ZigBee

ZigBee is a little different animal than what we have talked about so far. It covers multiple layers of the protocol stack. It is the network protocol, the transport layer, and an application framework that is the underpinnings of a customer developed application layer.

It has security builtin as a requirement and works using small, low power digital radios. It is a self-organizing wireless mesh-style network. The name comes from the waggle dance honey bees often do on returning to the hive.

The range is short, up to 100 meters line of sight, but it can travel long distances by passing data through a mesh network of other ZigBee devices.

The ZigBee alliance is a consortium of companies that maintain and publish Zigbee standards. ZigBee was first released as a standard in 2003. It is intended to be simpler and cheaper than other wireless protocols. Development code can be as little as 2% of equivalent code on Bluetooth.

Data rates are low and devices tend to be simple. ZigBee standards require at least a two-year battery life for a device to qualify. The data transmission is periodic and intermittent. There are different categories of ZigBee device. A fully functioning device can act as a network coordinator and operates in both star and mesh topologies. A reduced functionality device can only communicate with a network coordinator and works in a star topology.

These devices form a Personal Area Network (PAN). Network interaction times can be very fast. A device can join a network in 30 ms and change from sleeping to active in 15 ms.

There are three types of ZigBee devices in a network:

• A coordinator device that initiates network formation. There is one and only of these for each network. It may also act as a router once the network is formed. It serves as the trust center and is the repository for security keys.
• A router device is optional. It can join with a coordinator or another router device and acts as a multi-hop intermediary in routing of messages.
• An end device has just enough functionality to communicate with its coordinator. It is optional and cannot participate in the routing of messages.

The ZigBee networking routing protocol is reactive. It establishes a route path on demand instead of proactively such as IP. The network protocol used is Ad hoc On-Demand Distant Vector (AODV) which finds a destination by broadcasting to all its neighbors, which then send a requests to all their neighbors, until the destination is found.

The network is silent between connections. Networks are self-healing. ZigBee networks are secured by 128 bit AES encryption. There is often a gateway device that is part of the ZigBee network and also linked to the internet. It translates data into the appropriate format for messaging over the internet. It can also convert ZigBee network routing protocol into IP routing protocol. The gateway is commonly an unconstrained device that does not need to worry much about power.