table of Contents
1. Internet of Things Architecture
2. Internet of Things Protocol
Third, the networking method of the Internet of Things
I happened to come into contact with a smart park project. I learned a little bit about things related to the Internet of Things. After reading it for a period of time, I briefly summarized and analyzed what I did not understand clearly.
1. Internet of Things Architecture
The architecture of the Internet of Things is generally divided into a perception layer, a network layer, and an application layer. The perception layer is composed of various sensors and sensor gateways, mainly hardware collecting information; the network layer is composed of various private networks, the Internet, wired or wireless communication networks, etc., mainly using network technology to transmit and process the information obtained by the perception layer; The application layer is the source of business data. The Internet of Things is built on this layer. The data collected by our terminal is connected to the Internet of Things, and then data filtering and data analysis are performed to realize data collection and transmission functions and provide business data.
2. Internet of Things Protocol
The Internet of Things protocol usually has two types of protocols: one is the access protocol and the other is the communication protocol.
1. Access Protocol
The access protocol is generally used for communication between device subnets, and is mainly a perception layer protocol, which does not belong to the TCP/IP protocol stack. This protocol mainly regulates the data format of the information collected by the hardware, and can access the hardware through software. This protocol cannot be directly connected to the Internet of Things. It needs to be converted through the Internet of Things gateway and converted into a communication protocol before it can be connected to the Internet of Things.
Access protocols are divided into short-distance communication protocols, long-distance cellular communication protocols, long-distance non-cellular communication protocols, and wired communication protocols. The specific common protocol classifications are shown in the figure below:
2. Communication protocol
The communication protocol is mainly used to transmit data in the Internet and provide real-time reliable message service for connecting to remote devices. It is a network layer and application layer protocol and belongs to the TCP/IP protocol stack. Common communication protocols include HTTP, CoAP, MQTT, AMGQP, JMS, etc.
If the terminal device supports these communication protocols, it can be directly connected to the Internet of Things. So these communication protocols can be used not only for communication between devices and servers, but also for communication between devices and devices.
Comparing the access protocol and the communication protocol, we can see that if the device supports the access protocol, it also needs to add an IoT gateway to connect to the Internet of Things, and the terminal device that supports the communication protocol can directly connect to the Internet of Things, then why Must there be devices with access protocols? Because some terminal devices do not have an external power supply, they usually rely on button batteries to supply power for about a year, so the power consumption is required to be as low as possible, and the hardware environment required by these communication protocols such as HTTP is difficult to achieve.
Third, the networking method of the Internet of Things
Generally, industrial-grade IoT devices will form subsystems through wired networking or wireless networking, and the system provides the protocols mentioned in the second part of the Internet of Things protocol to connect to the Internet of Things. If the provided protocol is not the TCP/IP protocol stack, it is necessary to perform protocol conversion through the Internet of Things gateway to forward the data to the Internet of Things.
1. Wired networking
(1) Ethernet
Terminal devices are connected to switches, routers, and finally to the Internet using twisted-pair cables or optical fibers. It is the most common networking method. as the picture shows:
（2）RS485
There are two networking modes:
1) The device is directly connected to the host through the RS485 bus, as shown in the figure:
2) The device is connected to the host through the RS485 hub
Application scenarios: access control intercom, building alarm
（3）RS232
1) There is an RS232 serial device directly connected to the host through the RS232 serial port, such as the serial scanner as shown in the figure
2) Connect the RS485 network directly to the host computer through the RS232-RS485 converter, as shown in the figure:
Application scenarios: printers, electrical equipment, etc.
（4）USB
1) The USB interface is directly connected to the host;
2) RS232/RS485 network is converted to USB and connected to the host
For the above wired networking method, except for the first one, it can be connected to the Internet, but the other networking methods transmit data between devices through the bus, and cannot transmit network data, so they cannot be connected to objects. Internet, so you need to add an Internet of Things gateway to transmit network data and forward the data to the Internet of Things. Then the core components of wired networking are terminal equipment, Internet of Things gateway, and Internet of Things. The IoT gateway will be introduced in detail later.
2. Wireless networking
（1）WIFI
1) Small range: one wireless router connects all devices
2) Large range: AC (AC controller) + APs (wireless access points) form a LAN, the device is connected to the AP, the AP is connected to the AC or the device is directly connected to the switch, and the AC is directly connected to the router.
(2) Bluetooth
1) The device can be connected to the Internet through a smart phone or a tablet, and up to 7 can be connected at the same time, as shown in the figure:
2) The device is connected to the Internet through a Bluetooth router, as shown in the figure:
3) The Bluetooth Mesh Ethernet structure forms a self-organizing network, as shown in the figure;
Application scenarios: smart watches, wireless headsets, various wearable devices, etc.; Bluetooth Mesh structure built by indoor lighting nodes
（3）LPWAN
1）NB-IoT
The mobile base station is used for communication, and the base station is connected to the serving gateway. Features: Licensed frequency bands, direct deployment of existing mobile networks, low power consumption, wide range, small amount of transmitted data, and low update frequency.
Application scenarios: street lights, shared bicycles, air detectors, etc.
2）LoRa
Connect to the local area network or the Internet through the LoRa network. Features: Unlicensed frequency band, wide-area private network, up to 2 to 10 kilometers or more.
Application scenarios: smart water meters, smart door locks, parking barriers
（4）ZigBee
Short-distance, low-power, low-speed, and low-cost wireless ad hoc network communication technology. The network composition includes three parts:
ZigBee Coordinate ZC: In a ZigBee network, there is one and only one coordinator. The role is to build and maintain the network; it is the hub of the entire network and the parent node with the highest level;
ZIgBee Router (ZigBee Router ZR): The role is to forward information and assist in coordinating and maintaining the network. It can be both a parent node and a child node;
ZigBee Terminal (ZigBee End-Device ZED): It can only be added to the network and is the most terminal sub-node device. And it can only communicate with the parent node. If communication between two terminals is required, multi-hop or monotonic communication must be carried out through the parent node. It is the largest number of nodes and the only device that allows low power consumption.
There are three network topologies: star network, tree network, and mesh network.
Star network: the simplest one, with a coordinator as the central node, composed of several routers and terminals; the terminal node can only communicate with the central node, if two terminal nodes communicate, it must be forwarded by the central node
Tree network: It can be regarded as composed of multiple star-shaped networks, and each router with nodes can be regarded as the central node of the star-shaped network. The coordinator builds up the entire network, and the router acts as a connection point to spread the network outward in a tree-like manner. Multi-hop communication is formed between nodes through the router in the middle.
Mesh network: In addition to satisfying the tree structure, there is also a communication relationship between neighboring routers.
Generally, ZigBee coordinator and ZigBee router act as IoT gateways to forward data to the Internet of Things, and ZigBee terminal modules are also usually placed in terminal equipment, such as lights, switches, street lights, etc., as shown in the figure:
（5）DAIL
DAIL (Digital Addressable Lighting Interface) is an open standard mainly used in the field of intelligent lighting, which mainly defines the communication methods between devices: such as turning on, off, and adjusting lights.
The network composition mainly includes DAIL bus, DAIL controller. The lighting equipment or switch is connected to the DAIL bus, and then connected to the DAIL controller as a gateway, forming a local area network through RS232/RS485/Ethernet/WIFI/mobile communication.
The DALI bus can connect 64 lighting or switch devices with a length of up to 500 meters. Common networking methods are shown in the figure:
3. Direct device connection
Of course, in addition to the two networking methods mentioned in 1 and 2, if the device supports the communication protocol of the TCP/IP protocol stack, such as HTTP, CoAP, MQTT, XMPP, AMQP, JMS, etc., these devices can support the connection to the Internet of Things. But these devices usually have an external power supply and are not low-power devices. Common devices such as street lights, desktop sharing power banks, etc.
Four, summary
Based on my understanding of some network resources, I briefly summarized some cognitions about the Internet of Things. Later, I will sort out some content of some Internet of Things gateways and Internet of Things protocols. I think it is also some interesting things.