ZigBee Technology

Hi this Zigbee is a new technology and some one didn't hear about this. Please go through this article. You will gain some useful information

The low rate (LR) wireless personal access network (WPAN) (IEEE 802.15.4/LRWPAN) is intended to serve a set of industrial, residential, and medical applications with very low power consumption, low cost requirement, and relaxed needs for data rate and QoS .The low data rate enables the LR-WPAN to consume little power. ZigBee technology is a low data rate, low power consumption, low cost, wireless networking protocol targeted toward automation and remote control applications.

The IEEE 802.15.4 committee and ZigBee Alliance worked together and developed the technology commercially known as ZigBee. It is expected to provide low-cost and low-power connectivity for devices that need battery life as long as several months to several years but does not require data transfer rates as high as those enabled by Bluetooth. ZigBee can be implemented in mesh (peer- to-peer) networks larger than is possible with Bluetooth. ZigBee-compliant wireless devices are expected to transmit 10–75 minutes, depending on the RF environment and power output consumption required for a given application, and operate in the unlicensed RF worldwide (2.4 GHz global, 915 MHz America, or 868 MHz Europe) bands. The data rate is 250 kbps at 2.4 GHz, 40 kbps at 915 MHz, and 20 kbps at 868 MHz.

The IEEE 802.15.4 committee is focusing on the specifi cations of the lower two layers of the protocol (the physical and data link layers). On the other hand, ZigBee Alliance aims to provide the upper layers of the protocol stack (from the network to the application layer) for interoperable data interworking, security services, and a range of wireless home and building control solutions. ZigBee Alliance provides interoperability compliance testing, marketing of the standard, and advanced product engineering for the evolution of the standard. This will assure consumers to buy products from different manufacturers with confi dence that those products will work together.

ZigBee often uses a basic master-slave confi guration suited to static star networks of many infrequently used devices that talk via small data packets. It allows up to 254 nodes. Other network topologies such as peer-to-peer and cluster tree are also used. When ZigBee node is powered down, it can wake up and get a packet in around 15 msec.

ZigBee Components and Network Topologies

A ZigBee system consists of several components. The most basic is the device. A devicecan be a full-function device (FFD) or reduced-function device (RFD). A network includes at least one FFD, operating as the personal area network (PAN) coordinator.

The FFD can operate in three modes: a PAN coordinator, a coordinator, or a device. An RFD is intended for applications that are extremely simple and do not need to send large amounts of data. An FFD can talk to reduced-function or full-function devices, while an RFD can only talk to an FFD.

ZigBee supports three types of topologies: star topology, peer-to-peer topology, and cluster tree.

In the star topology, communication is established between devices and a single central controller, called the PAN coordinator. The PAN coordinator may be powered by mains while the devices will most likely be battery powered. Applicationsthat benefi t from this topology are home automation, personal computer (PC) peripherals, toys, and games.

After an FFD is activated for the fi rst time, it may establish its own network and become the PAN coordinator. Each star network chooses a PAN identifier, which is not currently used by any other network within the radio sphere of infl uence.This allows each star network to operate independently.

In the peer-to-peer topology, there is also one PAN coordinator. In contrast to star topology, any device can communicate with any other device as long as they are in range of one another. A peer-to-peer network can be ad hoc, self-organizing, and self-healing. Applications such as industrial control and monitoring, wireless sensor networks and asset and inventory tracking would benefi t from such a topology. It also allows multiple hops to route messages from any device to any other device in the network. It can provide reliability by multipath routing.

The cluster-tree topology is a special case of a peer-to-peer network in which most devices are full-function devices and an RFD may connect to a cluster-tree network as a leaf node at the end of a branch. Any of the full-function devices can act as a coordinator and provide synchronization services to other devices and coordinators. However, only one of these coordinators is the PAN coordinator.

The PAN coordinator forms the first cluster by establishing itself as the cluster head (CLH) with a cluster identifi er (CID) of zero, choosing an unused PAN identifi er, and broadcasting beacon frames to neighboring devices. A candidate device receiving a beacon frame may request to join the network at the cluster head. If the PAN coordinator permits the device to join, it will add this new device to its neighbor list. The newly joined device will add the cluster head as its parent in its neighbor list and begin transmitting periodic beacons such that other candidate devices may then join the network at that device. Once application or network requirements are met, the PAN coordinator may instruct a device to become the cluster head of a new cluster adjacent to the first one. The advantage of the clustered structure is the increased coverage at the cost of increased message latency.

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