Device Roles：
In an IEEE 802.15.4 network, an FFD device can take three different roles: coordinator,
PAN coordinator, and device. A coordinator is an FFD device that is capable of relaying
messages. If the coordinator is also the principal controller of a personal area network
(PAN), it is called a PAN coordinator . If a device is not acting as a coordinator, it is
simply called a device.
The ZigBee standard uses slightly different terminology (see Figure 1.5 ). A ZigBee
coordinator is an IEEE 802.15.4 PAN coordinator. A ZigBee router is a device that can
act as an IEEE 802.15.4 coordinator. Finally, a ZigBee end device is a device that is
neither a coordinator nor a router. A ZigBee end device has the least memory size and
fewest processing capabilities and features. An end device is normally the least expensive
device in the network.