ZigBee technology and different types of network topologies that are supported in Zigbee

1. Zigbee Technology:

i. The IEEE 802.15.4 committee and zigbee alliance worked together and developed the technology commercially known as zigbee.

ii. Zigbee technology is a low data rate, low power consumption, low cost, wireless networking protocol targeted towards automation and remote control application.

iii. 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

iv. Zigbee technology operates in unlicensed RF worldwide (2.4 GHZ global, 915 MHz America, or 868 MHz Europe) bands.

v. The data rate is 250 kbps at 2.4 GHz, 40kbps at 915 MHz, and 20 kbps at 868 MHz.

vi. Depending on RF environment and power output consumption required for a given application, Zigbee compliant devices are expected to transmit 10-75 minutes.

vii. Zigbee network configurations can be larger than possible with Bluetooth. There can be up to 254 nodes. viii. When zigbee node is powered down, it can wake up and get a packet in around 15 msec.

ix. The IEEE 802.15.4 committee focuses on specifications of lower two layers of protocol (physical and data link) while zigbee Alliance focuses on upper layers of protocol stack (from network to application layer).

x. ZigbeeAlliance provides inter operable data networking, security services, interoperability compliance testing, and a range of wireless home and building control solutions.

xi. Thus customers can buy products from different manufacturers with confidence that those products will work together.

xii. The marketing of standard, advanced product engineering helps in the evolution of zigbee standard.

2. ZigbeeTopologies:

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

i. Types of device:

• A zigbee system consists of several components. The most basic is the device.
• A device can be a full-functional device (FFD) or reduced-function device (RFD).
• An FFD can talk to an RFD or an FFD while an RFD can only talk to an FFD.
• The FFD can operate in three modes: a PAN coordinator, a coordinator, or a device.
• A network must include at least one FFD, operating as the ‘personal Area Network (PAN) coordinator’.

ii. Star Topology:

• In the star topology, communication is established between devices and a single central controller, called the PAN coordinator.
• After an FFD is activated for first time, it may establish its own network and become PAN coordinator.
• Each star network chooses a PAN identifier, which is not currently used by any other network within the radio sphere of influence. This allows each star network to operate independently.
• The PAN coordinator may be powered by mains while the devices will most likely be battery powered.
• Applications that benefit from this topology are home automation, personal computer (PC) peripherals, toys and games.

iii. Peer-to-peer topology:

• In peer-to-peer topology too, there is one PAN coordinator.
• Any device can communicate with any other device as long as they are in range of one another.
• Thus a peer-to-peer network can be ad hoc (unfixed), self-organizing, and self-healing.
• Peer-to-peer topology allows multiple hops to route messages from any device to any other device in the network. It can provide reliability by multipath routing.
• Applications such as industrial control and monitoring, wireless sensor networks and assets and inventory tracking would benefit from such a topology.

iv. Cluster-tree topology:

• The cluster-tree topology is a special case of a peer-to-peer network in which most devices are FFDs.
• Any of the FFDs can act as a coordinator and provide synchronization services to other devices and coordinators. However, only one of these coordinators is PAN coordinator.
• The PAN coordinator forms the first cluster by establishing itself as cluster head (CLH) with a cluster identifier of zero (CID), choosing an unused PAN identifier.
• The CLH broadcasts beacon frames to neighboring devices.
• A candidate device receiving a beacon frame may request to join the network at 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.
• In this way, an RFD may connect to a cluster tree network as a leaf node at the end of a branch.
• The advantage of the clustered structure is increased coverage at the cost of increased message latency.

Features :
1. ZigBee- wireless devices are expected to transmit 10–75 minutes, depending on the RF environment and power output.
2. operate in the unlicensed Frequency band of 2.4 GHz globally.
3. The data rate is 250 kbps at 2.4 GHz ( low data rate).
4. ZigBee supports three types of topologies: star topology, peer-to-peer topology, and cluster tree.
5. It allows up to 254 nodes with a master in a network.
6. Uses IEEE 802.15.4 standard.

Applications :
1. Sensing and location determination at disaster sites.
2. Automotive sensing, such as pressure , temperature monitoring etc
3. In agriculture such as the sensing of soil moisture, pesticide, herbicide, and pH levels.
4. In home automation and networking including heating, ventilation, air conditioning, security, and lighting.
5. In health monitoring systems.