Abstract:Communication technology is the basis of the Internet of Things. If the Internet of Things is like a logistics system, then communication technology is like a variety of means of transportation for express delivery, such as air, water and land. In the communication technology, generally it can be divided into two categories, one is wireless communication technology, the other is wired communication technology.
This article is shared from Huawei Cloud Community “Things You Didn’t Know About Wired Communication Technology for Internet of Things Communication Technology”. The original author: The Cat Who Love Bread.
The communication technology of the network layer is the medium between the perceptual layer and the platform layer. Communication technology is the basis of the Internet of Things. If the Internet of Things is a logistics system, then communication technology is the equivalent of various means of transportation for express delivery, such as air, water and land. In the communication technology, generally it can be divided into two categories, one is wireless communication technology, the other is wired communication technology. First of all, let’s look at what are the types of wired communication technologies and what are the differences between them?
Ethernet
Ethernet (ETH) is simply the cable network that users use. Ethernet is the main LAN technology of TCP/IP at present, and it is also the most common communication protocol standard of the existing LAN. In the field of the Internet of Things, Ethernet is mainly used in industry except for wired access in the office scene. Because of its low cost and the general standard of IEEE, Ethernet is improved into industrial Ethernet.
The core technology of Ethernet is using CSMA/CD (Carrier Sense Multiple Access/Conflict Detection) communication control mechanism. The CSMA protocol requires the site to listen to the channel before sending data. If the channel is idle, the site can send data; If the channel is busy, the site cannot send data. However, if both sites detect that the channel is idle and start transmitting data at the same time, this will cause a collision almost immediately. In addition, when the station listens to the channel, it hears that the channel is idle, but this does not mean that the channel is really idle, because the data of other stations may be transmitted on the channel at this time, but due to the transmission delay, the signal has not reached the station that is listening to, thus causing the wrong judgment of the channel state. In the early CSMA transmission mode, due to the existence of channel propagation delay, even if the stations of both communication parties did not listen to the carrier signal, there might still be a conflict when sending data. Because they may send data at the same time as they detect that the media is idle, resulting in a collision.
Although CSMA can find conflicts, but it does not have the Prophet conflict detection and prevent functions, resulting in frequent conflicts. Therefore, the CSMA protocol can be further improved to make the sending site continue to listen to the medium in the transmission process to detect whether there is a conflict. If both sites detect that the channel is idle at some point in time and start transmitting data at the same time, they will detect a conflict almost immediately. If a conflict occurs, an electromagnetic wave that exceeds the amplitude of the carrier signal sent by the sending station itself can be detected on the channel, thus determining the existence of a conflict. Once the conflict is detected, the sending site immediately stop sending, and send a bunch of blocking signals on the bus, is used to notify the other site to the bus communication, terminate the damaged frame quickly and can save time and bandwidth requirements site in the process of sending data to carry on the conflict detection, and once detect conflict immediately stop sending data. Such a protocol is known as carrier sense multiple access with collision detection.
RS – 232 and RS – 485
Readers who have studied embedded development may be familiar with RS232. Figure 4-1 shows a schematic interface for RS-232. This interface is familiar to many readers because it exists in the back of a desktop computer. The feature of RS232 is that it mainly supports one-to-one communication and the distance of communication is relatively short, which can only be no more than 20 meters. RS485 is equivalent to an improved version of RS232, to RS485, it supports one-to-many transmission, the bus allows up to 128 transceivers. At the same time, transmission rate and communication distance have been greatly improved.
RS-232 versus RS-485
Table 4-1 shows the differences between RS-232 and RS-485. To put it simply, the differences between the two lie in three points: First, the transmission mode is different. RS-232 adopts unbalanced transmission mode, that is, the so-called single-ended communication. And RS-485 uses balanced transmission, that is, differential transmission mode. The second point is that the transmission distance is different. RS-232 is suitable for the communication between local devices, and the transmission distance is generally no more than 20m. The transmission distance of RS-485 is tens of meters to thousands of meters. The third point is the amount of communication is different, RS232 only allows one-to-one communication, while RS-485 interface on the bus is allowed to connect up to 128 transceivers.
Communication serial bus
In the serial communication, in addition to RS232 and RS485. And USB, also known as Universal Serial Bus, is the serial bus standard that connects computers to other external devices. In USB interface, computer interface in the spring and autumn period and the warring states era, a serial port parallel regime, such as like keyboard, mouse, Modem, printer, scanner, etc should be connected to a different interface, an interface can only connect one device, but the computer can’t support so many interface, so the extension ability is insufficient, and the speed limited. USB is to solve the speed, the ability to expand, easy to use should be born.
Just because it is very common in life, so the Internet of Things, the technology connected with life, will also widely use USB to carry out data transmission. It is important to note that USB is divided into different types according to its interface, among which the four most common ones are Type-A, Type-B, Micro-B and Type-C as shown in Figure 4-2.
M – Bus technology
M-bus, also known as Meterbus. It is a bus specially used for remote meter reading services, such as electricity meter, water meter, gas meter and so on. This technology is not common in domestic meter reading services, but it is widely used in Europe. This bus technology is unique in that it can be used remotely to power the device, and there is no need to lay out a power cord, so if the home power, for the meter is not affected.
Power carrier PLC technology
PLC is also called Powerline Communication. The idea is to transmit data by attaching it to a wire that is normally used. So how it works is you have to load a high-frequency signal with information into an electric current, and then it goes down a wire, and then you have an adapter at the other end that separates the high-frequency signal from the current, and then it’s sent to a computer to communicate with it. But in fact PLC this technology is a disadvantage, it can only be used in the voltage does not change in the near end of the scene. That’s because the technology works by loading high-frequency signals onto a wire, but when the voltage on the wire changes, the high-frequency signals on the wire disappear. Therefore, this technique can only be used in near end scenarios where the voltage does not change. In the meter reading business, PLC technology is mainly used in the meter reading terminal to the management terminal, because when the data is transmitted upward, it will experience the steps of power transformation and transmission, so because the data will disappear after the voltage change, so it can not continue to use PLC technology in the upper layer. Data will be first loaded onto the wire and uploaded to the management terminal, and then the management terminal is connected with the base station, and the data can be uploaded to the database for operation through the switch and server. This is the main process of using PLC power meter reading.
Table 4-2 provides a brief comparison of the above wired communication technologies, among which these technologies are mostly used in industry and public utilities. In the field of the Internet of Things, devices have relatively strong mobility, so there will be less scenarios of wired communication, and more data transmission will be carried out by wireless communication.
The characteristics and application scenarios of four short range wireless communications
Next, we will introduce the common wireless communication technologies of IoT, which can be divided into many different parts, such as cellular network used by operators, and a series of short-range communication technologies such as Bluetooth.
Bluetooth, or Bluetooth
This technology is very common in daily life, Bluetooth in mobile phones, computers, tablets and other devices can be said to have been a necessary technology. Bluetooth technology was first invented by telecommunications giant Ericsson in 1994 as an alternative to the RS232 data line. Bluetooth can connect to multiple devices, overcoming the problem of data synchronization. In the Internet of Things, such as sports bracelets and intelligent electronic scales, Bluetooth technology is needed. The older version of Bluetooth technology, the transmission distance relative to other wireless communication technology is relatively close, only 10 centimeters to 10 meters range. But its transmission rate is relatively fast, up to 1Mbps.
But now Bluetooth technology has developed to Bluetooth version 5.0, although it is still a short range wireless communication technology, but it can be transmitted over a very long distance. Bluetooth 5.0 supports transmission rates up to 3Mbps and distances up to 300 meters. At the same time, Bluetooth technology is divided into two types in the later stage of development, one is BR/DER, and the other is LE. Among them, we need to pay attention to LE type, because LE type Bluetooth technology is very suitable for use in the Internet of Things. Readers may be familiar with Bluetooth technology in the way of peer-to-peer communication, but LE type Bluetooth technology can support a variety of forms of network topology such as peer-to-peer, broadcast and Mesh, which is very suitable for the Internet of Things scenario multi-device connection for data transmission.
Wi-Fi
Most people use Wi-Fi for their daily Internet use, from home to work. So the application of Wi-Fi is very wide. Wi-Fi is typically used in the 2.4G and 5G bands, which allow it to provide different services to different devices. Compared to previous versions of Bluetooth, Wi-Fi can communicate over relatively long distances and supports one-to-many connections. At the same time, its transmission rate is also very fast. But Wi-Fi has obvious drawbacks, starting with poor security and very poor stability. For example, when you’re watching a video, you might find that the video gets stuck halfway through. The other thing is that when the user is playing a computer game, the experience is very obvious. If the user is playing a computer game over Wi-Fi, the latency can vary greatly, sometimes it can be 20 or 30 milliseconds, sometimes it can be 100 or 200 milliseconds. Therefore, the stability of Wi-Fi is relatively poor, and the power consumption of Wi-Fi is relatively high. Like Bluetooth, Wi-Fi has now evolved into the next generation of Wi-Fi6, which supports a transmission rate of 9.6Gbps and a delay of as little as 20ms.
ZigBee
Compared to Wi-Fi and Bluetooth, ZigBee and Z-Wave readers described below may not know much about it. ZigBee is also a wireless technology with short distance and low power consumption. Figure 4-5 is the schematic diagram of the working mode of ZigBee devices. Compared with the schematic diagram of Wi-Fi devices in Figure 4-4, we can actually find the characteristics of this technology. Wi-Fi devices can only connect to an AP or the main concentrator when connected, but ZigBee’s data can also be transferred from device to device. This represents the easy networking characteristics of ZigBee technology. If the intermediate access point of the Wi-Fi device breaks down, the equivalent of the entire network collapses. But ZigBee is different because each device on ZigBee can act as a relay. If one of the devices fails, the other devices can reorganize the network and find another device that can act as a relay and then rebuild the network. ZigBee technology and its name is actually very similar, ZigBee is also called purple bee agreement, because it comes from the eight words dance of bees, as the bees are flying by and “buzz” wings “dance” to transfer pollen location information with his companions, that is to say, the bee constituted groups depend on this way of communication network, This is very similar to the flexible networking features of ZigBee.
In addition, the cost of ZigBee modules is very low, around $2, and its speeds are very low compared to Wi-Fi, ranging from 20 to 250kbps. At the same time, its disadvantages are poor compatibility and difficult maintenance.
Z-Wave
In addition to ZigBee, there is a short-range wireless technology called Z-Wave. Z-Wave is similar to ZigBee, but its difference lies in the fact that Z-Wave is more reliable, but its protocol standards are not open. Meanwhile, Z-Wave’s chips can only be acquired with the company Sigmadesi. Z-Wave technology was originally designed for wireless control of smart homes. Using small data format transmission, 40KB /s transmission rate is enough to handle, early even use 9.6KB /s transmission rate. Compared with other wireless technologies of the same kind, it has a relatively low transmission frequency, a relatively long transmission distance and a certain price advantage.
Comparison of short range wireless technologies
This paper makes a simple comparison of the above four IOT short-range wireless technologies. The main difference lies in the high transmission speed between Bluetooth and Wi-Fi. However, the old version of Bluetooth can only connect one-to-one, while Wi-Fi can connect one-to-many, so Bluetooth is mainly used in mouse, headset, mobile phone and other devices. Wi-Fi, on the other hand, is mostly used for high-speed Internet access in homes and other indoor Settings. At the same time, ZigBee and Z-Wave devices, with their low speed and high number of connections, are unlikely to be used in anything other than the Internet of Things because their transmission rates are too low. So ZigBee and Z-Wave are mainly used in home automation, smart home, smart building and so on.
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