With the continuous increase of the number of Internet of things devices, the communication or connection between these devices has become an important thinking topic. Communication is very common and key to the Internet of things. Both short-range wireless transmission technology and mobile communication technology affect the development of the Internet of things. In communication, communication protocol is particularly important. It is the rules and conventions that both entities must follow to complete communication or services. This paper introduces several available Internet of things communication protocols, which have different performance, data rate, coverage, power and memory, and each protocol has its own advantages and more or less disadvantages. Some of these communication protocols are only suitable for small household appliances, while others can be used for large smart city projects. The Internet of things communication protocols are divided into two categories: one is access protocol and the other is communication protocol. The access protocol is generally responsible for networking and communication between devices in the subnet; The communication protocol is mainly the equipment communication protocol running on the traditional Internet TCP / IP protocol, which is responsible for the data exchange and communication of the equipment through the Internet.
1、 Physical layer, data link layer protocol
1. Long distance cellular communication
(1) 2G / 3G / 4G communication protocols refer to the second, third and fourth generation mobile communication system protocols respectively.
Narrow band Internet of things (NB IOT) has become an important branch of the Internet of things. NB IOT is built in cellular network and only consumes about 180khz bandwidth. It can be directly deployed in GSM network, umts network or LTE network to reduce deployment cost and realize smooth upgrade. NB IOT focuses on the low-power wide coverage (lpwa) Internet of things (IOT) market. It is an emerging technology that can be widely used all over the world. It has the characteristics of wide coverage, multiple connections, fast speed, low cost, low power consumption, excellent architecture and so on.
Application scenario: the scenario applications brought by NB IOT network include intelligent parking, intelligent fire fighting, intelligent water affairs, intelligent street lamps, shared bicycles and intelligent appliances.
The fifth generation mobile communication technology is the latest generation of cellular mobile communication technology. The performance objectives of 5g are high data rate, reduced latency, energy saving, cost reduction, improved system capacity and large-scale equipment connection.
Application scenarios: AR / VR, Internet of vehicles, intelligent manufacturing, smart energy, wireless medical treatment, wireless home entertainment, networked UAV, Ultra HD / panoramic live broadcast, personal AI assistance, smart city.
2. Long distance non cellular communication
Due to the rapid popularity of home WiFi routers and smart phones in previous years, WiFi protocol has also been widely used in the field of smart home. The biggest advantage of WiFi protocol is direct access to the Internet. Compared with ZigBee, the smart home scheme using WiFi protocol eliminates additional gateways, and the dependence on mobile terminals such as mobile phones compared with Bluetooth protocol.
The coverage of commercial WiFi in urban public transport, shopping malls and other public places undoubtedly reveals the scene application potential of commercial WiFi.
ZigBee is a wireless communication protocol with low speed and short distance transmission. It is a highly reliable wireless data transmission network. Its main features are low speed, low power consumption, low cost, supporting a large number of online nodes, supporting a variety of online topologies, low complexity, fast, reliable and safe. ZigBee technology is a new technology. It appears recently. It mainly relies on wireless network for transmission. It can connect wirelessly in a short distance. It belongs to wireless network communication technology.
The inherent advantages of ZigBee technology make it gradually become a mainstream technology in the Internet of things industry and get large-scale applications in the fields of industry, agriculture, smart home and so on.
LoRa ™ (long range) is a modulation technology that provides a longer communication distance than similar technologies. Lora gateway, smoke detection, water monitoring, infrared detection, positioning, row and plug are widely used in Internet of things products. As a narrowband wireless technology, Lora uses arrival time difference to realize geographic location. Application scenarios of Lora positioning: smart city and traffic monitoring, measurement and logistics, and agricultural positioning monitoring.
3. Short range communication
Radio frequency identification (RFID) is the abbreviation of radio frequency identification. Its principle is non-contact data communication between reader and tag to achieve the purpose of identifying targets. RFID is widely used. Typical applications include animal chip, automobile chip anti-theft device, access control, parking lot control, production line automation and material management. The complete RFID system consists of reader, tag and data management system.
The full Chinese name of NFC is near field communication technology. NFC is developed on the basis of non-contact radio frequency identification (RFID) technology and wireless interconnection technology. It provides a very safe and fast communication method for various electronic products that are becoming more and more popular in our daily life. "Near field" in the Chinese name of NFC refers to radio waves adjacent to electromagnetic fields.
Application scenario: it is used in the fields of access control, attendance, visitors, meeting sign in, guard tour, etc. NFC has the functions of human-computer interaction and inter machine interaction.
Bluetooth technology is an open global standard for wireless data and voice communication. It is a special short-range wireless technology connection based on low-cost short-range wireless connection to establish a communication environment for fixed and mobile devices.
Bluetooth can exchange wireless information between many devices, including mobile phones, PDAs, wireless headsets, laptops, related peripherals and so on. The use of "Bluetooth" technology can not only effectively simplify the communication between mobile communication terminal devices, but also successfully simplify the communication between devices and the Internet, so that data transmission becomes more rapid and efficient and broaden the road for wireless communication.
4. Wired communication
USB, the abbreviation of universal serial bus in English, is an external bus standard, which is used to standardize the connection and communication between computer and external devices. It is an interface technology applied in the field of PC.
(2) Serial communication protocol
Serial communication protocol refers to the relevant specifications that specify the content of data packet, including start bit, main data, check bit and stop bit. Both parties need to agree on a consistent data packet format to send and receive data normally. In serial communication, common protocols include RS-232, RS-422 and RS-485.
Serial communication refers to a communication mode between peripherals and computers that transmits data bit by bit through data lines. This communication mode uses less data lines, which can save the communication cost 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 common communication protocol for instruments and equipment.
Ethernet is a computer LAN technology. The IEEE 802.3 standard of IEEE organization formulates the technical standard of Ethernet, which specifies the contents including the connection of physical layer, electronic signal and media access layer protocol.
MBus remote meter reading system (Symphonic MBus) is a European standard 2-wire two bus, which is mainly used for consumption measuring instruments such as heat meter and water meter series.
2、 Network layer, transmission protocol
The fourth version of Internet communication protocol is the fourth revised version in the development process of internet protocol, and it is also the first widely deployed version of this protocol. IPv4 is the core of the Internet and the most widely used version of the internet protocol
For the 6th edition of internet protocol, the biggest problem of IPv4 is the limited network address resources, which seriously restricts the application and development of the Internet. The use of IPv6 can not only solve the problem of the number of network address resources, but also solve the obstacle of a variety of access devices connecting to the Internet
Transmission control protocol (TCP) is a connection oriented, reliable and byte stream based transport layer communication protocol. TCP is designed to adapt to the hierarchical protocol hierarchy supporting multi network applications. Paired processes in host computers connected to different but interconnected computer communication networks rely on TCP to provide reliable communication services. TCP assumes that it can obtain simple and possibly unreliable datagram services from lower level protocols.
6LoWPAN is a low-speed wireless personal area network standard based on IPv6, that is, IPv6 over IEEE 802.15.4.
3、 Application layer protocol
1. Mqtt protocol
Mqtt (message queue telemetry transport), translated into Chinese, is a telemetry transmission protocol. It mainly provides two message modes of subscription / release, which is simpler, lighter and easy to use. It is especially suitable for message distribution in limited environments (low bandwidth, high network delay and unstable network communication). It belongs to a standard transmission protocol of the Internet of things.
In many cases, including restricted environments, such as machine to machine (M2M) communication and Internet of things (IOT). It has been widely used in communication sensors through satellite links, occasional dial-up medical devices, smart homes, and some miniaturized devices.
2. COAP protocol
COAP (constrained Application Protocol) is a web like protocol in the world of Internet of things. It is applicable to small low-power sensors, switches, valves and similar components that need to be remotely controlled or monitored through standard Internet networks. The server may not respond to unsupported types
3. Rest / HTTP protocol
Restful is a resource-based software architecture style. The so-called resource is an entity on the network, or a specific information on the network. A picture and a song are resources. Restful API is an implementation based on HTTP protocol. HTTP is an application layer protocol, which is characterized by simplicity and speed.
The application or design that meets the rest specification is restful. The API designed according to the rest specification is called restful API
4. DDS protocol
DDS (data distribution service) distributed real-time data distribution service middleware protocol, which is the "TCP / IP" in the distributed real-time network, is used to solve the network protocol interconnection in the real-time network, and its function is equivalent to the "bus on the bus".
5. AMQP protocol
AMQP, or advanced message queuing protocol, is an application layer standard advanced message queuing protocol that provides unified messaging services. It is an open standard of application layer protocol and is designed for message oriented middleware. The client and message middleware based on this protocol can deliver messages, which is not limited by different products and different development languages of the client / middleware. The implementations in Erlang include rabbitmq and so on.
6. XMPP protocol
XMPP is a protocol based on subset XML of standard general markup language. It inherits the flexible development in XML environment. Therefore, applications based on XMPP have strong scalability. The expanded XMPP can handle the needs of users by sending extended information, and establish applications such as content publishing system and address based services at the top of XMPP.
4、 Comparison of some communication protocols
1. Comparison between NB IOT protocol and Lora protocol
First, frequency band. Lora works in the unlicensed frequency band below 1GHz and does not need to pay extra for application. The frequency band below 1GHz used by NB IOT and cellular communication is 2113 authorized and needs to be charged.
Second, battery life. Lora module has unique characteristics in dealing with interference, network 5261 overlap and scalability, but it can not provide the same quality of service 4102 as cellular protocol. NB IOT cannot provide the same battery life as Lora due to the consideration of service quality.
Third, equipment cost. For terminal nodes, Lora protocol is simpler and easier to develop than NB IOT, and 1653 has better applicability and compatibility for microprocessors. At the same time, low-cost and relatively mature Lora modules can be found in the market, and upgraded versions will come out one after another.
Fourth, network coverage and deployment schedule. NB IOT standard was published in 2016. In addition to network deployment, the corresponding commercialization and the establishment of industrial chain still need longer time and efforts to explore. Lora's entire industrial chain is relatively mature, and its products are in a state of "ready for reply". At the same time, many countries around the world are carrying out or have completed national network deployment.
2. Comparison of Bluetooth, WiFi and ZigBee protocols
At present, the advantage of WiFi is that it is widely used and has been popularized to thousands of households; ZigBee's advantages are low power consumption and ad hoc network; The advantage of UWB carrier free wireless communication technology is the transmission rate; The advantages of Bluetooth are simple networking. However, these three technologies also have their own shortcomings. No technology can fully meet all the requirements of smart home.
The emergence of Bluetooth technology makes short-range wireless communication possible, but its protocol is complex, high power consumption and high cost. It is not suitable for industrial control and home networks requiring low cost and low power consumption. In particular, the biggest obstacle of Bluetooth lies in the limited transmission range, the general effective range is about 10m, the weak anti-interference ability and information security are also the main factors restricting its further development and large-scale application.
WiFi is also a short-range wireless transmission technology, which can access wireless signals at any time. It has strong mobility and is more suitable for application in office and home environments. Of course, WiFi also has a fatal disadvantage. Because WiFi uses RF technology, it sends and receives data through the air and transmits data signals using radio waves, which is more vulnerable to external interference.
ZigBee is an internationally accepted wireless communication technology. Each network port can access more than 65000 ports at most, which is suitable for home, industry, agriculture and other fields, while Bluetooth and WiFi network terminals can only access 10 ports, which obviously can not meet the needs of families. ZigBee also has the advantages of low power consumption and low cost.
3. Comparison between mqtt protocol and COAP protocol
Mqtt is a many to many communication protocol, which is used to transmit messages between different clients through intermediate agents, decouple producers and consumers, make the client publish, let the agent decide the route and copy messages. Although mqtt supports some persistence, it is best used as a real-time data communication bus.
COAP is mainly a point-to-point protocol, which is used to transmit status information between client and server. Although it supports observation resources, COAP is best suited to the state transfer model, not entirely event based.
The mqtt client establishes a long TCP connection, which usually means that there is no problem. Both the COAP client and the server send and receive UDP packets. In the NAT environment, tunnel or port forwarding can be used to allow COAP, or like lwm2m, the device may initialize the front-end connection first.
Mqtt does not support message type marking or other metadata to help clients understand that mqtt messages can be used for any purpose, but all clients must know the upward data format to allow communication and COAP. On the contrary, it provides built-in support of content negotiation and discovery, and allows devices to detect each other to find the way to exchange data.
The two protocols have their own advantages and disadvantages, and the appropriate choice depends on their own application.
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