Wi-Fi Alliance. It promised many advantages over existing remote control solutions, including richer communication and increased reliability, enhanced features and flexibility, interoperability, and no line-of-sight barrier. Radio hardware[ edit ] The radio design used by ZigBee has few analog stages and uses digital circuits wherever possible. Products that integrate the radio and microcontroller into a single module are available. All radios derived from the same validated semiconductor mask set would enjoy the same RF characteristics.

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Wi-Fi Alliance. It promised many advantages over existing remote control solutions, including richer communication and increased reliability, enhanced features and flexibility, interoperability, and no line-of-sight barrier. Radio hardware[ edit ] The radio design used by ZigBee has few analog stages and uses digital circuits wherever possible.

Products that integrate the radio and microcontroller into a single module are available. All radios derived from the same validated semiconductor mask set would enjoy the same RF characteristics.

ZigBee radios have very tight constraints on power and bandwidth. An uncertified physical layer that malfunctions can increase the power consumption of other devices on a ZigBee network. Thus, radios are tested with guidance given by Clause 6 of the This standard specifies operation in the unlicensed 2.

Sixteen channels are allocated in the 2. The radios use direct-sequence spread spectrum coding, which is managed by the digital stream into the modulator. The actual data throughput will be less than the maximum specified bit rate due to the packet overhead and processing delays.

For indoor applications at 2. Device types and operating modes[ edit ] ZigBee devices are of three kinds: ZigBee coordinator ZC : The most capable device, the Coordinator forms the root of the network tree and might bridge to other networks. There is precisely one ZigBee coordinator in each network since it is the device that started the network originally the ZigBee LightLink specification also allows operation without a ZigBee coordinator, making it more usable for off-the-shelf home products.

It stores information about the network, including acting as the trust center and repository for security keys. ZigBee end device ZED : Contains just enough functionality to talk to the parent node either the coordinator or a router ; it cannot relay data from other devices. This relationship allows the node to be asleep a significant amount of the time thereby giving long battery life.

The current Zigbee protocols support beacon-enabled and non-beacon-enabled networks. 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 constantly receive, 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 depend on data rate; they may range from 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. In non-beacon-enabled networks, power consumption is decidedly asymmetrical: Some devices are always active while others spend most of their time sleeping.

Except for Smart Energy Profile 2. The standard specifies the lower protocol layers —the physical layer PHY , and the media access control portion of the data link layer DLL. That is, the nodes communicate in a way somewhat analogous to how humans converse: a node briefly checks to see that other nodes are not talking to it, before it starts—but with three notable exceptions.

Beacons are sent on a fixed-timing schedule and do not use CSMA. Message acknowledgments also do not use CSMA. Finally, devices in beacon-enabled networks that have low-latency, real-time requirements may also use guaranteed time slots GTS , which by definition do not use CSMA.

Software[ edit ] The software is designed to be easy to develop on small, inexpensive microprocessors. For more detail, please use one or more of the sources listed in the References section below, or go directly to the ZigBee Alliance web site using the External links provided below.

Network layer[ edit ] The main functions of the network layer are to enable the correct use of the MAC sublayer and provide a suitable interface for use by the next upper layer, namely the application layer. Its capabilities and structure are those typically associated to such network layers, including routing. It deals with network functions such as connecting, disconnecting, and setting up networks.

This layer makes use of star, mesh and tree topologies. It adds an interface to the application layer. On the one hand, the data entity creates and manages network layer data units from the payload of the application-layer and performs routing according to the current topology. On the other hand, there is the layer control, which is used to handle configuration of new devices and establish new networks: it can determine whether a neighboring device belongs to the network and discovers new neighbors and routers.

The control can also detect the presence of a receiver, which allows direct communication and MAC synchronization. The routing protocol used by the network layer is AODV. The neighbors then broadcast the request to their neighbors and onward until the destination is reached.

Once the destination is reached, it sends its route reply via unicast transmission following the lowest cost path back to the source. Once the source receives the reply, it will update its routing table for the destination address of the next hop in the path and the path cost.

Application layer[ edit ] The application layer is the highest-level layer defined by the specification and is the effective interface of the ZigBee system to its end users. It comprises the majority of components added by the ZigBee specification: both ZDO and its management procedures, together with application objects defined by the manufacturer, are considered part of this layer.

This layer binds tables, sends messages between bound devices, manages group addresses, reassembles packets and also transports data. It is responsible for providing service to Zigbee device profiles. Main components[ edit ] The ZDO ZigBee device object , a protocol in the Zigbee protocol stack, is responsible for overall device management, security keys, and policies.

It is responsible for defining the role of a device as either coordinator or end device, as mentioned above, but also for the discovery of new one-hop devices on the network and the identification of their offered services. It may then go on to establish secure links with external devices and reply to binding requests accordingly. The application support sublayer APS is the other main standard component of the layer, and as such it offers a well-defined interface and control services.

It works as a bridge between the network layer and the other elements of the application layer: it keeps up-to-date binding tables in the form of a database, which can be used to find appropriate devices depending on the services that are needed and those the different devices offer. As the union between both specified layers, it also routes messages across the layers of the protocol stack. Communication models[ edit ] ZigBee high-level communication model An application may consist of communicating objects which cooperate to carry out the desired tasks.

The focus of ZigBee is to distribute work among many different devices which reside within individual ZigBee nodes which in turn form a network said work will typically be largely local to each device, for instance, the control of each household appliance. The collection of objects that form the network communicates using the facilities provided by APS, supervised by ZDO interfaces. Within a single device, up to application objects can exist, numbered in the range Two services are available for application objects to use in ZigBee 1.

The message service is designed to offer a general approach to information treatment, avoiding the necessity to adapt application protocols and potential overhead incurred on by KVP.

It allows arbitrary payloads to be transmitted over APS frames. Addressing is also part of the application layer. A network node consists of an The transceiver is the base for addressing, and devices within a node are specified by an endpoint identifier in the range Communication and device discovery[ edit ] For applications to communicate, their comprising devices must use a common application protocol types of messages, formats and so on ; these sets of conventions are grouped in profiles.

Furthermore, binding is decided upon by matching input and output cluster identifiers, unique within the context of a given profile and associated to an incoming or outgoing data flow in a device.

Binding tables contain source and destination pairs. Depending on the available information, device discovery may follow different methods. When the network address is known, the IEEE address can be requested using unicast communication. When it is not, petitions are broadcast the IEEE address being part of the response payload.

End devices will simply respond with the requested address while a network coordinator or a router will also send the addresses of all the devices associated with it. This extended discovery protocol permits external devices to find out about devices in a network and the services that they offer, which endpoints can report when queried by the discovering device which has previously obtained their addresses. Matching services can also be used.

The use of cluster identifiers enforces the binding of complementary entities using the binding tables, which are maintained by ZigBee coordinators, as the table must always be available within a network and coordinators are most likely to have a permanent power supply. Backups, managed by higher-level layers, may be needed by some applications. Binding requires an established communication link; after it exists, whether to add a new node to the network is decided, according to the application and security policies.

Communication can happen right after the association. Direct addressing uses both radio address and endpoint identifier, whereas indirect addressing uses every relevant field address, endpoint, cluster, and attribute and requires that they are sent to the network coordinator, which maintains associations and translates requests for communication.

Indirect addressing is particularly useful to keep some devices very simple and minimize their need for storage. Besides these two methods, broadcast to all endpoints in a device is available, and group addressing is used to communicate with groups of endpoints belonging to a set of devices.

Security services[ edit ] As one of its defining features, Zigbee provides facilities for carrying out secure communications, protecting establishment and transport of cryptographic keys, cyphering frames, and controlling devices.

It builds on the basic security framework defined in IEEE This part of the architecture relies on the correct management of symmetric keys and the correct implementation of methods and security policies.

Basic security model[ edit ] The basic mechanism to ensure confidentiality is the adequate protection of all keying material. Trust must be assumed in the initial installation of the keys, as well as in the processing of security information.

For an implementation to globally work, its general conformance to specified behaviors is assumed. Keys are the cornerstone of the security architecture; as such their protection is of paramount importance, and keys are never supposed to be transported through an insecure channel.

A momentary exception to this rule occurs during the initial phase of the addition to the network of a previously unconfigured device. The ZigBee network model must take particular care of security considerations, as ad hoc networks may be physically accessible to external devices.

Also the state of the working environment cannot be predicted. Within the protocol stack, different network layers are not cryptographically separated, so access policies are needed, and conventional design assumed.

The open trust model within a device allows for key sharing, which notably decreases potential cost.


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