Classification of communication systems

For a zero-based population, the first encounter with communication is a very confusing one -- it's a huge concept, it feels like communication is all-knowing, but blind men and an elephant, i don't know what kind of existence it is. 2G/3G/4G/5g/WI-FI/Lora/NB-IOT/Bluetooth/NFC/Zigbee... ? ... We've heard about countless communication technologies, what kind of relationship they have. 

In fact, to get started in communication, the first step is to understand the interrelationship of communication technology, to establish a complete communication technology knowledge system . There are many ways to classify communications, some are classified by technical characteristics (long/short, high/low, duplex/single) , some by range of use, and some by network owner. Here, I tend to distinguish by using objects The communication network of the whole human world is divided into public network communication, private network communication and ISM frequency band communication . The public network communication, is by the operator provides the service the communication network, faces each consumer user, including the individual user, the home user or the ordinary enterprise user. Its service forms can include cellular mobile communications, fiber-optic broadband, cable television, and so on. And the special network communication, is the special government department or the enterprise user uses the communication network. It can be built and serviced by operators, or built and maintained by government and enterprise users themselves. Rail Transit, civil aviation, shipping, public security, fire, electricity, and so on, are dedicated networks. It should be noted that military network communication is a special kind of private network communication. The last one is the ISM band communication The so-called ISM, is Industrial (Industrial) , Scientific (Scientific) and Medical (Medical) . In order to facilitate the work of industrial, scientific and medical institutions, countries have divided up free frequency bands, allowing them to use them freely at a limited transmitting power.

 As a result, the ISM band is often referred to as the freestanding band. Our WI-FI, as well as Bluetooth and other short-rangecommunications technology, are in the ISM band communications Its signal transmission power is low, the transmission distance is short, will not affect the public network or the private network communication . But, because the frequency band resources are very few, therefore the competition is intense, the network quantity is many, is easy to crowd, causes the mutual interference, the speed will also drop along with it. It is worth mentioning that the use of objects to distinguish, is essentially the use of frequency bands to distinguish. Different frequency bands, for different purposes, there are different objects of use. From a technical point of view, we now have a variety of communication technologies. These techniques, according to their own characteristics, will be used in different scenarios and objects. Some of them can only be used for public networks, and some public networks and private networks general. Different network technology, have their own different network architecture . Such as 4G/5G, fiber-optic broadband public network communications technology and services, because the user scale is particularly large, so the network architecture is particularly complex Taking 4G/5G cellular mobile communication technology as an example, it is divided into wireless access network, bearer network and wireless core network . Each part has its own sub-components, some are concerned with communication channels, some are concerned with data routing and exchange, the technical system is extremely complex. By contrast, short-range technologies such as Wi-Fi and Bluetooth have a very simple architecture because of their short distances. Technologies like NFC, wireless intercom, and even point-to-point communications. These technologies, the focus is not on network architecture, but communication channels. In particular, wireless communication technology, wireless air interface principle of work, is the focus of research . All communication technologies are designed to transmit data In the specific form of business, can be divided into voice communications (telephone) , text communications (SMS) , multimedia communications (pictures, audio, video) In the past, when we began modern communications, the telephone network, also known as circuit switching, was built around the telephone business Circuit switching evolved from the earliest step-by-step and crossbar switches to the Stored program control exchange of the 1970s Program-controlled switch, to put it bluntly, is a circuit switch whose main purpose is voice service. The load mode is also mainly TDM circuit (you can think of it as cable) , can not well meet the needs of packet switching business . After the 1980s, with the rapid development of computer network and multimedia services, data packets can carry all kinds of information, including voice, so the communication network has been transformed into a data communication era . The transmission of data packets, also known as“Packet switching services”, so that the data exchange network, also known as packet switching network TCP/IP technology around packet switching network is the foundation of modern communication network. The so-called wireless communications and wired communications, but the underlying media is different, the upper load, is still mainly data packets.