Beginner’s Understanding of ZIGBEE
WIFI and Bluetooth are the most common forms of wireless communication that we use every day but they cannot prove to be an effective option in every case. WIFI consumes a lot of power and therefore is not suggested for battery-operated devices. Bluetooth consumes less power but can only connect to a very limited number.
What if we need a lot of devices connected in a single personal network with low battery consumption such that it consumes less battery? ZIGBEE is the solution here.
ZIGBEE is a short-range wireless communication protocol, built on top of IEEE 802.15.4 international standard developed by Zigbee Alliance. It generally has a low data rate (below 250 kbps) and hence keeping up with the low battery consumption principle. ZIGBEE has a physical range of up to 70 m indoors and 200 m outdoors (although these numbers are often debatable) and hence are suggested for home automation network. In a home automation network various device can be interconnected together such as bulbs, fan and A/C and hence they need a well-optimised network which could connect a lot of devices together with low latency. Such devices do not need to transfer complex messages and hence can function on a low data rate. Home automation is an evolving field of study in IoT and can be studied extensively. ZIGBEE is most commonly used in IoT based projects.
Some Key features of ZIGBEE are:
· ZIGBEE increases system reliability.
· ZIGBEE uses 128-bit AES algorithm to encrypt and authenticate the message signals.
· ZIGBEE network takes up to only ~30 msec to allow a device to join.
· ZIGBEE can support up to 65,000 devices, but that’s only on paper. Practically, it can handle up to 200–300 devices with ease.
· ZIGBEE is an open-source protocol which makes it easy to manufacture and low cost.
· ZIGBEE has frequency bands assigned to it for operation according to different regions in the world.
WORKING OF ZIGBEE DEVICES
Types of Zigbee Devices
1. Coordinators: There is only one coordinator in a network. It is responsible for channel selection, assigns a unique address to each device and assigns an ID to network.
It initiates the transfer of message in a network.
2. Routers: The Intermediate nodes between coordinator and end devices.
It routes traffic between different nodes, receives and store messages which will be transferred to end devices. Gives permission to other devices to join the network.
3. End Devices: It is the receiving end in the network. They can be put on standby and hence low battery consumption. Data has to be passed through the router, as the router wakes up the end devices prior to transferring the message to the end device.
Zigbee Network Topologies
- Star topology:
· Simple and less expensive
· No routers
· If the coordinate fails the whole network fails, range of network limited to a range of the coordinator itself.
2. Mesh topology
· Every node is connected with another node.
· There are different paths between two end devices and data can be re-routed using another path if one fails.
· Recommended for a large number of devices.
3. Tree topology
· It is like a hierarchical system.
· Nodes are not interconnected.
· Gives a wider range of the network.
Channel access
The coordinator assigns only one channel to the network. Hence only a single channel to communicate for all devices.
Two methods for channel access:
1. Contention free method:
- Specific time slot for each device. Known as Guaranteed time slot (GTS).
- Coordinator needs to ensure all devices are in sync. For this, it will release a signal called Beacon. Once the devices receive the beacon, they will sync their clock with the coordinator clock.
- Periodic transmission of data from devices is maintained.
2. Contention based method
- No need for synchronisation.
- If the device wants to transmit the message: it will go into receive mode, detect if there is any signal and transmit the signal if no data is present.
I have tried to summarize the basics for a ZIGBEE protocol so that it will provide the keys to keep in mind while choosing for a wireless network in your next IoT project. Always keep in mind the LOW COST!!
