Abstract: Communication technology is the foundation of the Internet of Things. If the Internet of things is compared to the logistics system, then communication technology is equivalent to all kinds of transportation modes of express delivery, such as air transportation, water transportation and land transportation. In communication technology, it can be broadly divided into two categories, one is wireless communication technology, the other is wired communication technology.

This article is shared from huawei Cloud community “Internet of Things Communication Technology wired communication Technology what you don’t know”, the original author: The cat who loves bread.

The communication technology at the network layer is the medium that connects the perception layer and the platform layer. Communication technology is the foundation of the Internet of Things. If the Internet of things is compared to the logistics system, then communication technology is equivalent to the various modes of transportation for express delivery, such as air, water and land transportation. In communication technology, it can be broadly divided into two categories, one is wireless communication technology, the other is wired communication technology. First, let’s look at what types of wired communication technologies are available and what are the differences between them?

Ethernet

Ethernet (ETH) is simply a network cable used by users. Ethernet is the current TCP/IP main LAN technology, but also the current existing LAN using the most common communication protocol standard. In the field of the Internet of Things, Ethernet will be used in addition to the wired access in the office scene, mainly in the industrial application is more, because the cost of Ethernet is low, and is a general standard of IEEE, so it is improved into industrial Ethernet.

The core technology of Ethernet is using CSMA/CD (carrier sense multiple access/collision detection) communication control mechanism. The CSMA protocol requires a 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 almost immediately cause a collision. 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 transmitting on the channel at this time, but due to the propagation delay, the signal has not reached the listening site, thus causing the wrong judgment of the channel status. In the early CSMA transmission mode, due to the existence of channel propagation delay, even if the two sides of the communication site, are not listening to the carrier signal, in the transmission of data may still occur conflict. Because they might send data at the same time when they detect that the medium is idle, causing collisions.

Although CSMA can detect conflicts, it does not have pre-emptive conflict detection and prevention capabilities, resulting in frequent conflicts. Therefore, the CSMA protocol can be further improved, so that the sending site in the transmission process continues to listen to the media, to detect whether there is a conflict. If both sites detect that the channel is idle at some point and start transmitting data at the same time, they will detect a collision almost immediately. If there is a conflict, the electromagnetic wave that exceeds the amplitude of the carrier signal sent by the transmitting site itself can be detected on the channel, so the existence of the conflict can be determined. 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 called carrier sense multiple access with collision detection.

RS – 232 and RS – 485

Readers who have learned embedded development may know more about RS232. Figure 4-1 is the interface diagram of RS-232. Many readers will feel familiar with it, because there is such an interface at the back of a desktop computer. The characteristic of RS232 is that it mainly supports one-to-one communication and the communication distance is relatively short, which can only be no more than 20 meters. RS485 is equivalent to a modified version of RS232, to RS485, it supports one-to-many transmission, the bus allows up to 128 transceivers. At the same time, the transmission rate and communication distance have also 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 rS-232 and RS-485 lie in three points. First, rS-232 adopts unbalanced transmission mode, which is 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 equipment, the transmission distance is generally not more than 20m. The RS-485 has a transmission distance of 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 serial communication, in addition to RS232 and RS485. USB, also known as universal Serial Bus, is a serial bus standard connecting computers and 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 designed to solve the problem of speed, scalability, and ease of use.

Because it is very common in our daily life, the Internet of Things, which is connected with our daily life, will also widely use USB for data transmission. It is important to note that USB is divided into different types according to the interface, among which the four common ones in Figure 4-2 are Type-A, Type-B, micro-B and Type-c.

M – Bus technology

M-bus, also known as MeterBus. It is a special application in the remote meter reading business bus, such as in the electricity meter, water meter, gas meter this meter is used more, this technology is not common in the domestic meter reading business, but is widely used in Europe. What is special about this bus technology is that it can supply power to the device remotely, and it does not need to lay the power cord, so if the power is cut off at home, it will not affect the meter.

Power carrier PLC technology

Table 4-2 is a brief comparison of the above mentioned wired communication technologies, which are mostly used in industry and public utilities. Because in the field of Internet of Things, devices have relatively strong mobility, so wired communication will be used less, and more data will be transmitted through wireless communication.

Four short range wireless communication features and application scenarios

Next, we will introduce the common wireless communication technologies of IoT. Wireless technology can be divided into many different parts, such as cellular networks used by carriers, and a series of short range communication technologies such as Bluetooth.

BluetoothBluetooth

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 developed by telecom giant Ericsson in 1994 as an alternative to RS232 data lines. Bluetooth can connect multiple devices, overcoming the problem of data synchronization. Bluetooth technology is used in the Internet of things, such as sports bands and smart electronic scales. Older versions of Bluetooth were relatively close to other wireless technologies, ranging from 10 centimeters to 10 meters. But its transmission rate is relatively fast, up to 1Mbps.

But now Bluetooth technology has developed to the Version of Bluetooth 5.0, although it is still a short distance wireless communication technology, but its transmission distance has been able to achieve very far. Bluetooth 5.0 supports transmission rates up to 3Mbps and transmission distances up to 300 meters. At the same time, bluetooth technology in the late development is divided into two types of technology, one is BR/DER, 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 for peer-to-peer communication, but LE type Bluetooth technology supports peer-to-peer, broadcast, and Mesh network topologies, making it ideal for data transmission between multiple devices in the Internet of Things scenario.

Wi-Fi

Most people use Wi-Fi for their daily Internet use, from home or at work. So the use of Wi-Fi is very widespread. Wi-fi is typically used on two bands, 2.4g and 5G, which allow it to provide different services to different devices. Compared to previous versions of Bluetooth, Wi-Fi has a relatively long communication distance and supports one-to-many connections. At the same time, the transmission rate is also very fast. However, the disadvantages of Wi-Fi are also very obvious, the first is that it is not safe, very poor stability. For example, when you’re watching a video, you might find that the video gets stuck halfway through. Also, when users are playing computer games, the experience will be very obvious, if you use Wi-Fi to play games, the delay is very large, sometimes it is 20 or 30 milliseconds, sometimes it is 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 is now evolving into the next generation version of Wi-Fi Fi6, which supports transmission rates of 9.6Gbps and latency as low as 20ms.

ZigBee

Readers of ZigBee and the Z-Wave described below may know little about it compared to Wi-Fi and Bluetooth. ZigBee is also a short-range and low-power wireless technology. Figure 4-5 shows the working mode of ZigBee devices. Compared with the working mode of Wi-Fi devices in Figure 4-4, we can actually find the characteristics of this technology. Unlike Wi-Fi devices, which can only connect to the AP or main concentrator, ZigBee data can be transferred between devices. This represents the ZigBee technology is easy to network, if the Wi-Fi device intermediate access point is broken, the equivalent of the entire network will be paralyzed. But ZigBee is different, because each ZigBee device 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 to 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 ZigBee’s flexible networking features.

In addition, the cost of ZigBee modules is very low, around $2, and compared to wi-fi, its speed is very low, only 20 to 250kbps. It also has the disadvantage of being incompatible and difficult to maintain.

Z-Wave

In addition to ZigBee, there is a short-range wireless technology called Z-Wave. Z-wave is similar to ZigBee, but the difference is that Z-Wave is more reliable, but its protocol standards are not open, and Z-Wave chips are only available through SigmaDesigns. Z-wave technology was originally designed for wireless control of smart homes. The transmission rate of 40KB /s is enough to cope with the small data format, and the early transmission rate of 9.6KB /s was even used. Compared with other similar wireless technology, it has a relatively low transmission frequency, a relatively long transmission distance and a certain price advantage.

Short range wireless technology comparison

A simple comparison of the above four IoT short range wireless technologies is made. The main difference is that bluetooth and Wi-Fi have higher transmission speed. However, the old version of Bluetooth can only connect one-to-one, while Wi-Fi can connect one-to-many. Wi-fi, on the other hand, is mainly used for high-speed Internet access in homes and other indoor Settings. At the same time, based on the characteristics of ZigBee and Z-Wave devices with low rate and many connected nodes, it is unlikely to be used in other fields except the Internet of Things, because their transmission rate is too low. So ZigBee and Z-Wave are mainly used in home automation, smart home, smart building and other fields.

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