ZigBee
Topics Introduction Architecture Node Types Network Topologies Traffic Modes Frame Format Applications Conclusion
Introduction The Wireless technologies (WiFi,GSM,and Bluetooth) All have one thing in common : They send a relatively Large amount of data, at a relatively High data rate. Thus, the devices used in these technologies have high bit rates and consume high power.
But what if we want to send very small data packets using devices that have low data rates and consume very low power? Well, Here comes the role of ZigBee.
What is ZigBee? ZigBee is an established set of specifications built around the IEEE 802.15.4 wireless protocol for wireless personal area networking (WPAN). ZigBee is targeted at radio-frequency (RF) applications that require a low data rate,small packet transmission, long battery life, and secure networking. Specialized in Control and Sensor Networks
Examples for low power /low data rate devices :
Do we really need ZigBee? In other words why do we need a standard to use these devices? Before using ZigBee these low power/low data rate devices were used with no common or shared standard.so, there was no way to form a wireless network between them. ZigBee made it possible for devices from completely different manufactures to communicate and work together.
Now picture a home with entertainment units, security systems including fire alarm, smoke detector and burglar alarm, air-conditioners and kitchen appliances all within whispering distance from each other and imagine a single unit that talks with all the devices, This means that the devices and the control unit would all need a common standard to enable intelligible communication
The Name ZigBee! The name "ZigBee" is derived from the erratic zigging patterns many bees make between flowers when collecting pollen., similar to the way packets would move through a mesh network. ZigBee protocol carries all the benefits of the 802.15.4 protocol with added networking functionality,it was engineered by the ZigBee Alliance, (a group of companies that maintain and publish the ZigBee standard)
ZigBee Alliance - Members and many more...
Architecture
Application Level The Application level contains the applications that run on the network node. These give the device its functionality - essentially an application converts input into digital data, and/or converts digital data into output. A single node may run several applications - for example, an environmental sensor may contain separate applications to measure temperature, humidity and atmospheric pressure.
ZigBee Stack Level The ZigBee Stack level provides the ZigBee functionality, and provides the glue between the applications and the Physical/Data Link level. It consists of stack layers concerned with network structure, routing and security (encryption, key management and authentication).
Physical/Data Link Level The Physical/Data Link level is concerned with low-level network operation such as addressing and message transmission/reception. It is based on the IEEE 802.15.4 standard and comprises the following two layers: MAC (Media Access Control) sub-layer PHY (Physical) layer
Customer API Security 32- / 64- / 128-bit encryption Network Star / Mesh / Cluster-Tree MAC PHY 868MHz / 915MHz / 2.4GHz Silicon Stack App ZigBee Alliance IEEE 802.15.4 the software Network, Security & Application layers Brand management IEEE 802.15.4 the hardware Physical & Media Access Control layers
ZigBee Node Types
ZigBee Node Types 1. ZigBee Coordinator (ZBC) only one in a network initiates network stores information about the network all devices communicate with the ZBC routing functionality bridge to other networks
2. ZigBee Router (ZBR) full function device FFD optional component routes between nodes extends network coverage needs lesser memory than the ZigBee coordinator node can operate in all topologies and can act as a coordinator
3. ZigBee End Device (ZBE) Reduced function device RFD optimized for low power consumption cheapest device type communicates only with the coordinator sensor would be deployed here capable of talking in the network; it cannot relay data from other devices
ZigBee Topologies Using a single PAN coordinator, each node connects directly to the central coordinator all inter-node communications are passed through the coordinator.
In the peer-to-peer topology there is also a PAN coordinator, but it differs from the star topology in that any device can communicate with any other device as long as they are in the range of one another. The peer-to-peer topology allows more complex network formations to be implemented, such as the mesh topology.
A cluster tree network consists of a number of star networks connected whose central nodes are also in direct communications with the single PAN Coordinator.
Using a set of routers and a single PAN coordinator, the network is formed into an interconnected mesh of routers and end nodes which pass information from node to node using the most cost effective path. Should any individual router become inaccessible, alternate routes can be discovered and used providing a robust and reliable network topography.
Network Formation The first FFD that is activated may establish its own network and become a Personal Area Network (PAN) coordinator. Then both FFD and RFD devices can connect to the PAN coordinator. All networks within the radio sphere of influence must have a unique PAN identity. All nodes in a PAN must talk to the PAN Coordinator.
Data Traffic Types 1. Data is periodic. The application dictates the rate, and the sensor activates, checks for data and deactivates. (e.g. sensors) 2. Data is intermittent. The application, or other stimulus, determines the rate, as in the case of say smoke detectors. The device needs to connect to the network only when communication is necessitated. This type enables optimum saving on energy. (e.g. light switch)
Traffic Modes ZigBee employs either of two modes, beacon or nonbeacon to enable the to-and-fro data traffic. Beacon mode is used when the coordinator runs on batteries and thus offers maximum power savings, Non-beacon mode finds favor when the coordinator is mains-powered.
Traffic Modes 1. Beacon mode: beacon send periodically Coordinator and end device can go to sleep between beacons Lowest energy consumption Precise timing needed
When a coordinator wishes to transfer data to a device in a beacon-enabled network, it indicates in the network beacon that the data message is pending. The device periodically listens to the network beacon, and if a message is pending, transmits a MAC command requesting this data, using slotted CSMA-CA. The coordinator optionally acknowledges the successful transmission of this packet. The pending data frame is then sent using slotted CSMA-CA. The device acknowledged the successful reception of the data by transmitting an acknowledgement frame. Upon receiving the acknowledgement, the message is removed from the list of pending messages in the beacon
2. Non-Beacon mode: coordinator/routers have to stay awake (robust power supply needed) asymmetric power
When a coordinator wishes to transfer data to a device in a nonbeacon-enabled network, it stores the data for the appropriate device to make contact and request data. A device may make contact by transmitting a MAC command requesting the data, using unslotted CSMA-CA, to its coordinator at an application-defined rate. The coordinator acknowledges this packet. If data are pending, the coordinator transmits the data frame using unslotted CSMA-CA. If data are not pending, the coordinator transmits a data frame with a zero-length payload to indicate that no data were pending.
Four frame structures : Beacon frame for transmission of beacons Data frame for all data transfers Acknowledgement frame for successful frame receipt confirmations MAC command frame
ZigBee Applications
ZigBee Home Automation Home Entertainment and Control Smart lighting, advanced temperature control, safety and security, movies and music Home Awareness Water sensors, power sensors, smoke and fire detectors, smart appliances and access sensors
Conclusion Why ZigBee? Standards based Low cost Can be used globally Reliable and Supports large number of nodes Easy to deploy Very long battery life Secure