Research and application of Zigbee framework architecture and networking technology

Abstract: Based on the hierarchical network framework architecture of Zigbee network and the protocol stack architecture based on IEEE802.15.4, this paper adopts a method combining theoretical introduction and experimental verification. First, the Zigbee network framework system is introduced. Then, the wireless connection mode and routing selection experiment between wireless control switches and lighting equipment are used to verify the technical characteristics of autonomous search and autonomous networking of Zigbee network. Finally, it is concluded that Zigbee, as a new type of wireless network, has great advantages in wireless IoT sensing and will be more widely used in wireless sensor networks.

In the past few years, with the development of information technology, computers and networks have become part of people's daily lives. Compared with the inconvenience and high fees of wired and long-distance wireless transmission, people have put forward the demand for short-distance communication within a few meters or tens of meters around themselves, and the demand has driven the development of science and technology. So the concept of Wireless Personal Area Network (WPAN) emerged. WPAN network establishes wireless connection for network devices within a short range, connects multiple network devices within a few meters or tens of meters through wireless means, so that they can communicate with each other and even access the local area network (LAN) or the Internet through a certain device. Short-distance and wireless communication technology has become a hot spot for information and communication technology research and development. Various new wireless communication technologies have emerged in an endless stream, and wireless local area networks have gradually entered people's lives. Wireless technologies such as Wi-Fi, Bluetooth (Blue Tooth), WLAN, Zig bee, infrared, etc. have appeared one after another and have gradually become known to people. It is undeniable that various wireless technologies have shown great application potential in the process of marketization, but at the same time, the advantages and disadvantages of various wireless connection methods have also been criticized. Just like the penetration and distance of Wi-Fi, the transmission speed of Bluetooth, the barrier-free and straight-line requirements of infrared. As for the WLAN that is being vigorously promoted by mobile companies and is now in full swing, the small area and high cost of infrastructure deployment have always troubled managers and users. Various wireless network requirements are trying to find a wireless network transmission method that suits them.

With the introduction of the concept of IOT China, the Internet of Things (IoT) has emerged as a new concept in people's vision. The automatic sensing and recognition technology advocated by the IoT has received widespread attention. Wireless communication technology and sensor technology have achieved rapid development. Wireless sensor networks have been more widely used in industrial production, military detection, smart homes, health care, education and scientific research. The demand for wireless data communication in industrial automation and home intelligence is also becoming more and more intense. The wireless requirements of low speed, low power consumption, embeddability and strong network self-healing ability have made Zigbee, which has been unknown in wireless network communication, emerge as a new force and become the main supporting technology for wireless sensor networks.

1 Zigbee framework architecture

Zigbee is composed of the English words "zig" and "bee". Zig means Z-shaped turn, and bee means bee. Together, they represent the figure-eight dance of bees. As we all know, after bees find pollen, they will use a special flying movement language to inform their companions of the location of the newly found pollen. This body language is the Zigbee dance, which is a simple way for bees to convey information. People use Zigbee to name this wireless communication method because Zigbee also has the characteristics of close distance, low complexity, and self-organization like the bee's figure-eight dance.

Zigbee adopts the OSI model architecture, which is composed of modules (entities) called layers. Different modules (entities) are responsible for different functions, and each layer provides data integration and transmission services for the layer above it. Each service module provides a data service interface to its upper layer through the corresponding service access point SAP (Service Access Point, SAP), and each service access point SAP completes the corresponding function through service primitives. The Zigbee protocol stack structure is usually divided into a six-layer structure, as shown in Figure 1:

1) IEEE802.15.4 protocol

Zigbee uses the layered structure of OSI, which can actually be said to be the layered structure of TCP/IP protocol, because it only uses the following two layers, the physical layer (PHY) and the data link layer (DLL). The data link layer is further divided into two sublayers: the media access layer (MAC) and the link layer (LLC). The protocol standards of these two layers are formulated by the IEEE802.15.4 protocol working group, which is why many documents say that Zigbee uses the IEEE802.15.4 protocol.

① Physical layer

The physical layer is the lowest layer of the protocol. It is responsible for exchanging information with the outside world, controlling the operation of the RF transceiver, and defining the interface between the physical layer and the MAC sublayer.

②MAC sublayer

The MAC sublayer is responsible for handling all physical wireless channel access, ensuring that the MAC protocol data unit is correctly sent and received in the physical layer data service, and generating network positioning signals, so MAC is also called the network card address in daily life. In addition, MAC also supports personal area network (PAN) connection and exit, and provides MAC data access links for newly joined PANs. The LLC sublayer provides a data interface for the network layer.

2) Zigbee Alliance Standards

Zigbee Alliance standardized the network layer based on the IEEE802.15.4 protocol and developed a security layer based on the network layer.

① Network layer

The network layer is the core part of the Zigbee protocol stack. Most of the work of the Zigbee Alliance is also reflected in the network layer. The network layer mainly implements functions such as network nodes joining or leaving, route search, and data transmission.

Zigbee's automatic networking and network self-healing functions are also mainly reflected in the network layer. When a network node joins or leaves, Zigbee can automatically recalculate the network and select the most suitable network transmission line. As shown in the figure:

a) Zigbee can automatically search and sense nearby networks to form an interactive network. A network is formed between the desk lamp and the wireless switch.

b) When information needs to be transmitted, it automatically searches for the most suitable network. The top of the table interacts with the switch, automatically monitors, and forms a data interaction link through the thick red line.

c) When one or more of the nodes are turned off, Zigbee automatically reconnects to the network and redefines the line. When the three blue nodes in the figure are turned off, the desk lamp and the wireless switch are redefined and connected. As shown in Figure 4:

② Security layer

The Security Service Provider (SSP) is a functional module independently developed by Zigbee for information security verification. It is not reflected in the OSI and TCP/IP models. It is mainly responsible for implementing key management and key access functions for information exchange.

③Application Programming Interface

The Application Interface (API) is responsible for providing users with a simple application software interface, including Application Sub-layger Suppo rt (APS) and Zigbee Device Object (ZDO), to realize the management of devices at the application layer.

Application Sub-layger Support (APS) provides a link interface between the network layer and the application layer, maintains a link table between the two layers, passes information between the links, and maintains an ASP information base.

The functions of the Zigbee Device Object (ZDO) include the initial application support layer, network layer, and security services. It is responsible for establishing various information required by upper-layer applications, issuing or responding to the link request of the last application, discovering devices and application services on the same network, and establishing security relationships between network devices.

2 Zigbee Networking Research

Zigbee networking generally refers to the construction of a wireless local area network using Zigbee as the main wireless transmission technology. In the process of building a wireless local area network, wireless information receiving and transmitting devices, information modulation and demodulation devices, etc. are generally required.

For the network construction of Zigbee, Zigbee defines two types of network devices: Full Functional Device (FFD) and Reduced Function Device (RFD). The full function device FFD has all the network functions of the MAC layer in the framework structure, that is, it can be used as a device for transmitting and receiving information, and can also be used as a device for modulating and demodulating information; while the reduced function device RFD only provides part of the functions of MAC, that is, it can only transmit and receive information, but cannot modulate and demodulate information. Corresponding to the function, the full function device FFD can be in any position in the network link.

Zigbee defines three topological structures of Zigbee network for the connection mode of each node in the network. It is not difficult to find from the device functions of full-function device FFD and reduced-function device RFD that only full-function device FFD can be used to connect two or more nodes. Therefore, the topological structure of most Zigbee networks is shown in Figure 5.