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Introduction: Communication is extremely common and critical for the Internet of Things (IoT). Whether it is short-range wireless transmission technology or mobile communication technology, both impact the development of IoT. Among these, communication protocols are particularly important as they are the rules and agreements that both parties must follow to complete communication or services.IoT communication protocols can be divided into two main categories:
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One category is access protocols: which are generally responsible for networking and communication between devices within a subnet.
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The other category is communication protocols: which mainly run on traditional Internet TCP/IP protocols, responsible for data exchange and communication between devices over the Internet.
1. Long-Distance Cellular Communication
(1) 2G/3G/4G Communication Protocols, referring to the second, third, and fourth generations of mobile communication system protocols.
(2) NB-IoT
Narrowband Internet of Things (NB-IoT) has become an important branch of the Internet of Everything. NB-IoT is built on cellular networks, consuming about 180kHz of bandwidth, and can be directly deployed on GSM, UMTS, or LTE networks to reduce deployment costs and achieve smooth upgrades. NB-IoT focuses on the low-power wide-area (LPWA) IoT market and is an emerging technology that can be widely applied globally. It features wide coverage, many connections, fast rates, low costs, low power consumption, and excellent architecture.
Application scenarios: The scenarios brought by NB-IoT networks include smart parking, smart firefighting, smart water management, smart street lighting, shared bicycles, and smart home appliances.
(3) 5G
The fifth generation of mobile communication technology, the latest generation of cellular mobile communication technology. The performance goals of 5G are high data rates, reduced latency, energy savings, cost reduction, increased system capacity, and large-scale device connectivity.
Application scenarios: AR/VR, Internet of Vehicles, smart manufacturing, smart energy, wireless medical, wireless home entertainment, connected drones, ultra-high-definition/panoramic live streaming, personal AI assistance, smart cities.
2. Long-Distance Non-Cellular Communication
(1) WiFi
Due to the rapid proliferation of home WiFi routers and smartphones in recent years, the WiFi protocol has also been widely used in the smart home field. The biggest advantage of the WiFi protocol is that it can directly connect to the Internet. Compared to ZigBee, smart home solutions using WiFi protocol eliminate the need for additional gateways, and compared to Bluetooth protocol, they do not rely on mobile terminals like smartphones.
Commercial WiFi coverage in urban public transport, shopping malls, and other public places reveals the potential of commercial WiFi applications.
(2) ZigBee
ZigBee is a low-speed, short-range wireless communication protocol, characterized by high reliability, low speed, low power consumption, low cost, support for a large number of online nodes, various online topologies, low complexity, speed, reliability, and security. ZigBee technology is a new technology that has recently emerged, primarily relying on wireless networks for transmission, enabling short-range wireless connections, and belongs to wireless network communication technology.
The inherent advantages of ZigBee technology have made it a mainstream technology in the IoT industry, with large-scale applications in industrial, agricultural, and smart home fields.
(3) LoRa
LoRa™ (Long Range) is a modulation technology that provides longer communication distances compared to similar technologies. LoRa gateways, smoke detectors, water monitoring, infrared detection, positioning, and power strips are widely used IoT products. As a narrowband wireless technology, LoRa uses time-of-arrival differences to achieve geographic positioning. Application scenarios for LoRa positioning include smart cities and traffic monitoring, metering and logistics, and agricultural positioning monitoring.
3. Short-Distance Communication
(1) RFID
Radio Frequency Identification (RFID) is the abbreviation for Radio Frequency Identification. Its principle is non-contact data communication between a reader and a tag to achieve target identification. RFID has a wide range of applications, including animal chips, car anti-theft chips, access control, parking control, production line automation, and material management. A complete RFID system consists of a reader, electronic tags, and a data management system.
(2) NFC
NFC stands for Near Field Communication technology. NFC is developed based on non-contact radio frequency identification (RFID) technology, combined with wireless interconnection technology, providing a very secure and fast communication method for various electronic products that are becoming increasingly popular in our daily lives. The “near field” in the Chinese name refers to the radio waves of the nearby electromagnetic field.
Application scenarios: Used in access control, attendance, visitor management, conference sign-in, patrolling, etc. NFC has functions such as human-machine interaction and machine-to-machine interaction.
(3) Bluetooth
Bluetooth technology is an open global specification for wireless data and voice communication, based on low-cost short-range wireless connections, establishing a communication environment for fixed and mobile devices. Bluetooth enables wireless information exchange between numerous devices, including mobile phones, PDAs, wireless headsets, laptops, and related peripherals. By utilizing Bluetooth technology, communication between mobile communication terminal devices can be effectively simplified, and communication between devices and the Internet can also be successfully simplified, making data transmission faster and more efficient, thus broadening the path for wireless communication.
4. Wired Communication
(1) USB
USB, short for Universal Serial Bus, is an external bus standard used to specify the connection and communication between computers and external devices. It is an interface technology applied in the PC field.
(2) Serial Communication Protocol
The serial communication protocol specifies the content of data packets, which includes start bits, main data, check bits, and stop bits. Both parties need to agree on a consistent data packet format to send and receive data normally. Common protocols in serial communication include RS-232, RS-422, and RS-485.
Serial communication refers to a communication method where data is transmitted bit by bit between peripherals and computers through data lines. This communication method uses fewer data lines, saving communication costs in long-distance communication, but its transmission speed is lower than parallel transmission. Most computers (excluding laptops) contain two RS-232 serial ports. Serial communication is also a commonly used communication protocol for instruments and equipment.
(3) Ethernet
Ethernet is a local area network technology for computers. The IEEE organization has established the IEEE 802.3 standard, which defines the technical standards for Ethernet, including the physical layer wiring, electronic signals, and media access layer protocols.
(4) MBus
MBus remote meter reading system (symphonic mbus) is a European standard two-wire bus, mainly used for consumption measurement instruments such as heat meters and water meters.
Network Layer and Transport Protocols
1. IPv4
The fourth version of the Internet communication protocol is the fourth revision in the development process of the Internet protocol and the first version of this protocol to be widely deployed. IPv4 is the core of the Internet and the most widely used version of the Internet protocol.
2. IPv6
The sixth version of the Internet protocol, due to the main issue of IPv4 being the limited network address resources, which severely restricts the application and development of the Internet. The use of IPv6 not only solves the problem of the number of network address resources but also addresses the barriers to connecting multiple access devices to the Internet.
3. TCP
Transmission Control Protocol (TCP) is a connection-oriented, reliable, byte-stream-based transport layer communication protocol. TCP is designed to adapt to the layered protocol hierarchy that supports multiple network applications. It provides reliable communication services between paired processes in main computers connected to different but interconnected computer communication networks. TCP assumes it can obtain simple, possibly unreliable datagram services from lower-level protocols.
4. 6LoWPAN
6LoWPAN is a low-power wireless personal area network standard based on IPv6, specifically IPv6 over IEEE 802.15.4.
Application Layer Protocols
1. MQTT Protocol
MQTT (Message Queue Telemetry Transport) is a telemetry transport protocol that primarily provides two messaging modes: publish/subscribe, which is more concise, lightweight, and easy to use, especially suitable for message distribution in constrained environments (low bandwidth, high network latency, unstable network communication), and is a standard transport protocol for the Internet of Things (IoT).
In many cases, including constrained environments such as machine-to-machine (M2M) communication and the Internet of Things (IoT), it has been widely used in satellite link communication sensors, occasionally dial-up medical devices, smart homes, and some miniaturized devices.
2. CoAP Protocol
CoAP (Constrained Application Protocol) is a web-like protocol in the IoT world, suitable for small low-power sensors, switches, valves, and similar components that require remote control or monitoring through standard Internet networks. Servers may not respond to unsupported types.
3. REST/HTTP Protocol
RESTful is a software architectural style based on resources. A resource is an entity on the network or specific information on the network. An image or a song is a resource. RESTful API is an implementation based on the HTTP protocol (HTTP is an application layer protocol characterized by simplicity and speed).
Applications or designs that meet REST specifications are RESTful, and APIs designed according to REST specifications are called RESTful APIs.
4. DDS Protocol
DDS (Data Distribution Service) is a middleware protocol for distributed real-time data distribution service, which is the “TCP/IP” in real-time distributed networks, used to solve the interconnection of network protocols in real-time networks, functioning as a “bus on the bus”.
5. AMQP Protocol
AMQP, or Advanced Message Queuing Protocol, is an application layer standard that provides unified messaging services, an open standard for message-oriented middleware design. Clients based on this protocol can exchange messages with message middleware without being restricted by different products or development languages. Implementations in Erlang include RabbitMQ, among others.
6. XMPP Protocol
XMPP is a protocol based on a subset of standard generalized markup language XML, inheriting the flexibility of development in XML environments. Therefore, applications based on XMPP have strong scalability. After expansion, XMPP can handle user needs by sending extended information and establish applications such as content publishing systems and address-based services on top of XMPP.
Comparison of Some Communication Protocols
1. Comparison of NB-IoT Protocol and LoRa Protocol
First, frequency bands. LoRa operates in unlicensed frequency bands below 1GHz, requiring no additional payment for use, while NB-IoT and cellular communication use licensed frequency bands below 1GHz, which require fees.
Second, battery life. LoRa modules have unique characteristics in handling interference, network overlap, scalability, etc., but cannot provide the same quality of service as cellular protocols. Due to service quality considerations, NB-IoT cannot provide battery life similar to LoRa.
Third, device costs. For terminal nodes, the LoRa protocol is simpler, easier to develop, and has better applicability and compatibility with microprocessors. Additionally, low-cost, relatively mature LoRa modules are already available on the market, with upgraded versions expected to be released continuously.
Fourth, network coverage and deployment timelines. The NB-IoT standard was announced in 2016, and besides network deployment, the corresponding commercialization and establishment of the industrial chain require more time and effort to explore. The entire industrial chain of LoRa is relatively mature, and products are in a “ready to launch” state, with many countries globally conducting or having completed nationwide network deployments.
2. Comparison of Bluetooth, WiFi, and ZigBee Protocols
Currently, WiFi’s advantage is its widespread application, having penetrated thousands of households; ZigBee’s advantage is low power consumption and self-organizing networks; UWB’s advantage is transmission speed; Bluetooth’s advantage is simple networking. However, these three technologies also have their shortcomings, and no single technology can fully meet all the requirements of smart homes.
The emergence of Bluetooth technology has made short-range wireless communication possible, but its complex protocol, high power consumption, and high costs are not suitable for industrial control and home networks that require low costs and low power consumption. Especially, Bluetooth’s biggest obstacle is its limited transmission range, generally effective within about 10 meters, and issues such as weak anti-interference capability and information security are major factors restricting its further development and large-scale application.
WiFi is also a short-range wireless transmission technology that can connect to wireless signals at any time, offering strong mobility, making it suitable for use in office and home environments. However, WiFi also has a fatal flaw. Since WiFi uses radio frequency technology to send and receive data through the air, it is relatively susceptible to external interference.
ZigBee is an internationally accepted wireless communication technology, with each network port capable of connecting up to 65,000 ports, making it suitable for use in homes, industries, agriculture, and other fields, while Bluetooth and WiFi can only connect 10 ports, which clearly cannot meet household needs. ZigBee also has advantages in low power consumption and low cost.
3. Comparison of MQTT Protocol and CoAP Protocol
MQTT is a many-to-many communication protocol used to transmit messages between different clients through an intermediate broker, decoupling producers and consumers by allowing clients to publish and letting the broker decide routing and copy messages. Although MQTT supports some persistence, it is best used as a real-time data communication bus.
CoAP is primarily a point-to-point protocol used to transmit state information between clients and servers. Although it supports observing resources, CoAP is best suited for state transfer models, not entirely event-based.
MQTT clients establish long TCP connections, which usually indicates no issues, while CoAP clients and servers send and receive UDP packets. In NAT environments, tunneling or port forwarding can be used to allow CoAP, or like LWM2M, devices may need to initialize front-end connections first.
MQTT does not provide support for message type tagging or other metadata to help clients understand; MQTT messages can be used for any purpose, but all clients must know the upward data format to allow communication. In contrast, CoAP provides built-in support for content negotiation and discovery, allowing devices to probe each other to find ways to exchange data.
Both protocols have their advantages and disadvantages, and the choice depends on the specific application.
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