ZigBee is a specification for the higher protocol layer, and
builds upon the physical (PHY) and medium-access control
(MAC) layers in the 802.15.4 specification [3], Figure
1. Mesh networking topology is supported and routing
is achieved through the ad-hoc on-demand distance vector
(AODV) algorithm. This means that it is the devices
themselves that are responsible for route discovery, and
peer-to-peer communication is possible. In a ZigBee network,
all nodes shares the same channel, and frequency
agility is minimal. There is no frequency hopping, and the
only option is to scan for a channel with the least amount
of interference at startup. There are two classes of network
devices in ZigBee; Full-Function Devices (FFD) and
Reduced-Function Devices (RFD). The former can route
messages in mesh networks and act as the network coordinator,
whereas the latter can only communicate with one
FFD in a star network setup.