About the Internet of Things Communication Protocol (communication Protocol)

One, the distinction between communication and communication protocol:
1, the traditional meaning of "communication" mainly refers to telephone, telegraph, telex. The "message" of the communication means the messages, and the media messages are passed from one end to the other through the communication network. The content of media message is mainly voice, text, picture and video image. The composition of its network is mainly composed of electronic equipment system and radio system, and the signal of transmission and processing is simulated. Therefore, the word "communication" should refer specifically to the use of telegraph, telephone, network and other media transmission system to achieve the above media information transmission process. The "communication" is heavy in the content form, so the communication protocol mainly concentrates on the application layer in the ISO seven layer protocol. The communication protocol is mainly a device 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.

2, communication "refers to data communication only, that is, through the computer network system and communication system to achieve the end-to-end transmission." The communication "letter" refers to the information (information), the information carrier is the binary data, the data can be used to express the traditional media form of information, such as sound, image, animation and so on. "Communication" weighs on the means of transmission or use, from this point of view, the concept of "communication" includes the "transmission" of information. Therefore, the communication protocol mainly concentrates on the physical layer, the data link layer, the network layer and the Transport layer in the ISO seven layer protocol.

3, in the Internet of things applications, communication technology includes Wi-Fi, RFID, NFC, ZigBee, Bluetooth, LoRa, NB-IoT, GSM, GPRS, 3/4/5g Network, Ethernet, RS232, RS485, USB, etc.

4, the relevant communication protocol (Protocol stack, technical standards) includes: Wi-Fi (IEEE 802.11b), RFID, NFC, ZigBee, Bluetooth, LoRa, NB-IoT, CDMA/TDMA, TCP/IP, WCDMA, TD-SCDMA , Td-lte, Fdd-lte, TCP/IP, HTTP, and so on.

5. The communication protocols used in the IoT Technology Framework System are: AMQP, JMS, REST, Http/https, COAP, DDS, MQTT, etc.

Second, the communication protocol:
1. Introduction to HTTP protocol
HTTP is an object-oriented protocol belonging to the application layer, which is suitable for distributed hypermedia information System because of its simple and fast way. It was proposed in 1990, after several years of use and development, has been continuously improved and expanded. Currently used in the WWW is the sixth edition of Http/1.0, http/1.1 standardization work is in progress, and Http-ng (Next Generation of HTTP) has been proposed.

2. HTTP protocol Features
"1" supports client/server mode
"2" Simple and fast
"3" Flexible
"4" No connection
"5" No Status

3. Introduction to HTTPS protocol
The protocol uses the HTTP protocol, but HTTPS uses a different default port than the HTTP protocol and an encryption, authentication layer (between HTTP and TCP). The initial development of this Protocol, conducted by Netscape, provides an authentication and encryption method of communication, which is now widely used for security-sensitive communications on the Internet.

4. The steps for client cloud Web server communication are as follows:
The "1" customer accesses the Web server using the HTTPS URL and requires an SSL connection with the Web server.
When the "2" Web server receives a client request, it sends a copy of the Web site's certificate information (the certificate contains the public key) to the client.
The browser of the "3" client and the Web server begin to negotiate the security level of the SSL connection, which is the level of information encryption.
The browser of the "4" client establishes the session key based on the agreed security level, then encrypts the session key using the public key of the website and transmits it to the website.
The "5" Web server decrypts the session key with its own private key.
The "6" Web server uses the session key to encrypt communication with the client.

5. Introduction of Webserivce/rest protocol
WebService and rest are not protocols, they are based on a technical approach or style of Http/https, and are placed here because the WebService and restful APIs are often used in the external interface approach of IoT application services.

5.1, Webserivce Introduction
The "1" WebService is a remote invocation technique across programming languages and cross-operating system platforms.
"2" xml+xsd (XML Schema), soap and WSDL are the three technologies that make up the WebService platform.
The "3" XML solves the problem of data representation, but it does not define a set of standard data types, much less how to extend this set of data types. XML Schema (XSD) is a set of standards specifically designed to address this problem. It defines a standard set of data types and gives a language to extend this set of data types. The WebService platform uses XSD as its data type system.
The "3" SOAP protocol defines the format of the SOAP message, which is based on the HTTP protocol, and SOAP is based on XML and XSD, where XML is the data encoding of soap. A metaphor: HTTP is the normal highway, XML is the middle of the green barrier and both sides of the fence, soap is the ordinary highway through the belt and the fence has been modified highway. The formula is: SOAP protocol = HTTP protocol + XML data format
The "4" WSDL (Web Services Description Language) is an XML-based language that describes the WEB service and its functions, parameters, and return values.

5.2. Rest Introduction
Rest is a representation of state transitions, a communication style developed based on the HTTP protocol, and is not currently a standard. Rest is the service Call API encapsulation style in the Internet, in the IoT application system, in the IoT application system, the data service can be opened by open Rest API and called by other applications in the Internet.

6, CoAP (Constrained application Protocol) Agreement Introduction
COAP protocol Abbreviation: Limited application protocol, applied in Wireless sensor network protocol. Coap is a simplified HTTP protocol for RESTful API,COAP is the application layer protocol in the 6LowPAN protocol stack, applicable to: IP networks in resource-constrained communications.
"1" header compression
"2" Method and URIs
The "3" Transport layer uses the UDP protocol
"4" Supports asynchronous communication
"5" Support resource discovery
"6" Supports caching

7. Introduction to MQTT (Message Queuing Telemetry Transport) agreement
"1" Introduction
Message Queuing telemetry transmission, an Instant messaging protocol developed by IBM, is more appropriate than a communication protocol for IoT scenarios. The MQTT protocol uses the Publish/subscribe model, all IoT terminals are connected to the cloud via TCP, and the cloud manages the communication content of each device in a themed way, and is responsible for forwarding messages between devices and devices. Suitable for: Provide data transmission and monitoring of remote devices based on cloud platform in low bandwidth and unreliable network.

"2" Use features
"1" uses the agent-based publish/Subscribe message pattern to provide a one-to-many message release;
"2" uses TCP/IP to provide network connection;
"3" small transfer, the overhead is very small (fixed-length head is 2 bytes), protocol Exchange minimized, to reduce network traffic;
"4" Support QoS, there are three kinds of message publishing quality of service: "At most once", "at least once", "only once".

"3" Application scenario
"1" has a php,java,python,c,c# and other language version of the framework of the Agreement;
"2" an important part of IBM Bluemix is its iot,foundation service, a cloud-based MQTT instance;
"3" mobile apps also started using MQTT, such as Facebook Messenger and COM.

8. Introduction to the DDS (Data distribution Service for real-time Systems) protocol
"1" Introduction
The data distribution service for real-time systems, which is the protocol proposed by the famous OMG organization, should be able to prove the future application prospects of the protocol. Suitable for: Distributed high reliability, real-time transmission equipment data communication. At present, DDS has been widely used in defense, civil aviation, industrial control and other fields.

"2" Use features
"1" data-centric;
"2" Using agentless Publish/Subscribe message mode, point-to-point, point-to-many, many-to-many;
"3" provides 21 kinds of QoS service quality policy.

9. Introduction to AMQP (Advanced Message Queuing Protocol) agreement
"1" Introduction
Advanced Message Queuing protocol, which was proposed by Oasis, the organization has proposed the OSLC (Open Source Lifecyle) standard for: Business systems such as Plm,erp,mes for data exchange.

"2" protocol features
"1" Wire-level protocol, which describes the format of the data transmitted over the network, in bytes as a stream;
"2" for messages, queues, routing (including point-to-point and publish/subscribe), reliability, security;

The "3" open source agreement includes:
The implementation of the 1 Erlang is RABBITMQ
"2" AMQP's Open Source implementation, written in C language openamq
"3" Apache qpid
"3" stormmq

10. Introduction to XMPP (extensible Messaging and Presence Protocol) protocol
"1" Introduction
Extensible communication and presentation protocol, the predecessor of XMPP is Jabber, an open source form of organization-generated network Instant Messaging protocol. XMPP is currently being standardized by the IETF International Standards Organization. Applies To: Instant messaging applications, but also in network management, content feeds, collaboration tools, file sharing, gaming, remote system monitoring and so on.

"2" protocol features
"1" client/server communication mode;
"2" distributed network;
"3" Simple client, put most of the work on the server side;
The data format of the subset XML for the standard generic markup Language of "4".

"3" Precautions
XMPP is an XML-based protocol, which is widely used in Internet communication applications due to its openness and ease of use. Relative HTTP,XMPP in the business process of communication is more suitable for the IoT system, developers do not have to spend too much effort to solve the communication process of equipment communications, relative development costs will be lower. But the security of the HTTP protocol and the cost of computing resources have not been solved in essence.

11. Introduction to the JMS (Java Message Service) protocol
"1" Introduction
Java Messaging Service, which is the famous Message Queuing protocol in the Java platform. The Java Messaging Service application interface is an API for message-oriented middleware (MOM) in the Java platform for sending messages between two applications, or distributed systems, for asynchronous communication. The Java Messaging Service is a platform-agnostic API, and the vast majority of MOM providers support JMS. JMS is a vendor-agnostic API for accessing messaging system messages, similar to JDBC (Java Database
Connectivity).

About the Internet of Things Communication Protocol (communication Protocol)