ZigBee communication protocol

Grzegorz Michalski

We have often written about end devices, such as power plugs or thermostats, in articles about Nexo. They are one of the elements of Nexo architecture – its simplified model we presented in the article “Nexo architecture.” Today, we return to the topic of communication, which we also mentioned in previous publications. Communication is one of the conditions for the smooth functioning of Nexo installations.

ZigBee – what is it needed for?

Nexo is a system that allows you to connect devices from different manufacturers, which is a great convenience for the user. If he buys X-brand thermostats, he can use Y-brand power plugs, and Z-brand motion sensors. For Nexo, this is not a problem if communication between devices is ensured.

So, let’s focus on how our end devices communicate with the Nexo cloud platform. In the previous article about Nexo architecture, we wrote that the Nexo gateway plays a vital role in communication – as an element of the system which keeps end devices connected. It is done thanks to the so-called communication protocol. There are many to choose from, but the most popular among individual users in flats are WiFi, ZigBee, and LoRa/LoRaWAN. This article presents the most essential information about the ZigBee protocol.

What’s ZigBee?

ZigBee is the wireless communication protocol developed in 2002 through the Connectivity Standards Alliance (CSA), formerly ZigBee Alliance. It brings together leading technological companies.1

Due to its numerous advantages, the ZigBee protocol is popular in the Internet of Things (IoT) field. The first version of the protocol was made available in 2004, while version 3.0 has been open since 2016. This protocol is based on the IEEE 802.15.4 standard and, for connecting devices, uses mesh topology.

What are the main advantages of ZigBee?

Reliability, low energy consumption, instant access, and transmission encryption are the most important. Device compatibility helps you create an extended network. Even for many ZigBee devices, the battery can last several years without being replaced because the devices are usually dormant if not in communication mode.

However, this solution can also cause problems.

The main downside is range. Theoretically, the extent of ZigBee devices is 10-100 meters, but because devices are usually installed in buildings, any partitions limit it significantly. The solution to this problem is that ZigBee devices form a mesh network. Each device can communicate with another in such a network, so it is a relatively fault-tolerant network (self-healing). It means that if even one device fails, the network can continue to provide information from the other devices to the end user. This kind of network ensures better coverage and range. This is especially helpful in the case of large-scale buildings.

Types of ZigBee devices

ZigBee devices can be divided into three types – each of them has different functions:

  • Coordinator (Coordinator) – the central unit. Within one ZigBee network, only one such device can operate. The coordinator is the starting node of the network to which other devices can join; they usually have restrictions on the numbers. In the case of Nexo, the coordinator communicates with the Nexo gateway.
  • Router (Router) – this device is functionally similar to classic network range extenders. Its task is to transmit the signal and increase range. Amplifiers can be devices plugged into electricity, e.g., a light bulb, switch, relay, smart socket, or wall switch. The thermostat doesn’t function as a router as it is mainly battery-powered and mostly in sleep mode. The router must be online to fulfill its role.
  • End Device – a battery-operated device, e.g., thermostat, temperature sensor, and window opening sensor. Such a device connects directly to the coordinator or router and forwards information about status and current measures. 

ZigBee architecture within Nexo can be illustrated with the following diagram:

That’s all for today! In the following articles, we will introduce other protocols to make selecting end devices for your Nexo environment easier.

1 https://csa-iot.org/all-solutions/zigbee/