| What is ZigBee? |
| What is IEEE802.15.4? |
| How is ZigBee different from other wireless standards(e.g.Bluetooth)? |
| What are the real-lift applications of ZigBee? |
| How reliable is the data delivery? |
| How long is the battery life? |
| How long is the Transmission Range? |
| What is the Data Latency for ZigBee Networks? |
| How large/small a ZigBee Network can be? |
| What types of ZigBee Devices exist in a network? |
| What Topologies are supported by ZigBee? |
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| What is ZigBee? |
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ZigBee is an open WPAN ( Wireless Personal Area Networks ) standard based on the IEEE 802.15.4 protocol. While IEEE 802.15.4 defines PHY ( physical ) and MAC ( medium access ) layers, ZigBee takes care of higher layers ( e.g., network, application profiles, …) The development of ZigBee/IEEE 802.15.4 is motivated to address those applications in which only low transfer data rate is involved. Compared to other wireless communication techniques, ZigBee/IEEE 802.15.4 possesses the following advantages:
• Low power consumption;
• Low cost;
• Flexible reliable, and self-healing network;
• Large number of nodes;
• Fast, easy deployment;
• Security;
• Ability to be used globally;
• Product interoperability;
• Vendor independence.
The term “ZigBee” originates from honeybees', a method of communicating newfound food sources. This silent-but-powerful communication system is known as the “ZigBee Principle.” By dancing in a zig-zag pattern, the bee is able to share critical information, such as the location, distance, and direction of a newly discovered food source to its fellow hive members.
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| What is IEEE802.15.4? |
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IEEE 802.15.4 is a standard defined by the IEEE ( Institute of Electrical and Electronics Engineers, Inc.) for low-rate WPAN. This standard defines the ”physical layer” and the “medium access layer.” The specification for the physical layer, or PHY, defines a low-power spread spectrum radio operating a t 2.4 GHz with a basic bit rate of 250 kilobits per second. There are also PHY specifications for 915 MHz and 868 MHz that operate at lower data rates. For more information about IEEE 802.14.5 please refer to the official page at http://www.ieee802.org/15/pub/TG4.html.
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| How is ZigBee different from other wireless standards(e.g.Bluetooth)? |
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There is a multitude of standards that address mid to high data rates for voice, PC LANs, video, etc. However, until ZigBee here hasn't been a wireless network standard that meets the unique needs of sensors and control devices. Sensors and control devices 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.
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| What are the real-lift applications of ZigBee? |
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ZigBee is well suited for a wide range of building automation, industrial, medical and residential control and monitoring applications. Examples include the following:
• Lighting controls;
• Automatic Meter Reading;
• Wireless smoke and CO detectors;
• HVAC control;
• Heating control;
• Home control, including units such as intrusion sensors, motion detectors, glass break detectors, standing water sensors, loud sound detectors, etc;
• Environmental controls;
• Blind, drapery and shade controls;
• Medical sensing and monitoring;
• Universal Remote Control to a Set-Top Box which includes Home Control;
• Industrial and building automation;
• Asset management.
E.g., wireless sensors ( temperature, humidity, shock, etc.) are installed into containers, where they form a mesh network. Multiple containers in a ship form a mesh to report sensor data to the ship control center, and further to a port control center.
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| How reliable is the data delivery? |
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Reliable data delivery is critical to ZigBee applications. The underlying IEEE 802.15.4 standard provides strong reliability through several mechanisms at multiple layers. For example, it uses 27 channels in three separate frequency bands.
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| How long is the battery life? |
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The basic IEEE 802.15.4 node is fundamentally efficient in erms of battery performance. You can expect battery lifetimes from a few months to many years as a result of a host of system's power-saving modes and battery-optimized network parameters, such as a selection of beacon intervals, guaranteed time slots, and enablement/disablement options. Consider a typical security application, such as a magnetic reed switch door sensor. The sensor itself consumes almost no electricity; it's the radio that uses the bulk of the power. The sensor is configured to have a “heartbeat” at one-minute intervals and to immediately send a message when an event occurs. Assuming dozens of events per day, analysis shows that the sensor can still outlast an alkaline AAA battery. The configuration allows the network to update the sensor parameters remotely, change its reporting interval, or perform other remote functions and still have (theoretical) battery longevity well beyond the shelf life.
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| How long is the Transmission Range? |
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The IEEE 802.15.4 standard specifies transmitter output power at a nominal -3dBm (0.5 mW), with the upper limit controlled by the local regulatory agencies. At -3 dBm output, single-hop ranges of 10 to more than 100m are reasonable, depending on the environment, antenna, and aperating frequency band. By introducing extensible and sophisticated network fuction, ZigBee allows multi-hop and flexible routing, providing communication ranges exceeding the basic single-hop.
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| What is the Data Latency for ZigBee Networks? |
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ZigBee/IEEE 802.15.4 can provide latencies as low as 16ms in a beacon-centric network, using guaranteed time slots to prevent interference from other sensors. Data latency will affect battery life. Generally, if you relax data-latency requirements, you can assume that the battery life of the client nodes will increase.
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| How large/small a ZigBee Network can be? |
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The addressing space allows of extreme node density—up to 264 devices ( 64 bit IEEE address ), which may form different topologies depending on customer needs: star, mesh, cluster tree. At the same time, using local addressing, simple networks of more than 65,000 (2^16) nodes can be configured, with reduced address overhead.
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| What types of ZigBee Devices exist in a network? |
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According to IEEE MAC specification that introduces three device types, ZigBee specifies the following ZigBee Devices:
• ZigBee Coordinator ( MAC Network Coordinator ). Maintains overall network knowledge; most sophisticated of the three types; most memory and computing power
• ZigBee Router (MAC Full Function Device: Carries full IEEE 802.15.4 functionality and all features specified by the standard).
• ZigBee End Device ( MAC Reduced Function Device: Carriers limited functionality to control cost and complexity. Also, may be MAC Full Function Device ). That's where the physical devices reside.
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| What Topologies are supported by ZigBee? |
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The figure below illustrates the possible network configurations and the roles of the devices.
As shown above, there are three different network topologies that are supported by Zigbee, namely the star, mesh and cluster tree or hybrid networks. Each has its own advantages and can be used to advantage in different situations. The star network is commonly used, having the advantage of simplicity. As the name suggests it is formed in a star configuration with outlying nodes communicating with a central node. Mesh or peer-to-peer networks enable high degrees of reliability. They consist of a variety of nodes placed as needed, and nodes within range being able to communicate with each other to form a mesh. Messages may be routed across the network using the different stations as relays. There is usually a choice of routes that can be used and this makes the network very robust. If interference is present on one section of a network, then another can be used instead. Finally there is what is known as a cluster tree network. This is essentially a combination of star and mesh topologies.
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