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2.6 ZigBee Protocol Architecture

Figure 2.6 shows the ZigBee protocol architecture. The ZigBee Alliance developed the ZigBee device object (ZDO), the application support sublayer (APS), the network layer, and security management. IEEE 802.15.4 is used for the MAC layer and physical layer.

Figure 2.6

Figure 2.6 ZigBee protocol architecture

The ZigBee protocol architecture is divided into three sections, as follows:

  • IEEE 802.15.4, which consists of the MAC and physical layers.
  • ZigBee layers, which consist of the network layer, the ZigBee device object (ZDO), the application sublayer, and security management.
  • Manufacturer application: Manufacturers of ZigBee devices can use the ZigBee application profile or develop their own application profile.

2.6.1 Physical Layer

The physical layer performs modulation on outgoing signals and demodulation on incoming signals. It transmits information and receives information from a source. Table 2.2 shows the physical layer frequency band, data rate, and channel numbers.

Table 2.2. Physical Layer Frequency Band

Frequency Band

Country

Data Rate

Channel Numbers

868.3MHz

European countries

20Kbps

0

902–928 MHz

United States

40Kbps

1–10

2.405GHz

Worldwide

250Kbps

11–26

2.6.2 Media Access Control (MAC) Layer

The functions of the MAC layer are to access the network by using carrier-sense multiple access with collision avoidance (CSMA/CA), to transmit beacon frames for synchronization, and to provide reliable transmission.

2.6.3 Network Layer

The network layer is located between the MAC layer and application support sublayer. It provides the following functions:

  • Starting a network
  • Managing end devices joining or leaving a network
  • Route discovery
  • Neighbor discovery

2.6.4 Application Support Sublayer (APS)

The application support sublayer (APS) provides the services necessary for application objects (endpoints) and the ZigBee device object (ZDO) to interface with the network layer for data and management services. Some of the services provided by the APS to the application objects for data transfer are request, confirm, and response. Furthermore, the APS provides communication for applications by defining a unified communication structure (for example, a profile, cluster, or endpoint).

  • Application object (endpoint): An application object defines input and output to the APS. For example, a switch that controls a light is the input from the application object, and the output is the light bulb condition. Each node can have 240 separate application objects. An application object may also be referred to as an endpoint (EP). Figure 2.7 shows an example of home control lighting.
    Figure 2.7

    Figure 2.7 Home control lighting

  • ZigBee device object (ZDO): A ZigBee device object performs control and management of application objects. The ZDO performs the overall device management tasks:

    Determines the type of device in a network (for example, end device, router, or coordinator)

    Initializes the APS, network layer, and security service provider

    Performs device and service discovery

    Initializes coordinator for establishing a network

    Security management

    Network management

    Binding management

  • End node: Each end node or end device can have multiple EPs. Each EP contains an application profile, such as home automation, and can be used to control multiple devices or a single device. More to the point, each EP defines the communication functions within a device. As shown in Figure 2.7, the bedroom switch controls the bedroom light, and the remote control is used to control three lights: bedroom, hallway1, and hallway2.
  • ZigBee addressing mode: ZigBee uses direct, group, and broadcast addressing for transmission of information. In direct addressing, two devices communicate directly with each other. This requires that the source device has both the address and endpoint of the destination device. Group addressing requires that the application assign a group membership to one or more devices. A packet is then transmitted to the group address in which the destination device lies. The broadcast address is used to send a packet to all devices in the network.
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