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Journal of Theoretical and Applied Information Technology

2005 - 2009 JATIT. All rights reserved.

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THE ROLE OF ZIGBEE TECHNOLOGY IN FUTURE DATACOMMUNICATION SYSTEM

Dr.S.S.Riaz Ahamed.

Professor & Head, Dept of Computer Applications, Mohamed Sathak Engg College,Kilakarai & Principal,Sathak Institute of Technology, Ramanathapuram,TamilNadu, India-623501.

E-mail: [email protected] , [email protected]

ABSTRACT

ZigBee is an IEEE 802.15.4 standard for data communications with business and consumer devices. It isdesigned around low-power consumption allowing batteries to essentially last forever. The ZigBeestandard

provides network, security, and application support services operating on top of the IEEE 802.15.4MediumAccess Control (MAC) and Physical Layer (PHY) wireless standard. It employs a suite of technologies toenable scalable, self-organizing, self-healing networks that can manage various data traffic patterns.ZigBee is a low-cost, low-power, wireless mesh networking standard. The low cost allows the technologyto be widely deployed in wireless control and monitoring applications, the low power-usage allows longerlife with smaller batteries, and the mesh networking provides high reliability and larger range.ZigBee hasbeen developed to meet the growing demand for capable wireless networking between numerous low-power devices. In industry ZigBee is being used for next generation automated manufacturing, with smalltransmitters in every device on the floor, allowing for communication between devices to a centralcomputer. This new level of communication permits finely-tuned remote monitoring and manipulation.

Keywords: Medium Access Control (MAC), Physical Layer (PHY), Wireless Personal Area Networking(WPAN), Open Systems Interconnection (OSI)

1. INTRODUCTION

ZigBee is an established set of specifications forwireless personal area networking (WPAN), i.e.digital radio connections between computers andrelated devices. WPAN Low Rate or ZigBeeprovides specifications for devices that have lowdata rates, consume very low power and are thuscharacterized by long battery life. ZigBee makespossible completely networked homes where alldevices are able to communicate and be controlledby a single unit. The ZigBee Alliance, the standardsbody which defines ZigBee, also publishesapplication profiles that allow multiple OEM

vendors to create interoperable products. Thecurrent list of application profiles either publishedor in the works are:

Home AutomationZigBee Smart EnergyTelecommunication ApplicationsPersonal Home

The relationship between IEEE 802.15.4 andZigBee is similar to that between IEEE 802.11 andthe Wi-Fi Alliance. For non-commercial purposes,the ZigBee specification is available free to thegeneral public. An entry level membership in theZigBee Alliance, called Adopter, costs US$ 3500annually and provides access to the as-yetunpublished specifications and permission to createproducts for market using the specifications.ZigBee is one of the global standards ofcommunication protocol formulated by the relevanttask force under the IEEE 802.15 working group.The fourth in the series, WPAN Low Rate/ZigBeeis the newest and provides specifications for

devices that have low data rates, consume very lowpower and are thus characterized by long batterylife. Other standards like Bluetooth and IrDAaddress high data rate applications such as voice,video and LAN communications.

ZigBee devices are actively limited to a through-rate of 250Kbps, compared to Bluetooth's muchlarger pipeline of 1Mbps, operating on the 2.4 GHz

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ISM band, which is available throughout most ofthe world.In the consumer market ZigBee is beingexplored for everything from linking low-powerhousehold devices such as smoke alarms to acentral housing control unit, to centralized lightcontrols.

The specified maximum range of operation forZigBee devices is 250 feet (76m), substantiallyfurther than that used by Bluetooth capable devices,although security concerns raised over "sniping"Bluetooth devices remotely, may prove to hold truefor ZigBee devices as well. Due to its low poweroutput, ZigBee devices can sustain themselves on asmall battery for many months, or even years,making them ideal for install-and-forget purposes,such as most small household systems. Predictionsof ZigBee installation for the future, most based onthe explosive use of ZigBee in automatedhousehold tasks in China, look to a near futurewhen upwards of sixty ZigBee devices may befound in an average American home, allcommunicating with one another freely andregulating common tasks seamlessly.

The ZigBee Alliance has been set up as anassociation of companies working together toenablereliable,cost-effective,low-power,wirelessly networked, monitoring and controlproducts based on an open global standard. Once amanufacturer enrolls in this Alliance for a fee, hecan have access to the standard and implement it in

his products in the form of ZigBee chipsets thatwould be built into the end devices. Philips,Motorola, Intel, HP are all members of the Alliance. The goal is to provide the consumer withultimate flexibility, mobility, and ease of use bybuilding wireless intelligence and capabilities intoevery day devices. ZigBee technology will beembedded in a wide range of products andapplications across consumer, commercial,industrial and government markets worldwide. Forthe first time, companies will have a standards-based wireless platform optimized for the uniqueneeds of remote monitoring and controlapplications, including simplicity, reliability, low-cost and low-power.

The target networks encompass a wide range ofdevices with low data rates in the Industrial,Scientific and Medical (ISM) radio bands, withbuilding-automation controls like intruder/firealarms, thermostats and remote (wireless) switches,video/audio remote controls likely to be the mostpopular applications. So far sensor and control

devices have been marketed as proprietary items forwant of a standard. With acceptance andimplementation of ZigBee, interoperability will beenabled in multi-purpose, self-organizing meshnetworks

2. ZIGBEE CHARACTERISTICS

The focus of network applications under the IEEE802.15.4 / ZigBee standard include the features oflow power consumption, needed for only two majormodes (Tx/Rx or Sleep), high density of nodes pernetwork, low costs and simple implementation.

These features are enabled by the followingcharacteristics,

2.4GHz and 868/915 MHz dual PHY modes. Thisrepresents three license-free bands: 2.4-2.4835GHz, 868-870 MHz and 902-928 MHz. Thenumber of channels allotted to each frequency bandis fixed at sixteen (numbered 11-26), one(numbered 0) and ten (numbered 1-10)respectively. The higher frequency band isapplicable worldwide, and the lower band in theareas of North America, Europe, Australia and NewZealand .

Low power consumption, with battery liferanging from months to years. Considering thenumber of devices with remotes in use at present, it

is easy to see that more numbers of batteries needto be provisioned every so often, entailing regular(as well as timely), recurring expenditure. In theZigBee standard, longer battery life is achievableby either of two means: continuous networkconnection and slow but sure battery drain, orintermittent connection and even slower batterydrain.

Maximum data rates allowed for each of thesefrequency bands are fixed as 250 kbps @2.4 GHz,40 kbps @ 915 MHz, and 20 kbps @868 MHz.

High throughput and low latency for low duty-cycle applications (

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50m typical range

Fully reliable hand-shaked data transferprotocol.

Different topologies as illustrated below: star,peer-to-peer, mesh

periodically, locks on and looks for messagesaddressed to it. If message transmission iscomplete, the coordinator dictates a schedule forthe next beacon so that the device goes to sleep'; infact, the coordinator itself switches to sleep mode.

While using the beacon mode, all the devices in amesh network know when to communicate witheach other. In this mode, necessarily, the timingcircuits have to be quite accurate, or wake upsooner to be sure not to miss the beacon. This inturn means an increase in power consumption bythe coordinator's receiver, entailing an optimalincrease in costs.

Figure 1: ZigBee Topologies

3. TRAFFIC TYPES

ZigBee/IEEE 802.15.4 addresses three typicaltraffic types. IEEE 802.15.4 MAC canaccommodate all the types.

1. Data is periodic. The application dictates the

rate, and the sensor activates, checks for data anddeactivates.

2. Data is intermittent. The application, or otherstimulus, determines the rate, as in the case of saysmoke detectors. The device needs to connect to thenetwork only when communication is necessitated.This type enables optimum saving on energy.

3. Data is repetitive, and the rate is fixed a priori.Depending on allotted time slots, called GTS(guaranteed time slot), devices operate for fixeddurations.

ZigBee employs either of two modes, beacon ornon-beacon to enable the to-and-fro data traffic.Beacon mode is used when the coordinator runs onbatteries and thus offers maximum power savings,whereas the non-beacon mode finds favour whenthe coordinator is mains-powered.

In the beacon mode, a device watches out for thecoordinator's beacon that gets transmitted at

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Figure 2: Beacon Network Communication[Source:www.zigbee.org/en/resources]

The non-beacon mode will be included in a systemwhere devices are asleep' nearly always, as insmoke detectors and burglar alarms. The deviceswake up and confirm their continued presence inthe network at random intervals.

On detection of activity, the sensors spring toattention', as it were, and transmit to the ever-waiting coordinator's receiver (since it is mains-powered). However, there is the remotest ofchances that a sensor finds the channel busy, inwhich case the receiver unfortunately would miss acall'.

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It may be helpful to think of IEEE 802.15.4 as thephysical radio and ZigBee as the logical networkand application software. Following the standardOpen Systems Interconnection (OSI) referencemodel, ZigBee's protocol stack is structured inlayers. The first two layers, physical (PHY) and

media access (MAC), are defined by the IEEE802.15.4 standard. The layers above them aredefined by the ZigBee Alliance. The IEEE workinggroup passed the first draft of PHY and MAC in2003.

Figure 3: Non-Beacon Network Communication[Source:www.zigbee.org/en/resources]

4. ARCHITECTURE

ZigBee is a home-area network designed

specifically to replace the proliferation ofindividual remote controls. ZigBee was created tosatisfy the market's need for a cost-effective,standards-based wireless network that supports lowdata rates, low power consumption, security, andreliability. To address this need, the ZigBeeAlliance,anindustryworkinggroup(www.zigbee.org), is developing standardizedapplication software on top of the IEEE 802.15.4wireless standard. The alliance is working closelywith the IEEE to ensure an integrated, complete,and interoperable network for the market. Forexample, the working group will provideinteroperability certification testing of 802.15.4systems that include the ZigBee software layer.

The ZigBee Alliance will also serve as the officialtest and certification group for ZigBee devices.ZigBee is the only standards-based technology thataddresses the needs of most remote monitoring andcontrol and sensory network applications.

ZigBee-compliant products operate in unlicensedbands worldwide, including 2.4GHz (global), 902to 928MHz (Americas), and 868MHz (Europe).Raw data throughput rates of 250Kbps can beachieved at 2.4GHz (16 channels), 40Kbps at915MHz (10 channels), and 20Kbps at 868MHz (1channel). The transmission distance is expected to

range from 10 to 75m, depending on power outputand environmental characteristics. Like Wi-Fi,Zigbee uses direct-sequence spread spectrum in the2.4GHz band, with offset-quadrature phase-shiftkeying modulation. Channel width is 2MHz with5MHz channel spacing. The 868 and 900MHzbands also use direct-sequence spread spectrum butwith binary-phase-shift keying modulation.

5. FRAME STRUCTURE

Figure 5 illustrates the four basic frame types

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

Figure 4: ZigBee stack architecture

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Figure5: The four basic frame types defined in802.15.4: Data, ACK, MAC command, and beacon

The data frame provides a payload of up to 104bytes. The frame is numbered to ensure that all

packets are tracked. A frame-check sequenceensures that packets are received without error.This frame structure improves reliability in difficultconditions.

Another important structure for 802.15.4 is theacknowledgment (ACK) frame. It provides feedbackfrom the receiver to the sender confirming that thepacket was received without error. The device takesadvantage of specified "quiet time" between framesto send a short packet immediately after the data-packet transmission.

A MAC command frame provides the mechanismfor remote control and configuration of clientnodes. A centralized network manager uses MACto configure individual clients' command frames nomatter how large the network.

Finally, the beacon frame wakes up client devices,which listen for their address and go back to sleepif they don't receive it. Beacons are important formesh and cluster-tree networks to keep all thenodes synchronized without requiring those nodesto consume precious battery energy by listening forlong periods of time.

6. CHANNEL ACCESS, ADDRESSING

Two channel-access mechanisms are implementedin 802.15.4. For a non"beacon network, a standardALOHA CSMA-CA (carrier-sense medium-accesswith collision avoidance) communicates withpositive acknowledgement for successfullyreceived packets. In a beacon-enabled network, asuperframe structure is used to control channelaccess. The superframe is set up by the networkcoordinator to transmit beacons at predeterminedintervals (multiples of 15.38ms, up to 252s) andprovides 16 equal-width time slots between

beacons for contention-free channel access in eachtime slot. The structure guarantees dedicatedbandwidth and low latency. Channel access in eachtime slot is contention-based. However, thenetwork coordinator can dedicate up to sevenguaranteed time slots per beacon interval for qualityof service.

Device addresses employ 64-bit IEEE and optional16-bit short addressing. The address field within theMAC can contain both source and destinationaddress information (needed for peer-to-peeroperation). This dual address information is used inmesh networks to prevent a single point of failure

within the network.

7. DEVICE TYPES

These devices have 64-bit IEEE addresses, withoption to enable shorter addresses to reduce packetsize, and work in either of two addressing modes star and peer-to-peer.

ZigBee networks use three device types:

The network coordinator maintains overallnetwork knowledge. It's the mostsophisticated of the three types andrequires the most memory and computingpower.The full function device (FFD) supports all802.15.4 functions and features specifiedby the standard. It can function as anetwork coordinator. Additional memoryand computing power make it ideal fornetwork router functions or it could beused in network-edge devices (where thenetwork touches the real world).The reduced function device (RFD) carrieslimited (as specified by the standard)functionality to lower cost and complexity.It's generally found in network-edgedevices.

8. SECURITY

Security and data integrity are key benefits of theZigBee technology. ZigBee leverages the securitymodel of the IEEE 802.15.4 MAC sublayer whichspecifies four security services:

access controlthe device maintains a listof trusted devices within the networkdata encryption, which uses symmetric key128-bit advanced encryption standardframe integrity to protect data from beingmodified by parties without cryptographickeyssequential freshness to reject data framesthat have been replayedthe networkcontroller compares the freshness valuewith the last known value from the device

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and rejects it if the freshness value has notbeen updated to a new value

The actual security implementation is specified bythe implementer using a standardized toolbox ofZigBee security software.

The following table-1 shows the Wireless technology comparison chart,

Standard Bandwidth

Wi-Fi

PowerConsumption

ProtocolStack Size

Stronghold

High data rate

Applications

Internetbrowsing,PC networking, filetransfers

WirelessUSB,handset, headset

Upto 400+mATX, 100+KB54Mbpsstandby 20mA

40mATX, ~100+KBstandby 0.2mA

30mAstandby

3#&956;A

TX, 4"32KB

Bluetooth 1Mbps

ZigBee 250kbps

Interoperability,cable replacement

Long battery life, Remotecontrol,low costbattery-operated

products, sensors

Table 1 Wireless technology comparison chart

9. CONLUSIONIt is likely that ZigBee will increasingly play animportant role in the future of computer andcommunication technology. In terms of protocolstack size, ZigBee's 32 KB is about one-third ofthe stack size necessary in other wirelesstechnologies (for limited capability end devices,

the stack size is as low as 4 KB). The IEEE802.15.4based ZigBee is designed for remotecontrols and sensors, which are very many innumber, but need only small data packets and,mainly, extremely low power consumption for(long) life. Therefore they are naturally different intheir approach to their respective applicationarenas. The ZigBee Alliance targets applications"across consumer, commercial, industrial andgovernment markets worldwide". Unwiredapplications are highly sought after in manynetworks that are characterized by numerous nodesconsuming minimum power and enjoying longbattery lives. ZigBee technology is designed tobest suit these applications, for the reason that it

enables reduced costs of development and veryfast market adoption.

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