Seminar Report

ON

ZIGBEE TECHNOLOGY

PREFACE

ZigBee is an open technology developed by the ZigBee Alliance to overcome the limitations of BLUETOOTH and Wi-Fi. ZigBee is an IEEE 802.15.4 standard for data communications with business and consumer devices. It is designed around low-power consumption allowing batteries to essentially last forever. BLUETOOTH as we know was developed to replace wires and Wi-Fi to achieve higher data transfer rate, as such till now nothing has been developed for sensor networking and control machines which require longer battery life and continuous working without human intervention. ZigBee devices allow batteries to last up to years using primary cells (low cost) without any chargers (low cost and easy installation). The ZigBee standard provides network, security, and application support services operating on top of the IEEE 802.15.4 Medium Access Control (MAC) and Physical Layer (PHY) wireless standard. It employs a suite of technologies to enable scalable, selforganizing, self-healing networks that can manage various data traffic patterns. The network layer supports various topologies such star, clustered tree topology and self healing mesh topology which is essential in Smartdust Apart from easy installation and easy implementation. ZigBee has a wide application area such as home networking, industrial networking, Smartdust, many more, having different profiles specified for each field. The upcoming of ZigBee will revolutionize the home networking and rest of the wireless world.

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INDEX 1. Introduction 2. Existing Standards 2.1. Wi-Fi (IEEE standard 802.11) 2.1.1. Standards 2.1.2. Network Types 2.2. Bluetooth (IEEE standard 802.15.1) 2.3. ZigBee (IEEE standard 802.15.4) 2.4. IEEE 802.15.4 2.5. Components of IEEE 802.15.4 2.6. Relation between IEEE 802.15.4 & ZigBee 2.7. ZigBee vs. Bluetooth 2.8. Technology Comparison 3. Introduction to ZigBee 3.1. History 3.2. The ZigBee Alliance 3.3. ZigBee Basics 3.4. The Name ZigBee 3.5. What is ZigBee? 3.6. Why ZigBee? 3.7. Protocol 3.8. OSI overview 3.9. Software and Hardware 3.10. What ZigBee‘s ―Low Power Consumption‖ Means 3.11. ZigBee Benefits 4. ZigBee/IEEE 802.15.4 – General Characteristics 4.1. ZigBee/IEEE 802.15.4 – Typical Traffic Types Addressed 4.2. Transmission Range 4.3. Data Rate 4.4. Data Latency 4.5. Size 4.6. Data security 5. ZigBee/IEEE 802.15.4 WPAN 12 5.1. Components of WPAN 5.2. Network Topology

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6. IEEE 802.15.4 6.1. Received Energy Detection 6.2. Centre Quality Indication 6.3. Clear Channel Assessment 6.4. PPDU Format 7. IEEE 802.15.4 MAC22 7.1. Frame Structure 7.2. Channel Access & Addressing 7.3. Super Frame Structure 7.4. CSMA-CA Algorithm 7.5. Data Transfer Model 7.6. Traffic Type 7.7. MAC Layer Security 8. ZigBee Network Model 9. ZigBee Protocol Stack 9.1. The Physical Layer (PHY) 9.2. Media Access Layer (MAC) 9.2.1. Frame Structure 9.2.2. Super Frame Structure 9.3. Network and Security Layer 9.4. Application Layer 9.4.1. ZigBee Device Object 9.4.2. Application Support Layer 10. ZigBee Routing Mechanism 11. How ZigBee works? 12. ZigBee Security. 13. Licensing 14. ZigBee Applications. 15. ZigBee‘s Future 16. Conclusion 17. Bibliography

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1. Introduction

It was in 1896 that Guglielmo Marconi invented the first wireless telegraph. In 1901 he sent telegraphic signals across the Atlantic ocean from Cornwall to St. John‘s Newfoundland; a distance of 1800 miles. Over the last century, advances in wireless technologies have led to the radio, the television, the mobile telephone, and communication satellites. All type of information can now be send to any corner of the world. A wireless network is a flexible data communication system, which uses wireless media such as radio frequency technology to transmit and receive data over the air, minimizing the need for wired connections. Wireless networks are used to augment rather than replace wired networks and are most commonly used to provide last few stages of connectivity between a mobile user and a wired network. Wireless networks use electromagnetic waves to communicate information from one point to another without relying on any physical connection. Radio waves are often referred to as radio carriers because they simply perform the function of delivering energy to a remote receiver. The data being transmitted is superimposed on the radio carrier so that it can be accurately extracted at the receiving end. Once data is superimposed (modulated) onto the radio carrier, the radio signal occupies more than a single frequency, since the frequency or bit rate of the modulating information adds to the carrier. Multiple radio carriers can exist in the same space at the same time without interfering with each other if the radio waves are transmitted on different radio frequencies. To extract data, a radio receiver tunes in one radio frequency while rejecting all other frequencies. The modulated signal thus received is then demodulated and the data is extracted from the signal. Wireless networks offer the following productivity, convenience, and cost advantages over traditional wired networks: Mobility: provide mobile users with access to real-time information so that they can roam around in the network without getting disconnected from the network. This mobility supports productivity and service opportunities not possible with wired networks. Installation speed and simplicity: installing a wireless system can be fast and easy and can eliminate the need to pull cable through walls and ceilings. Reach of network: the network can be extended to places which cannot be wired. More Flexibility: wireless networks offer more flexibility and adapt easily to changes in the configuration of the network. Reduced cost of ownership: while the initial investment required for wireless network hardware can be higher than the cost of wired network hardware, overall www.seminarreport.net

installation expenses and life-cycle costs can be significantly lower in dynamic environments. Scalability: wireless systems can be configured in a variety of topologies to meet the needs of specific applications and installations. Configurations can be easily changed and range from peer-to-peer networks suitable for a small number of users to large infrastructure networks that enable roaming over a broad area.

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2. EXISTING STANDARDS

In the world of wireless communication there are many standards existing today, each with a specific application field and characteristics which best suites the need. However among so many standard we will only discuss about Wi-Fi, Bluetooth and ZigBee as they are the most complementary standards among all. 2.1. Wi-Fi (IEEE standard 802.11) Wi-Fi is the wireless way to handle networking. It is also known as 802.11 networking and wireless networking. The big advantage of Wi-Fi is its simplicity. Mobile connectivity for computers is a rapidly growing requirement. Of the schemes that are available the IEEE 802.11 standard, often termed Wi-Fi has become the de-facto standard. With peak operating speeds of around 54 Mbps it is able to compete with many wired systems. As a result of the flexibility and performance of the system, many Wi-Fi ―hotpots‖ have been set up and more are following. These enable people to use their laptop computers as they wait in hotels, airport lounges, cafes, and many other places using a wireless link rather that needing to use a cable. 2.1.1.Standards

There is a plethora of standards under the IEEE 802 LMSC (LAN / MAN Standard Committee). Of these even 802.11 has variety of standards, each with a letter suffix. These cover everything from the wireless standards themselves, to standards for security aspects, quality of service and the like: 802.11a – Wireless network bearer operating in the 5 GHz. ISM band with data rate up to 54 Mbps. 802.11b – Wireless network bearer operating in the 2.4 GHz ISM band with data rates up to 11 Mbps 802.11e – Quality of service and prioritization 802.11f – Handover 802.11g – Wireless network bearer operating in 24.GHz ISM band with data rates up to 54 Mbps 802.11h – Power control 802.11i – Authentication and encryption 802.11j – Internetworking 802.11k – Measurement reporting 802.11n – stream multiplexing 802.11s – Mesh networking Of these the standards that are most widely known are the network bearer standards, 802.11a, 802.11b, 802.11g.

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2.1.2.Network types

There are two types of network that can be formed: infrastructure networks; and ad-hoc networks. The infrastructure application is aimed at office areas or to provide a ―hotspot‖. It can be installed instead of a wired system, and can provide considerable cost savings, especially when used in established offices. A backbone wired network is still required and is connected to a server. Wireless network is then split up into a number of cells, each serviced by a base station or Access Point (AP) which acts as a controller for the cell. Each Access Point may have a range of between 30 and 300 metres dependent upon the environment and the location of the Access Point. The other type of network that may be used is termed as Ad-Hoc network. These are formed when a number of computers and peripherals are brought together. They may be needed when several people come together and need to share data or if they need to access a printer without the need for having to use wire connections. In this situation the user4s may only communicate with each other and not a larger wired network. As a result there is no Access Point and special algorithms within the protocols are used to enable one of the peripherals to take over the role of master to control the network with the others acting as slaves. 2.2. Bluetooth Bluetooth is based on IEEE standards 802.15.1. Bluetooth has now established itself in the market place enabling a variety of devices to be connected together using wireless technology. Bluetooth technology has come into its own connecting remote headsets to mobile phones, but it is also used in a huge number of other applications as well. Bluetooth technology originated in 1994 when Erricsson came up with a concept to use a wireless connection to connect items such as an earphone and a cordless headset and the mobile phone. The name of the Bluetooth standard originates from the Danish king Harald Blatand who was king of Denmark between 940 and 981 AD. His name translates as ―Bluetooth‖ and this was used as his nickname. A brave warrior, his main achievement was that of uniting Denmark under the banner of Christianity, and then uniting it with Norway that he had conquered. The Bluetooth standard was named after him because Bluetooth endeavors to unite personal computing and telecommunications devices. Bluetooth is a wireless data system and can carry data at speeds up to 721 Kbps in its basic form and in addition to this it offers up to three voice channels. Bluetooth technology enables a user to replace cables between devices such as printers, fax machines, desktop computers and peripherals, and a host of other digital devices. Furthermore, it can provide a connection between an ad-hoc wireless network and existing wired data networks. The technology is intended to be placed in a low cost module that can be easily incorporated into electronics devices of all sorts. Bluetooth uses the license free Industrial, Scientific and Medical(ISM) frequency band for its radio signals and enables communications to be established between devices up to www.seminarreport.net

a maximum distance of 100 metres. Running in the 2.4 GHz ISM band, Bluetooth employs frequency hopping techniques with the carrier modulated using Gaussian Frequency Shift Keying (GFSK). After a network connection is established between two devices they change their frequency 1600 times per second thus leaving no time for interference, and if by chance there is interference it will be for few microseconds. No other sub network will be working at the frequency at which other sub networks work, thus eliminating interference. 2.3. IEEE 802.15.4 IEEE 802.15 is the working group 15 of the IEEE 802 which specializes in Wireless PAN standards. It includes four task groups (numbered from 1 to 4): Task group 1 (WPAM/Bluetooth) deals with Bluetooth, having produced the 802.15.1 standard, published on June 14, 2002. It includes a medium access control and physical layer specification adapted from Bluetooth 1.1. Task group 2 (coexistence) deals with coexistence of Wireless LAN (802.11) and Wireless PAN. Task group 3 is in fact two groups: 3 (WPAN High Rate) and 3a (WPAN Alternate Higher Rate), both dealing with high-rate WPAN standards (20 Mbit/s or higher). Task group 4 (WPAN Low Rate) deals with low rate but very long battery life (months or even years). The first edition of the 802.15.4 standard was released in May 2003. In March 2004, after forming Task Group 4b, task group 4 put itself in hibernation. The new Task Group 4b aims at clarifying and enhancing specific parts of the Task Group 4 standard. 2.4. Components of IEEE 802.15.4 IEEE 902.15.4 networks use three types of devices. The network coordinator maintains the overall network knowledge. It is the most sophisticated one of the three types and required the most memory and computing power. The Full Function Device (FFD) supports all IEEE 802.15.4 functions and features specified by the standard. It can function as a network coordinator. Additional memory and computing power make it ideal for network router functions or it could be used in network-edge devices (where the network touches the real world).

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The Reduced Function Device (RFD) carries limited (as specified by the standard) functionality to lower cost and complexity. It us generally found in network-edge devices. 2.5. ZigBee` ZigBee is a wireless networking standard that is aimed at remote control and sensor applications which is suitable for operation in harsh radio environments and in isolated locations, It builds on IEEE standard 802.15.4 which defines the physical and MAC layers. Above this ZigBee defines the application and security layer specifications enabling interoperability between products from different manufacturers. In this way ZigBee is a superset of the 802.15.4 specification. With the applications for remote wireless sensing and control growing rapidly it is estimated that the market size could reach hundreds of millions of dollars as early as 2007. This makes ZigBee a very attractive proposition, and one, which warrants the introduction of a focused standard 2.6. Relation between IEEE 802.15.4 & ZigBee

The relationship between IEEE 802.15.4 and ZigBee is similar to that between IEEE 802.11 and the Wi-Fi Alliance. The ZigBee 1.0 specification was ratified on 14 December 2004 and is available to members of the ZigBee Alliance. Most recently, the ZigBee 2007 specification was posted on 30 October 2007. The first ZigBee Application Profile, Home Automation, was announced 2 November 2007. ZigBee operates in the industrial, scientific and medical (ISM) radio bands; 868 MHz in Europe, 915 MHz in the USA and Australia, and 2.4 GHz in most jurisdictions worldwide. The technology is intended to be simpler and less expensive than other WPANs such as Bluetooth. ZigBee chip vendors typically sell integrated radios and microcontrollers with between 60K and 128K flash memory, such as the Jennic JN5148, the Free scale MC13213, the Ember EM250, the Texas Instruments CC2430, the Samsung Electro-Mechanics ZBS240 and the AtmelATmega128RFA1. Radios are also available stand-alone to be used with any processor or microcontroller. Generally, the chip vendors also offer the ZigBee software stack, although independent ones are also available. Because ZigBee can activate (go from sleep to active mode) in 15 msec or less, the latency can be very low and devices can be very responsive — particularly compared to Bluetooth wake-up delays, which are typically around three seconds. Because ZigBees can sleep most of the time, average power consumption can be very low, resulting in long battery life. The first stack release is now called ZigBee 2004. The second stack release is called ZigBee 2006, and mainly replaces the MSG/KVPstructure used in 2004 with a "cluster library". The 2004 stack is now more or less obsolete.

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ZigBee 2007, now the current stack release, contains two stack profiles, stack profile 1 (simply called ZigBee), for home and light commercial use, and stack profile 2 (called ZigBee Pro). ZigBee Pro offers more features, such as multi-casting, many-to-one routing and high security with Symmetric-Key Key Exchange (SKKE), while ZigBee (stack profile 1) offers a smaller footprint in RAM and flash. Both offer full mesh networking and work with all ZigBee application profiles. ZigBee 2007 is fully backward compatible with ZigBee 2006 devices: A ZigBee 2007 device may join and operate on a ZigBee 2006 network and vice versa. Due to differences in routing options, ZigBee Pro devices must become non-routing ZigBee End-Devices (ZEDs) on a ZigBee 2006 or ZigBee 2007 network, the same as ZigBee 2006 or ZigBee 2007 devices must become ZEDs on a ZigBee Pro network. The applications running on those devices work the same, regardless of the stack profile beneath them. 2.7. ZigBee vs. Bluetooth ZigBee looks rather like Bluetooth but is simpler, has a lower data rate and spends most of its time snoozing. This characteristic means that a node on a ZigBee network should be able to run for six months to two years on just two AA batteries. The operational range of ZigBee is 10-75m compared to 10m for Bluetooth (without a power amplifier). ZigBee sits below Bluetooth in terms of data rate. The data rate of ZigBee is 250kbps at 2.4GHz, 40kbps at 915MHz and 20kbps at 868MHz whereas that of Bluetooth is 1Mbps. ZigBee uses a basic master-slave configuration suited to static star networks of many infrequently used devices that talk via small data packets. It allows up to 254 nodes. Bluetooth‘s protocol is more complex since it is geared towards handling voice, images and file transfers in ad hoc networks. Bluetooth devices can support scatter nets of multiple smaller non-synchronized networks (piconets). It only allows up to 8 slave nodes in a basic master-slave piconet set-up. When ZigBee node is powered down, it can wake up and get a packet in around 15msec whereas a Bluetooth device would take around 3sec to wake up and respond. ZigBee and Bluetooth are two solutions for two different application areas. Bluetooth has addressed a voice application by embodying a fast frequency hopping system with a master slave protocol. ZigBee has addressed sensors, controls, and other short message applications by embodying a direct sequence system with a star or peer to peer protocols.

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2.8. Technology Comparisons

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3. ZigBee

The past few years have witnessed a rapid growth of wireless networking. However, up to now wireless networking has been mainly focused on high – speed communications, and relatively long range applications such as IEEE 802.11 wireless local area network standards. The first well known standard focusing on low rate wireless personal area networks was BLUETOOTH. However it has limited capacity for networking of many nodes. There are many wireless monitoring and control applications in industrial and home environments which require longer battery life, lower data rates and less complexity than those from existing standards. For such wireless applications, a new standard called IEEE 802.15.4 has been developed by IEEE. The new standard is also called ZigBee. 3.1. History 

ZigBee-style networks began to be conceived about 1998, when many installers realized that both WiFi and Bluetooth were going to be unsuitable for many applications. In particular, many engineers saw a need for self-organizing ad-hoc digital radio networks.

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The IEEE 802.15.4 standard was completed in May 2003. In the summer of 2003, Philips Semiconductors, a major mesh network supporter, ceased the investment. Philips Lighting has, however, continued Philips' participation, and Philips remains a promoter member on the ZigBee Alliance Board of Directors.

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The ZigBee Alliance announced in October 2004 that the membership had more than doubled in the preceding year and had grown to more than 100 member companies, in 22 countries. By April 2005 membership had grown to more than 150 companies, and by December 2005 membership had passed 200 companies.

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The ZigBee specifications were ratified on 14 December 2004.

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The ZigBee Alliance announces public availability of Specification 1.0 on 13 June 2005, known as ZigBee 2004 Specification.

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The ZigBee Alliance announces the completion and immediate member availability of the enhanced version of the ZigBee Standard in September 2006, known as ZigBee 2006 Specification.

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During the last quarter of 2007, ZigBee PRO, the enhanced ZigBee specification was finalized.

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3.2. The ZigBee Alliance The ZigBee standard is organized under the auspices of the ZigBee Alliance. The ZigBee alliance is an organization of companies working together to define an open global standard for making low power wireless networks. The intended outcome of ZigBee alliance is to create a specification defining how to build different network topologies with data security features and interoperable application profiles. This organization has over 150 members, of which seven have taken on the status of what they term ―promoter.‖ These seven companies are Ember, Honeywell, Invensys, Mitsubishi, Motorola, Philips and Samsung. A big challenge for the alliance is to make the interoperability to work among different products. To solve this problem, the ZigBee Alliance has defines profiles, depending on what type of category the product belongs to. For example there is a profile called home lightning that exactly defines how different brands of home lightning-products should communicate with each other. Under the umbrella of the ZigBee Alliance, the new standard will be pushed forward, taking on board the requirements of the users, manufacturers and the system developers. The Alliance has specified three profiles: Private Profile: In this profile interoperability is not at all important. However producers cannot use the official ZigBee stamp, but can claim that ‗based on ZigBee platform‘. Published Profile: A private profile is shared among other users. Still one cannot use official ZigBee stamp, but can claim ‗based on ZigBee platform‘. Public profile: It is the official ZigBee profile. 3.3. The ZigBee Basics ZigBee is the product of the ZigBee Alliance, an organization of manufacturers dedicated to developing a new networking technology for small, ISM-band radios that could welcome even the simplest industrial and home end devices into wireless connectivity. The ZigBee specification was finalized in December, 2004, and products supporting the ZigBee standard are just now beginning to enter the market. ZigBee is designed as a lowcost, low-power, low-data rate wireless mesh technology. The ZigBee specification identifies three kinds of devices that incorporate ZigBee radios, with all three found in a typical ZigBee network (Figure 1): • a coordinator, which organizes the network and maintains routing tables • routers, which can talk to the coordinator, to other routers, and to reduced function end devices • reduced function end devices, which can talk to routers and the coordinator, but not to each other

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Figure 1: ZigBee networks incorporate coordinators, routers, and reduced function end devices in a variety of topologies (mesh topology shown) To minimize power consumption and promote long battery life in battery-powered devices, end devices can spend most of their time asleep, waking up only when they need to communicate and then going immediately back to sleep. ZigBee envisions that routers and the coordinator will be mains powered and will not go to sleep. To illustrate how these components interrelate, consider ZigBee networking in office lighting. Several manufacturers are currently developing inexpensive sensors for fluorescent tubes that let lights be turned on and off by battery-powered wall switches, with no wires between switch and fixture. The light switch is the end device, powered by a button cell battery that will last for years; the switch wakes up and uses battery power only when flipped on or off to transmit the new state to the fluorescent tubes‘ routers which, as they are already connected to the mains, are not concerned with battery conservation. Any one of the fluorescent tubes can contain the coordinator. The implications are enormous for new office construction – no more electrical runs for lighting, and the ability to reconfigure lighting controls at almost zero cost. ZigBee extends similar benefits to a wide range of industrial automation and control applications. 3.4. The Name ZigBee The name ZigBee is said to come from the domestic honeybee which uses a zig-zag type of dance to communicate important information to other hive members. This communication dance (―The ZigBee Principle‖) is what engineers are trying to emulate with this protocol – a bunch of separate and simple organisms that join together to tackle complex tasks.

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3.5. What is ZigBee? ZigBee is a home-area network designed specifically to replace the proliferation of individual remote controls. ZigBee was created to satisfy the market's need for a costeffective, standards-based wireless network that supports low data rates, low power consumption, security, and reliability The alliance is working closely with the IEEE to ensure an integrated, complete, and interoperable network for the market. The ZigBee Alliance will also serve as the official test and certification group for ZigBee devices. ZigBee is the only standards based technology that addresses the needs of most remote monitoring and control and sensory network applications. The 802.15.4 specification only covers the lower networking layers (MAC and PHY). To achieve inter-operability over a wide range of applications such as Home, Industrial or Building Automation, the higher layers must be standardized as well. The ZigBee Alliance has produced such a standard, using 802.15.4 wireless (generally in the 2.4 GHz band) as the low-level transport. Through the use of 'profiles', the specification may customised to suit various application areas. ZigBee Home Automation Example

It may be helpful to think of IEEE 802.15.4 as the physical radio and ZigBee as the logical network and application software. Following the standard Open Systems Interconnection (OSI) reference model, ZigBee's protocol stack is structured in layers. The first two layers, physical (PHY) and media access (MAC), are defined by the IEEE 802.15.4 standard. The layers above them are defined by the ZigBee Alliance.

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3.6. Why ZigBee? There are a multitude of standards like Bluetooth and Wi-Fi that address mid to heigh data rates for voice, PC LANs, video etc. However, up till now there hasn‘t been a wireless network standard that meets the unique needs of sensors and control devices. Sensors and controls don‘t need high bandwidth but they do need low latency and very low energy consumption for long battery lives and for large device arrays. There are a multitude of proprietary wireless systems manufactured today to solve a multitude of problems that don‘t require high data rates but do require low cost and very low current drain. These proprietary systems were designed because there were no standards that met their application requirements. These legacy systems are creating significant interoperability problems with each other and with newer technologies. The ZigBee Alliance is not pushing a technology; rather it is providing a standardized base set of solutions for sensor and control systems. Here are the following points that justify the use of ZigBee over the existing standards. Low power consumption, simply implemented: Users expect batteries to last many months to years! Consider that a typical single-family house has about 6 smoke/CO detectors. If the batteries for each one only lasted six months, the home owner would be replacing batteries every month! In contrast Bluetooth, which has many different modes and states depending upon your latency and power requirements, ZigBee/IEEE 802.15.4 has two major states: active(transmit/receive) or sleep. The application software needs to focus on the application, not on which power mode is optimum for each aspect of operation. Even mains powered equipment needs to be conscious of energy. ZigBee devices will be more ecological than their predecessors saving megawatts at it full deployment. Consider a future home that has 100 wireless control/sensor devices, Case 1: 802.11 Rx power is 667 mW (always on) @ 100 devices/home & 50,000 homes/city = 150 3.33 megawatts. Case 2: 802.15.4 Rx power is 30 mW (always on) @ 100 devices/home & 50,000 homes/city = 150 kilowatts. Case 3: 802.15.4 power cycled at .1% (typical duty cycle) = 150 watts Low cost to the users means low device cost, low installation cost and low maintenance. ZigBee devices allow batteries to last up to years using primary cells (low cost) without any chargers (low cost and easy installation). ZigBee‘s simplicity allows for inherent configuration and redundancy of network devices provides low maintenance.

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High density of nodes per network: ZigBee‘s use of the IEEE 802.15.4 PHY and MAC allows networks to handle any number of devices. This attribute is critical for massive sensor arrays and control networks. Simple protocol, global implementation: ZigBee‘s protocol code stack is estimated to be about 1/4th of Bluetooth‘s or 802.11‘s. Simplicity is essential to cost, interoperability, and maintenance. The IEEE 802.15.4 PHY adopted by ZigBee has been designed for the 868 MHz band in Europe, the 915 MHz band in N America, Australia, etc; and the 2.4 GHz band is now recognized to be a global band accepted in almost all countries. 3.7. Protocol The protocols build on recent algorithmic research (Ad-hoc On-demand Distance Vector, neuRFon) to automatically construct a low-speed ad-hoc network of nodes. In most large network instances, the network will be a cluster of clusters. It can also form a mesh or a single cluster. The current profiles derived from the ZigBee protocols support beacon and non-beacon enabled networks. In non-beacon-enabled networks (those whose beacon order is 15), an unslotted CSMA/CA channel access mechanism is used. In this type of network, ZigBee Routers typically have their receivers continuously active, requiring a more robust power supply. However, this allows for heterogeneous networks in which some devices receive continuously, while others only transmit when an external stimulus is detected. The typical example of a heterogeneous network is a wireless light switch: The ZigBee node at the lamp may receive constantly, since it is connected to the mains supply, while a battery-powered light switch would remain asleep until the switch is thrown. The switch then wakes up, sends a command to the lamp, receives an acknowledgment, and returns to sleep. In such a network the lamp node will be at least a ZigBee Router, if not the ZigBee Coordinator; the switch node is typically a ZigBee End Device. In beacon-enabled networks, the special network nodes called ZigBee Routers transmit periodic beacons to confirm their presence to other network nodes. Nodes may sleep between beacons, thus lowering their duty cycle and extending their battery life. Beacon intervals may range from 15.36 milliseconds to 15.36 ms * 2 14 = 251.65824 seconds at 250 kbit/s, from 24 milliseconds to 24 ms * 214 = 393.216 seconds at 40 kbit/s and from 48 milliseconds to 48 ms * 214 = 786.432 seconds at 20 kbit/s. However, low duty cycle operation with long beacon intervals requires precise timing, which can conflict with the need for low product cost. In general, the ZigBee protocols minimize the time the radio is on so as to reduce power use. In beaconing networks, nodes only need to be active while a beacon is being transmitted. www.seminarreport.net

In non-beacon-enabled networks, power consumption is decidedly asymmetrical: some devices are always active, while others spend most of their time sleeping. ZigBee devices are required to conform to the IEEE 802.15.4-2003 Low-Rate Wireless Personal Area Network (WPAN) standard. The standard specifies the lower protocol layers—the physical layer (PHY), and the media access control (MAC) portion of the data link layer (DLL). This standard specifies operation in the unlicensed 2.4 GHz (worldwide), 915 MHz (Americas) and 868 MHz (Europe) ISM bands. In the 2.4 GHzband there are 16 ZigBee channels, with each channel requiring 5 MHz of bandwidth. The center frequency for each channel can be calculated as, FC = (2405 + 5 * (ch - 11)) MHz, where ch = 11, 12, ..., 26. The radios use direct-sequence spread spectrum coding, which is managed by the digital stream into the modulator. BPSK is used in the 868 and 915 MHz bands, and OQPSK that transmits two bits per symbol is used in the 2.4 GHz band. The raw, over-the-air data rate is 250 kbit/sper channel in the 2.4 GHz band, 40 kbit/s per channel in the 915 MHz band, and 20 kbit/s in the 868 MHz band. Transmission range is between 10 and 75 meters (33 and 246 feet) and up to 1500 meters for zigbee pro, although it is heavily dependent on the particular environment. The maximum output power of the radios is generally 0 dBm (1 mW). The basic channel access mode is "carrier sense, multiple access/collision avoidance" (CSMA/CA). That is, the nodes talk in the same way that people converse; they briefly check to see that no one is talking before they start. There are three notable exceptions to the use of CSMA. Beacons are sent on a fixed timing schedule, and do not use CSMA. Message acknowledgments also do not use CSMA. Finally, devices in Beacon Oriented networks that have low latency real-time requirements may also use Guaranteed Time Slots (GTS), which by definition do not use CSMA. ZigBee RF4CE On March 3, 2009 the RF4CE (Radio Frequency for Consumer Electronics) Consortium agreed to work with the ZigBee Alliance to jointly deliver a standardized specification for radio frequency-based remote controls. ZigBee RF4CE is designed to be deployed in a wide range of remotely-controlled audio/visual consumer electronics products, such as TVs and set-top boxes. It promises many advantages over existing remote control solutions, including richer communication and increased reliability, enhanced features and flexibility, interoperability, and no line-of-sight barrier.

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3.8. OSI Overview The Open System Interconnection (OSI) reference model, was developed by the International Organization for Standardization (ISO) as a model for the computer protocol architecture, and as a framework for developing protocol standards. The entire point of the model is to separate networking into several distinct functions that operate at di_erent levels. Each layer is responsible for performing a speci_c task or set of tasks, and dealing with the layers above and below it. An illustration of the general OSI-model and where ZigBee is de_ned in the model can be seen in Figure 2.2.

Figure 2.2: OSI model

3.9. Software and hardware The software is designed to be easy to develop on small, inexpensive microprocessors. The radio design used by ZigBee has been carefully optimized for low cost in large scale production. It has few analog stages and uses digital circuits wherever possible. Even though the radios themselves are inexpensive, the ZigBee Qualification Process involves a full validation of the requirements of the physical layer. This amount of

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concern about the Physical Layer has multiple benefits, since all radios derived from that semiconductor mask set would enjoy the same RF characteristics. On the other hand, an uncertified physical layer that malfunctions could cripple the battery lifespan of other devices on a ZigBee network. Where other protocols can mask poor sensitivity or other esoteric problems in a fade compensation response, ZigBee radios have very tight engineering constraints: they are both power and bandwidth constrained. Thus, radios are tested to the ISO 17025 standard with guidance given by Clause 6 of the 802.15.4-2006 Standard. Most vendors plan to integrate the radio and microcontroller onto a single chip. 3.10.

What ZigBee’s “Low Power Consumption” Means

ZigBee‘s low power consumption is rooted not in RF power, but in a sleep modespecifically designed to accommodate battery powered devices. Any ZigBeecompliant radio can switch automatically to sleep mode when it‘s not transmitting, and remain asleep until it needs to communicate again. For radios connected to batterypowered devices, this results in extremely low duty cycles and very low average power consumption. When a radio is in sleep mode, its RF power rating is irrelevant; it‘s only when transmitting that its RF power affects power consumption. In the case of Cirronet‘s ZigBee solutions, a radio with 100 mW RF power will typically consume 150 mA at 3.3V when transmitting, compared to 75 mA at 3.3 V for a radio with 1 mW RF power. The 100 mW radio consumes twice as much power – but only when actively transmitting. As long as the high power radio‘s low noise amplifier is turned off, power consumption while sleeping is roughly equivalent to that of a low power radio. If the high RF power radio is awake and transmitting 5% of the time, which would be a very active radio, the extra average power consumption is roughly 5%. This additional power consumption means that a battery that would last for five years with a 1 mW radio would last four years and nine months with a 100 mW radio. As this illustrates, ZigBee radios with higher RF output ratings are still excellent candidates for use with battery powered devices. It‘s important to note that the ZigBee Alliance doesn‘t itself specify anything for RF power. ZigBee‘s RF power specification comes from IEEE 802.15.4, which specifies a minimum power output rating of 1 mW, with no specified maximum. The de facto 100 mW ―high power‖ level relates to the European limit of 100 mW EIRP, including antenna gain. 3.11.

ZigBee Benefits

In all of its uses, ZigBee offers four inherent characteristics that are highly beneficial: • Low cost The typical ZigBee radio is extremely cost-effective. Chipset prices can be as low as $12 each in quantities as few as 100 pieces (while the 802.15.4 and ZigBee stacks are typically included in this cost, crystals and other discrete components are not). Design-in modules fall in the neighbourhood of $25 in similar quantities. This pricing provides an economic justification for extending wireless networking to even the simplest of devices.

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• Range and obstruction issues avoidance ZigBee routers double as input devices and repeaters to create a form of mesh network. If two network points are unable to communicate as intended, transmission is dynamically routed from the blocked node to a router with a clear path to the data‘s destination. This happens automatically, so that communications continue even when a link fails unexpectedly. The use of low-cost routers can also extend the network‘s effective reach; when the distance between the base station and a remote node exceeds the devices‘ range, an intermediate node or nodes can relay transmission, eliminating the need for separate repeaters (Figure 2).

Figure 2: Heavy lines show a signal from a reduced function end device passing through multiple routers to reach a gateway functioning as a coordinator; lighter lines show possible alternative signal paths • Multi-source products As an open standard, ZigBee provides customers with the ability to choose among vendors. ZigBee Alliance working groups define interoperability profiles to which ZigBee-certified devices must adhere, and certified radio will interoperate with any other ZigBee-certified radio adhering to the same profile, promoting compatibility and the associated competition that allows the end users to choose the best device for each particular network node, regardless of manufacturer. • Low power consumption Basic ZigBee radios operate at 1 mW RF power, and can sleep when not involved in transmission (higher RF power ZigBee radios for applications needing greater range also provide the sleep function). As this makes battery-powered radios more practical than ever, wireless devices are free to be placed without power cable runs in addition to eliminating data cable runs.

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4. ZigBee/IEEE 802.15.4 – General Characteristics         

Data rates of 250 kbps (@2.4 GHz), 40 Kbps (@ 915 MHz) and 20 kbps (@868 MHz) Optimized for low duty-cycle applications (