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2.2 ZigBee Device Types

A ZigBee network consists of ZigBee nodes (devices). The node architecture is shown in Figure 2.1. A node consists of a microcontroller, a transceiver, and an antenna. A ZigBee node uses stack profiles, which are developed by software. A node can be used for a wide variety of applications—for example, lighting control, smoke-detector, and home-security monitoring. Therefore, a node can support multiple subunits, and each subunit has an application object that describes the subunit function. A node can operate as either a full-function device (FFD) or reduced-function device (RFD). An FFD can perform all the tasks that are defined by the ZigBee standard, and it operates in the full set of the IEEE 802.15.4 MAC layer. An RFD performs only a limited number of tasks.

Figure 2.1

Figure 2.1 Architecture of ZigBee node

  • Coordinator: A coordinator is an FFD and responsible for overall network management. Each network has exactly one coordinator. The coordinator performs the following functions:

    Selects the channel to be used by the network

    Starts the network

    Assigns how addresses are allocated to nodes or routers

    Permits other devices to join or leave the network

    Holds a list of neighbors and routers

    Transfers application packets

  • End device: An end device can be an RFD. An RFD operates within a limited set of the IEEE 802.15.4 MAC layer, enabling it to consume less power. The end device (child) can be connected to a router or coordinator (parent). It also operates at low dutycycle power, meaning it consumes power only while transmitting information. Therefore, ZigBee architecture is designed so that an end device transmission time is short. The end device performs the following functions:

    Joins or leaves a network

    Transfers application packets

  • Router: A router is an FFD. A router is used in tree and mesh topologies to expand network coverage. The function of a router is to find the best route to the destination over which to transfer a message. A router performs all functions similar to a coordinator except the establishing of a network.
  • ZigBee trust center (ZTC): The ZigBee trust center is a device that provides security management, security key distribution, and device authentication.
  • ZigBee gateway: The ZigBee gateway is used to connect the ZigBee network to another network, such as a LAN, by performing protocol conversion.
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