ZigBee, also known as ZigBee, is a wireless network protocol for low-speed short-distance transmission. The bottom layer is the media access layer and physical layer using the IEEE 802.15.4 standard specification. The main features are low speed, low power consumption, low cost, support for a large number of online nodes, support for a variety of online topologies, low complexity, fast, reliable and secure.
What is ZigBee Protocol in IoT? Introduction to the ZigBee Standard
1. ZigBee protocol in iot
ZigBee protocol is synonymous with the IEEE 802.15.4 protocol. The technology specified in this agreement is a short-range, low-power wireless communication technology. The name comes from the figure dance of the bee, because the bee (bee) relies on the "dance" of flying and "zig" (zig) flapping its wings to convey the location information of the pollen with its companions, that is to say, the bee relies on this way. constitute the communication network in the group. It is characterized by close proximity, low complexity, low power consumption, low data rate, and low cost. Mainly suitable for automatic control and remote control field, can be embedded in various equipment. In short, ZigBee is a cheap, low-power short-range wireless networking communication technology.
2. ZigBee Standard
The ZigBee Alliance has developed a set of industrial standards for networking and applications on the basis of the IEEE 802.15.4 standard. Unlike the IEEE that only formulates the physical layer (PHY) and media access control sublayer (MAC) underlying standards, the ZigBee Alliance has The network layer, application layer and their supporting sublayers and security sublayers are standardized. Therefore, a complete ZigBee product realized by terminal manufacturers should be composed of high-level application specification, application support sublayer, ZigBee device object (ZDO) sublayer, network layer, MAC and PHY. The network layer and the above standard protocols are formulated by the ZigBee Alliance, and IEEE 802.15.4 is only responsible for the PHY and MAC standards.
The combination of ZigBee standard and IEEE 802.15.4 standard makes its products have the characteristics of low power consumption, easy networking, short-distance interconnection, etc. Therefore, it is considered that its application in sensor network/Internet of Things has considerable advantages. In time, the standards formulated by the ZigBee Alliance cover the seven-layer protocol of the entire Open System Interconnection (OSI), which is very beneficial to the realization of manufacturers. Therefore, ZigBee is considered a mature solution when it comes to sensor network/IoT products and solutions.
2.1 ZigBee Standard Framework
The ZigBee standard adopts a layered and cross-layer design and consists of a series of sublayers and interlayer interfaces. Each layer provides a specific set of services to its upper layer: the data entity provides data transfer services, and the management entity provides all other services. Each service entity provides a service interface to its upper layer through a service access point (SAP). And each SAP provides a series of basic service instructions to complete the corresponding functions. Although it is a standard-based seven-layer open system interconnection model, it only defines those layers that involve ZigBee. The IEEE802.15.4 standard defines the bottom two layers: the physical layer and the media access control sublayer, and the ZigBee Alliance provides the design of the network layer and the application layer (APL) framework. Among them, the application layer framework includes the application support sublayer (APS), the ZigBee device object and the application object formulated by the terminal manufacturer.
Compared to common wireless communication standards, the ZigBee protocol suite is compact and simple, with less specific implementation requirements.
2.2 ZigBee specific standards
In April 2012, the International ZigBee Alliance launched ZigBee Light Link, which means that a common standard has been set, which can effectively solve the above problems. Through the joint development of the world's major lighting equipment manufacturers, ZLL not only defines an advanced light control application information transfer protocol, but also incorporates a simple configuration mechanism, allowing consumers to use it out of the box, and the system configuration is like pressing a button. As easy as pressing a button. In addition to these new features, ZLL has the inherent technical advantages of all ZigBee networks, realizing a low-power, low-cost, robust, and secure wireless network based on IEEE802.15.4.
2.3 Overall features of the ZigBee standard:
2.3.1 Low-cost wireless lighting control solutions in the home field
2.3.2 Simple and intuitive installation without additional tools and expertise
2.3.3 The system is easy to expand and the products are interoperable
2.3.4 Reliable and robust network technology and compatible with other ZigBee standards and devices
2.3.5 Major lighting equipment manufacturers build a global ecosystem to create value for end users
2.3.6 Mature industry chain all over the world - low-cost, high-performance SoC solutions
Certified shelf software solutions:
ZigBee Bulding Automation is the global standard for interoperable products capable of securely monitoring and controlling commercial building systems and is the only BACnet@ approved wireless mesh network for commercial buildings. Products utilizing ZigBee Building Automation enable building owners and operators to control multiple building types (previously inaccessible rooms or disruptive areas) thanks to their low-power wireless operation. Existing wired BACnet building automation systems can now be expanded more easily with lower operating costs.
3. ZigBee wireless data transmission network description
Simply put, ZigBee is a highly reliable wireless data transmission network, similar to CDMA and GSM networks. ZigBee data transmission module is similar to mobile network base station. The communication distance ranges from the standard 75m to several hundred meters and several kilometers, and supports unlimited expansion.
ZigBee is a wireless data transmission network platform composed of up to 65,000 wireless data transmission modules. Within the entire network range, each ZigBee network data transmission module can communicate with each other, and the distance between each network node can be from Standard 75m unlimited expansion.
Different from the CDMA network or GSM network of mobile communication, ZigBee network is mainly established for industrial field automation control data transmission. Therefore, it must be simple, easy to use, reliable and low price. The mobile communication network is mainly established for voice communication. The value of each base station is generally more than one million yuan, while each ZigBee "base station" is less than 1,000 yuan. Each ZigBee network node can not only be used as a monitoring object, for example, the connected sensors can directly collect and monitor data, and can also automatically transfer data from other network nodes. In addition, each ZigBee network node (FFD) can also wirelessly connect with multiple isolated sub-nodes (RFD) that do not undertake the task of network information transfer within the range covered by its own signal.
4. ZigBee's ad hoc network communication method
What is the self-organizing network used by ZigBee technology? A simple example can illustrate this problem. When a team of paratroopers are airborne, each person holds a ZigBee network module terminal. After landing on the ground, as long as they are within the communication range of the network module, they will automatically find each other through each other. An interconnected ZigBee network will soon be formed. Moreover, as people move, their contacts with each other will change. Therefore, the module can also refresh the original network by re-searching for the communication object to determine the connection between them. This is the self-organizing network.
5. Why does ZigBee technology use an ad hoc network to communicate?
Mesh network communication is actually multi-channel communication. In actual industrial sites, due to various reasons, it is often impossible to guarantee that every wireless channel can always be unblocked. There is a temporary interruption of traffic on one road, at which point vehicles (equivalent to our control data) can still reach their destination via other roads since we have multiple lanes. And this is very important for industrial field control.
6. Why do ad hoc networks use dynamic routing?
The so-called dynamic routing means that the data transmission path in the network is not preset, but before data transmission, by searching all the paths available in the network at that time, analyzing their location relationship and distance, and then selecting one of the paths. data transfer. In our network management software, the path selection uses the "gradient method", that is, first select the nearest channel for transmission, if the transmission fails, then use another slightly farther channel for transmission, and so on. until the data reaches its destination. In an actual industrial site, the predetermined transmission path may change at any time, or the path is interrupted for various reasons, or it is too busy for timely transmission. Dynamic routing combined with mesh topology can solve this problem very well, thereby ensuring reliable data transmission.
7. ZigBee's own technical advantages
7.1 Low power consumption
In low-power standby mode, two AA batteries can support one node to work for 6 to 24 months, or even longer. This is the outstanding advantage of ZigBee. In comparison, Bluetooth can work for weeks and WiFi can work for hours.
7.2 Low cost
By greatly simplifying the protocol (less than 1/10 of the bluetooth), the requirements for the communication controller are reduced. According to the prediction analysis, based on the 8051 8-bit microcontroller, the full-function master node needs 32KB code, and the sub-function node is less To 4KB code, and ZigBee protocol royalty-free. The price per chip is about $2.
7.3 Low rate
ZigBee works at a lower rate of 20 to 250 kbps, providing raw data throughput rates of 250 kbps (2.4GHz), 40kbps (915 MHz) and 20kbps (868 MHz), respectively, to meet the application requirements of low-speed data transmission.
7.4 Close range
The transmission range is generally between 10 and 100 m, and can also be increased to 1 to 3 km after increasing the RF transmission power. This refers to the distance between adjacent nodes. If the relay through routing and communication between nodes, the transmission distance will be farther.
7.5 Short delay
ZigBee's response speed is fast, generally only 15ms from sleep to working state, and only 30ms for nodes to connect to the network, which further saves power. In comparison, Bluetooth requires 3 to 10 s, and WiFi requires 3 s.
7.6 High capacity
ZigBee can adopt star, sheet and mesh network structure, and one master node manages several sub-nodes, and one master node can manage 254 sub-nodes at most; at the same time, the master node can also be managed by the upper-layer network node, which can form up to 65,000 sub-nodes. A large network of nodes.
7.7 High security
ZigBee provides a three-level security mode, including no security settings, the use of access control lists (ACL) to prevent unauthorized access to data, and symmetric ciphers using the Advanced Encryption Standard (AES 128) to flexibly determine its security properties.
7.8 License-exempt frequency bands
Using direct sequence spread spectrum in the Industrial Scientific Medical (ISM) bands, 2.4 GHz (global), 915 MHz (US) and 868 MHz (Europe).
ZigBee frequency bands
7.8.1 868MHZ transfer rate is 20KB/S for Europe
7.8.2 915MHZ transfer rate is 40KB/S for the United States
7.8.3 The transfer rate of 2.4GHZ is 250KB/S, which is universal
Since the physical layers of these three frequency bands are not the same, their respective channel bandwidths are also different, which are 0.6MHZ, 2MHZ and 5MHZ respectively. There are 10 and 16 channels respectively.
The spread spectrum and modulation methods of different frequency bands are different. Although the direct spread spectrum (DSSS) method is used, the conversion method from bits to chips is quite different.
The modulation methods all use phase modulation technology, but BPSK is used in the 868MHZ and 915MHZ frequency bands, and OQPSK is used in the 2.4GHZ frequency band. When the transmit power is 0dBm, BLUETOOTH can usually use a range of 10M. The ZigBee based on IEEE 802.15.4 can usually reach a range of 30-50 meters indoors. If there are few obstacles outdoors, it can even reach 100 meters. Action distance. So ZigBee can be classified as a low-speed short-range wireless communication technology.
8. ZigBee performance analysis
8.1 Data rate is relatively low
In the 2.4GHZ frequency band, it is only 250KB/S, and it is only the rate on the link. Excluding the consumption of channel contention response and retransmission, the rate that can really be used by the application may be less than 100KB/S, and the remaining rate may be used by It is divided by multiple applications adjacent to multiple nodes and the same node. Therefore, it is not suitable for things like video.
In terms of reliability, ZigBee has many aspects to ensure. The physical layer adopts spread spectrum technology, which can resist interference to a certain extent. The MAC application layer (APS part) has the function of response retransmission. The CSMA mechanism of the MAC layer enables the node to monitor the channel before sending, which can play a role in avoiding interference. When the ZigBee network is interfered by the outside world and cannot work normally, the entire network can Dynamically switch to another working channel.
Since ZigBee uses random access to the MAC layer and does not support the channel access method of time division multiplexing, it cannot support some real-time services well.
8.4 Energy consumption characteristics
The energy consumption feature is a technical advantage of ZigBee. Usually, the application data rate carried by ZigBee nodes is relatively low. When communication is not required, the node can enter a sleep state with very low power consumption. At this time, the energy consumption may only be in the normal working state. One-thousandth of the time. Because in general, the sleep time accounts for most of the total running time, and sometimes the normal working time is less than one percent, so it achieves a high energy-saving effect.
8.5 Networking and Routing
Network layer features:
8.5.1 Large-scale networking capability of ZigBee: 60,000 nodes per network
8.5.2 bluetooth: 8 nodes per network.
Because the bottom layer of ZigBee adopts the direct expansion technology, if the non-beacon mode is adopted, the network can be expanded greatly, because no synchronization is required and the process of nodes joining and rejoining the network is very fast, generally within 1 second, or even more Fast.bluetooth usually takes 3 seconds.
In terms of routing, ZigBee supports the routing of mesh networks with high reliability, so it can deploy a wide range of networks, and supports multicast and broadcast features, which can bring strong support to rich applications.
9. The application prospect of ZigBee
ZigBee is not used to compete with Bluetooth or other existing standards. It is aimed at specific markets where existing systems cannot meet their needs. It has broad application prospects. The ZigBee Alliance predicts that in the next four to five years, each household will have 50 ZigBee devices, eventually reaching 150 per household. It is estimated that by 2007, the ZigBee market will be worth hundreds of millions of dollars. Its application areas mainly include:
Home and building network: temperature control of air-conditioning system, automatic control of lighting, automatic control of curtains, gas metering control, remote control of household appliances, etc.;
9.1 Industrial control: automatic control of various monitors and sensors;
9.2 Business: smart labels, etc.;
9.3 Public places: smoke detectors, etc.;
9.4 Agricultural control: collect various soil information and climate information;
9.5 Medical: emergency pagers and medical sensors for the elderly and the disabled.
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