A Complete Summary of IoT Communication Protocols

With the continuous increase in the number of IoT devices, communication or connectivity between these devices has become an important consideration. Communication is essential for the development of the IoT, whether it is short-range wireless transmission technology or mobile communication technology. In communication, communication protocols are particularly important as they define the rules and agreements that entities must follow to complete communication or provide services.

This article introduces several available IoT communication protocols, each with different performance, data rates, coverage ranges, power requirements, and memory usage. Each protocol has its own advantages and, to some extent, disadvantages. Some communication protocols are only suitable for small household appliances, while others can be used for large-scale smart city projects. IoT communication protocols can be divided into two main categories:

• Access protocols: Typically responsible for networking and communication between devices within a subnet.

• Communication protocols: Mainly run on top of the traditional Internet TCP/IP protocol and are responsible for data exchange and communication between devices over the Internet.

A. Physical Layer and Data Link Layer Protocols

1. Long-Range Cellular Communication

(i) 2G/3G/4G Communication Protocols: Referring to the second, third, and fourth-generation mobile communication system protocols.

(ii) NB-IoT (Narrowband Internet of Things): NB-IoT is an important branch of the Internet of Things network. It is built on cellular networks and consumes only about 180kHz of bandwidth. It can be deployed directly 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 has the characteristics of wide coverage, multiple connections, fast data rates, low cost, low power consumption, and excellent architecture.

Application scenarios: NB-IoT network enables applications such as smart parking, smart firefighting, smart water management, smart streetlights, bike sharing, and smart home appliances.

(iii) 5G: The fifth-generation mobile communication technology is the latest generation of cellular mobile communication technology. 5G aims to achieve high data rates, reduced latency, energy savings, cost reduction, increased system capacity, and massive device connectivity.

Application scenarios: AR/VR, connected vehicles, smart manufacturing, smart energy, wireless healthcare, wireless home entertainment, connected drones, ultra-high-definition/panoramic live streaming, personal AI assistants, smart cities.

2. Long-Range Non-Cellular Communication

(i) WiFi: Due to the rapid popularity 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 WiFi protocol is direct access to the Internet. Compared to ZigBee, WiFi-based smart home solutions eliminate the need for additional gateways, and compared to Bluetooth protocols, they eliminate the dependence on mobile terminals such as smartphones.

The commercial deployment of WiFi in public places such as urban public transportation and shopping malls demonstrates the potential of WiFi in public coverage.

(ii) ZigBee: ZigBee is a low-speed short-range wireless communication protocol, which is a reliable wireless data transmission network. Its main features include low speed, low power consumption, low cost, support for a large number of network nodes, support for various network topologies, low complexity, fast and reliable operation, and security. ZigBee technology is a new type of technology that relies on wireless networks for transmission and can establish wireless connections at close distances.

ZigBee's inherent advantages have made it a mainstream technology in the IoT industry, with large-scale applications in industrial, agricultural, and smart home fields.

(iii) LoRa: LoRa™ (Long Range) is a modulation technology that provides longer communication distances compared to similar technologies. LoRa is widely used in various IoT products, including LoRa gateways, smoke detectors, water monitoring, infrared detection, positioning, and smart plugs. As a narrowband wireless technology, LoRa uses time difference of arrival for geolocation. LoRa positioning applications include smart cities and traffic monitoring, metering and logistics, and agricultural monitoring.

3. Short-Range Communication

(i) RFID: Radio Frequency Identification (RFID) is a technology that uses radio waves to identify and track objects. It is commonly used for inventory management, access control, and asset tracking.

(ii) NFC: Near Field Communication (NFC) is a short-range wireless communication technology that allows devices to establish communication by bringing them close together. NFC has features such as human-to-machine and machine-to-machine interactions.

(iii) Bluetooth: Bluetooth technology is a global standard for wireless data and voice communication. It provides a special type of short-range wireless technology based on low-cost connections for fixed and mobile devices.

Bluetooth enables wireless information exchange between various devices, including mobile phones, PDAs, wireless headphones, laptops, and related peripherals. By using Bluetooth technology, communication between mobile communication terminals and Internet devices can be simplified, resulting in faster and more efficient data transmission and expanding the possibilities of wireless communication.

4. Wired Communication

(i) USB: USB (Universal Serial Bus) is an external bus standard that specifies the connection and communication between computers and external devices. It is widely used in the PC domain as an interface technology.

(ii) Serial Communication Protocol: The serial communication protocol specifies the contents of the data packets, including start bits, payload data, parity bits, and stop bits. Both parties must agree on a consistent data packet format to communicate properly. Common protocols in serial communication include RS-232, RS-422, and RS-485.

Serial communication refers to the communication between peripheral devices and computers using bit-by-bit data transmission. This communication method uses fewer data lines and can save communication costs in long-distance communication, but its transmission speed is lower than parallel transmission. Most computers (excluding laptops) have two RS-232 serial ports. Serial communication is also a commonly used communication protocol in instrument and equipment industries.

(iii) Ethernet: Ethernet is a computer local area network (LAN) technology. The IEEE organization's IEEE 802.3 standard defines the technical standards of Ethernet, including the physical layer wiring, electronic signals, and media access control protocols.

(iv) MBus: MBus (Meter-Bus) is a two-wire bus widely used for remote meter reading systems, such as heat meters and water meters, based on European standards.

B. Network Layer and Transport Protocols

1. IPv4: Internet Protocol version 4 is the fourth version of the Internet Protocol, which is the first widely deployed version in the protocol's development process. IPv4 is the core of the Internet and the most widely used version of the Internet Protocol.

2. IPv6: Internet Protocol version 6 is developed to address the limited network address resources of IPv4, which significantly restricts the application and development of the Internet. IPv6 solves the problem of network address resource scarcity and enables the connection of multiple devices to the Internet.

3. TCP: Transmission Control Protocol 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. TCP provides reliable communication services between pairs of processes in computers connected to different but interconnected networks. TCP assumes that it can obtain a simple, possibly unreliable data packet service from a lower-level protocol.

4. 6LoWPAN: 6LoWPAN is an IPv6-based low-power wireless personal area network standard, specifically IPv6 over IEEE 802.15.4.

C. Application Layer Protocols

1. MQTT Protocol: MQTT is a publish-subscribe communication protocol commonly used in machine-to-machine (M2M) communication and the Internet of Things (IoT). It is widely used in various applications, including satellite communication between sensors, occasional dial-up medical devices, smart homes, and small-scale devices.

2. CoAP Protocol: CoAP (Constrained Application Protocol) is a lightweight web-like protocol for constrained devices and constrained networks in the IoT world. It is suitable for small, low-power sensors, switches, valves, and similar components that require remote control or monitoring via standard Internet networks. CoAP does not respond to unsupported types.

3. REST/HTTP Protocol: RESTful is a resource-based software architectural style. Resources refer to specific information or entities on the network, such as images or songs. RESTful APIs are implementations based on the HTTP protocol (an application-layer protocol known for its simplicity and speed).

Applications or designs that conform to the REST specification are called RESTful, and APIs designed according to the REST specification are called RESTful APIs.

4. DDS Protocol: DDS (Data Distribution Service) is a middleware protocol for distributed real-time data distribution services. It acts as a "bus on the bus" in distributed real-time networks, facilitating the interconnection of network protocols. It plays a role similar to TCP/IP in real-time networks.

5. AMQP Protocol: AMQP (Advanced Message Queuing Protocol) is an application layer standard for a message-oriented middleware that provides unified messaging services. It is an open standard for application layer protocols and enables messaging between clients and message-oriented middleware without being restricted by different client/middleware products or programming languages. Examples of AMQP implementations include RabbitMQ, which is implemented in Erlang.

6. XMPP Protocol: XMPP (Extensible Messaging and Presence Protocol) is a protocol based on a subset of the XML standard, inheriting the flexibility of XML in an evolving environment. XMPP-based applications have great scalability. Extended information can be sent to meet user needs and establish applications such as content publishing systems and address-based services on top of XMPP.

D. Comparison of Some Communication Protocols

1. Comparison of NB-IoT and LoRa Protocols

Firstly, in terms of frequency bands, LoRa operates in unlicensed bands below 1GHz, which does not require additional fees for application. On the other hand, NB-IoT and cellular communication using bands below 1GHz require licensing and incur fees.

Secondly, in terms of battery life, LoRa modules have unique features in dealing with interference, network overlap, and scalability. However, NB-IoT, due to considerations of service quality, cannot provide the same battery life as LoRa.

Thirdly, in terms of device cost, LoRa protocol is simpler and easier to develop for terminal nodes. It has better compatibility with microprocessors. Low-cost and technically mature LoRa modules are already available in the market, with upgraded versions being released gradually.

Fourthly, regarding network coverage and deployment schedule, the NB-IoT standard was announced in 2016, and besides network deployment, additional time and effort are needed to establish commercialization and the industrial chain. The entire industrial chain of LoRa is relatively mature, and products are in a state of "waiting for takeoff." Many countries worldwide are conducting or have completed nationwide network deployments.

2. Comparison of Bluetooth, WiFi, and ZigBee Protocols

Currently, WiFi's advantage lies in its widespread application, already reaching millions of households. ZigBee's advantage lies in its low power consumption and self-organizing network capabilities. Ultra-Wideband (UWB) technology excels in transmission rate. Bluetooth's advantage is easy networking. However, these three technologies also have their limitations, and none of them can fully meet all the requirements of smart homes.

Bluetooth technology enables short-range wireless communication, but its protocol is more complex, consumes more power, and has higher costs, making it less suitable for applications that require low cost and low power consumption in industrial control and home networking. One of the biggest obstacles for Bluetooth is its limited transmission range, usually around 10 meters. It also has limited resistance to interference and information security issues, which hampers its further development and large-scale applications.

WiFi is also a short-range wireless transmission technology that can provide instant access to wireless signals with high mobility, making it suitable for applications in offices and homes. However, WiFi has a fatal drawback. As WiFi uses radio frequency technology to transmit data signals through the air, it is susceptible to external interference.

ZigBee is an internationally recognized wireless communication technology that allows each network port to connect to over 65,000 endpoints. It is suitable for various fields, including homes, industries, agriculture, etc. ZigBee has the advantages of low power consumption and low cost.

3. Comparison of MQTT and CoAP Protocols

MQTT is a many-to-many communication protocol used for message transmission between different clients through intermediate brokers. It decouples producers from consumers, allowing clients to publish messages and letting the broker handle routing and message copying. Although MQTT supports some level of persistence, it is best used as a real-time data communication bus.

CoAP, on the other hand, is primarily a point-to-point protocol used for transferring status information between clients and servers. While it supports observing resources, CoAP is best suited for a state transfer model rather than event-driven operations.

MQTT clients establish long-lived TCP connections, which usually pose no issues. CoAP clients and servers, on the other hand, send and receive UDP datagrams. In NAT environments, tunnels or port forwarding can be used to allow CoAP or similar types of devices such as LWM2M to initialize frontend connections.

MQTT does not provide support for message typing or other metadata to aid client understanding. MQTT messages can be used for any purpose, but all clients must know the upstream data format to enable communication. CoAP, on the contrary, provides built-in support for content negotiation and discovery, allowing devices to probe each other to find the best way to exchange data.

Both protocols have their advantages and disadvantages, and the choice depends on the specific application.

In conclusion, the selection of IoT communication protocols depends on various factors, including the specific use case, network requirements, power consumption, coverage range, and cost considerations. Each protocol has its strengths and weaknesses, and understanding the characteristics of different protocols is essential to make informed decisions when designing and implementing IoT solutions.