.

Mesh networking also lets commu-

nications pass through any set of nodes

between the sender and receiver, which

is helpful if a node breaks down or is

removed from service. This makes

ZigBee networks self-healing, noted

Graham Martin, ZigBee business

December 2005

Applications

Application profiles

Application framework

Network and security

layers

Media access control

Layer

Physical layer

Silicon

ZigBee stack

Application

Source: ZigBee Alliance

User

ZigBee application profiles

IEEE 802.15.4

ZigBee-

compliant

platform

Figure 1. ZigBee is built on the robust physical and media-access-control layers defined by

the IEEE 802.15.4 standard. Above these layers, ZigBee defines a mesh network topology

with security features and interoperable application profiles.

Page 3

Computer

writing profiles that will work only with

their own applications.

ZigBee could have many other poten-

tial uses, such as transmitting tempera-

ture readings from thermostats; on and

off requests for wireless light switches,

which could eliminate the expensive

and time-consuming wiring that tradi-

tional switches require; or keystrokes

from a wireless keyboard.

Because of its low cost, easy installa-

tion, and many potential uses, ZigBee

would particularly appeal to builders

and homeowners, said Chipcon’s

Martin.

ZigBee-based monitors could track

senior citizens living alone and warn

medical personnel about changes that

could indicate health or safety prob-

lems. ZigBee-powered sprinkler systems

could use just enough water to keep

plants green. The technology could even

enable fleet-management systems to

report on vehicle maintenance status,

tire conditions, and mileage.

ZIGZAGGING AROUND OBSTACLES

Widespread ZigBee adoption faces

several challenges.

Competition

ZigBee must cope with marketplace

competition from technologies such as

reading, energy management, and

other systems.

“Integrating wireless sensor net-

works with other systems is essential

to the end user in enabling them to not

only collect sensor information but

also translate it into useful information

for data analytics, remote control, and

monitoring applications,” explained

ON World’s Hatler. “Wireless sensor

networks connected to gateways that

are in turn connected to wide area net-

works enable the sensor information

to be transmitted many miles away for

processing in a faraway office.”

Uses

The ZigBee Alliance is devising

application profiles, which let pro-

grammers use application-specific

commands when setting up ZigBee

controllers for related sets of tasks.

The first profile, recently completed,

addresses lighting applications and

includes information needed to enable

dimmers, switches, and lights to com-

municate with one another, according

to ZigBee Alliance chair Bob Heile.

The Alliance will soon release profiles

for heating, ventilation, and air condi-

tioning; industrial process control; and

building automation, he noted. And

some companies like Honeywell are

Zensys’s Z-Wave and Smarthome’s

Insteon, which perform many of the

same functions.

Z-Wave (www.z-wavealliance.com)

and Insteon (www.insteon.net) are

proprietary wireless technologies

designed mainly for home control and

automation.

Z-Wave uses low-power mesh-net-

worked transmitters and repeaters.

Insteon uses radio technology and a

home’s existing electrical wiring. It

works on a peer-to-peer basis and is

not routed, like ZigBee and Z-Wave.

Insteon thus doesn’t require network

controllers.

Proponents of the two technologies

claim they are better than ZigBee for

the residential uses for which they were

designed.

For example, because ZigBee was

designed to work with many applica-

tions in both home and industrial set-

tings, the technology’s radios will

require more memory and thus will cost

more, said Raoul Wijgergangs, Zensys’s

vice president of business development.

Also, the chips will be bigger and more

expensive and, therefore, less practical

for home use, he added.

Confused marketplace

“Due to the wide range of applica-

tions and types of end users, there are

many proprietary solutions today that

confuse the marketplace by calling

themselves ‘ZigBee-ready,’ ” noted ON

World’s Hatler.

However, she predicted that users

who want ZigBee functionality even-

tually will support only products that

use technology based on the standard.

MOVING AHEAD

The ZigBee Alliance is looking at

ways to bridge its technology with

other types of wireless and wired net-

works, such as those based on Wi-Fi.

Interacting with other types of net-

works would broaden their usefulness,

according to Heile.

For example, bridging could take

advantage of both ZigBee’s and other

networks’ capabilities and eliminate

I n d u s t r y T r e n d s

Source: Gartner Dataquest

Units (millions)

100

120

140

160

2006

2007

2008

2009

2005

2010

Figure 2. Gartner Dataquest, a market research firm, predicts rapidly growing ZigBee

adoption during the next five years.

Page 4

the need for users to base all their

desired functionality on ZigBee.

Also, Heile explained, it would be

easier to link two ZigBee networks on

separate floors of a building via a wired

backbone than via a wireless connec-

tion.

ZigBee proponents say widespread

adoption will require consumer aware-

ness. They are, therefore, focusing on

global promotion and marketing such

as worldwide open houses with practi-

cal demonstrations of devices and appli-

cations, Heile noted.

“Research indicates the demand for

having security systems at home will

drive the adoption of ZigBee. The

increasing human dependence on

machines to take control of the house-

hold will also drive the need for ZigBee

in home automation. In fact, by 2006-

07, many homes are expected to have

a minimum of 100 to 150 ZigBee chips

in various appliances,” said Deepa

Doraiswamy, an analyst for Frost &

Sullivan, a market research firm.

According to Chipcon’s Martin,

energy conservation will motivate Zig-

Bee use in Asia and Europe. For exam-

ple, he said, in some countries, running

washing machines at night is either pro-

hibited or incurs higher energy costs.

Owners thus may want to use ZigBee to

run the machines remotely during the

day, when they are not at home.

Stan Bruederle, research vice presi-

dent at Gartner Dataquest, a market

research firm, projects that the number

of devices worldwide connected via

ZigBee will increase from 400,000

this year to 150 million in 2010, as

Figure 2 shows.

nce ZigBee proves itself in its ini-

tial implementation with lighting

and control systems, it will then

play a major role in product tracking,

medical monitoring, and industrial

sensor networks, said Martin.

Eventually, ZigBee could enable sen-

sor networks to undertake such

advanced and promising applications

as checking environmental conditions

in large industrial complexes, tracking

agricultural parameters such as soil

moisture and temperature, overseeing

wastewater processing, and even mon-

itoring a city for bioterror hazards, said

Frost & Sullivan analyst Amit Jain.

The technology has proven to be

sound, many companies have sup-

ported the ZigBee Alliance, and many

people have downloaded the specifica-

tion or bought development kits, so the

issue is when, not if, the technology

will take off, stated Martin.

“The market opportunity for ZigBee

is huge,” said ON World’s Hatler.

“However, in order for it to reach its

full potential, there needs to be more

development and investment in net-

working software, middleware, and

sensor applications.” I

David Geer is a freelance technology

journalist based in Ashtabula, Ohio. Con-

tact him at david@geercom.com.

December 2005

Editor: Lee Garber, Computer,

l.garber@computer.org