What exactly is communication?(Episode 2)

I didn't finish it last week, and I continued to write today.

█ The layered thinking of communication

The most important step of studying communication technology is to build a communication knowledge system.

The secret of building a communication knowledge system is to establish "stratified thinking".

The layered thinking of communication is divided into "big layered" and "small stratification".

Let's take a look at the "big layered" first.

In the previous episode, I told you the evolution of the communication network.

An important driving force for the evolution of the communication network is the rapid expansion of the number of communication nodes.

In other words, the communication network is from "Point to Point" to "Point to Multipoint", and then from "point to multiple points" to "multipoint to multipoint )"the process of.

The number of nodes involved in communication rapidly expands, and eventually reached the scale of 100 million (Internet of Internet of a network) or even tens of billions (the Internet of Things).

The most primitive and basic communication model is to communicate between the two nodes. In this case, a communication line is fine.

When there are more than two nodes participating in the communication, we network is involved. There are also networking methods such as chain, star, ring, tree type.

When the scale of nodes continues to expand, people find that just like the pyramid management architecture is the most practical human tissue structure. The tree network structure is the simplest and efficient large -scale communication group method.

Tree type (pyramid type)

This method of "small nets together and turning into a large net" is a typical centralized networking method.

No matter what kind of networking method is, as long as there are many nodes, it involves routing and exchange. In other words, at each convergence node, you need to rout or point the communication data and exchange information content, which is equivalent to an intersection and gateway.

Each node must be judged

Tree networks are widely adopted by operators and become the foundation of the public communication network. (Of course, other networking methods such as ring network are also appropriately adopted as supplements.)

For tree -type networks, which are constantly "converging", we generally divide them into three layers, from the bottom to top are access layers, convergence layers, and core layers.

The access layer is responsible for connecting the user into the network; the gathering layer is responsible for gathered and distributed data; the core layer is the network backbone.

We can understand it as a courier company. There will be express stations near each community to reach users, collect and send express delivery. The goods at the express station will be delivered to the express delivery point of the previous level, and then the higher level will be transferred to the level.

Different layers involve different communication technologies. In other words, between nodes and nodes, the communication technology adopted may not be the same. Because the environment and conditions they live are different, the amount of data be carried is different.

For example, on the access layer, users should be connected to the network, because users may have mobility and run around. Then, wireless communication technology will be widely used, such as 4G/5G, Wi-Fi, etc.

5G antenna

At the convergence layer, because the amount of data from gathered is very large, the convergence nodes and upper nodes usually use large -capacity optical fiber communication technology (such as OTN).

Fiber

Of course, if the distance between the access nodes and the upper nodes is far away and in remote areas such as deserts, wireless communication technology such as microwave and satellite will also be used.

Microwave antenna

If you use the courier system to metaphorically, the express delivery master of the express station will ride a tricycle to choose the route freely. Between the courier transport point, a car or charter machine will be used for direct transportation.

What we said above is a layered thinking for the network architecture, that is, "big layered". Different sizes of networks are not necessarily the same, but layered thoughts are unchanged.

What is "small layered"?

When you study the specific point -to -point communication, you will encounter "small layered" thinking. Students with engineering backgrounds know the famous TCP/IP models and OSI models, which are typical "small layers".

Communication is a very complicated process. The reason for "small layers" is for their duties. Each layer is a society. Between different levels, "language (protocol)" is not accessible and cannot be directly dialogue.

Regardless of the communication technology, in fact, the model of "small layered" is followed. In fact, the protocols they choose are different.

"Small layered" is actually the "packaging" idea of ​​the express delivery -I write the text on the letter paper, stuff the letter paper into the envelope, and seal the envelope into a larger envelope, or post bags and parcels.

In this way, after the packaging step by step, it is sent to the other side.

After the other party receives it, it will be unpacked step by step to interpret the content. Or, then seize the content to the next -level node through another channel.

"Small layered" also has a taller name, which is the "protocol stack". Each layer of mine must be matched with each layer of you so that we can achieve the top -level business.

4G network protocol stack example

Communication, especially the operator's public network, often involves the connection between the bureau and the end of the bureau. Novices often do not understand the idea of ​​"small layers".

The correct docking method should start with the bottom. Let's take a look at the physical layer that is not connected (whether there is light in the light port, whether the power outlet is electric), and then connect the layer step by layer. When each layer is connected, between the bureau and the opposite bureau, then Realize business -oriented. All in all, the "big layered" thinking is used to study the overall structure of the communication network. "Small layered" thinking is used to understand the specific working principle of communication technology. With these two thinking, you will have clear ideas to study any communication technology.

█ Wired communication and wireless communication

As mentioned earlier, wired and wireless communication is mentioned. Here, we still have to introduce their differences in detail.

In the history of modern communication, the birth time of wireless communication is not too late. However, for a long time after it was born, this technology belongs to the "noble" technology, and only a small number of people can use it.

The reason is very simple, because basic technologies such as electronic technology, material technology and signal processing technology are developing in the early days, resulting in the ability to perfectly control radio electromagnetic waves.

After the foundation of the wireless electromagnetic theory, people have been trying to use the mysterious power of radio electromagnetic waves.

Different frequencies (wavelengths) radio electromagnetic waves have different physical characteristics. The development of mankind's radio waves is actually using these different characteristics for different purposes. For example, high -frequency γ -rays have great lethality and can be used to treat tumors.

From a macro perspective, radio waves are mainly divided into radio waves and light waves (as shown above). Marco and Popov, which created the precedent of using radio waves for communication.

With the technical level at the time, they could only use low -frequency radio waves for wireless communication.

Radio electromagnetic waves are not a "inexhaustible and inexhaustible" resource. Its resource scarcity is reflected in the spectrum (frequency interval). In a certain space range, once a frequency of radio waves are occupied, if others also try to use (signal that transmits this frequency), it will cause interference.

The advantage of low -frequency radio waves is the farther transmission distance. As we all know, the wireless electromagnetic wave with a lower frequency has a longer wavelength (the frequency × wavelength = the speed of light, the speed of light is constant value), and the shooting capacity is stronger, so the communication distance is farther.

The higher the frequency, the shorter wavelength, worse the shooting capacity (the loss of penetration will be larger), and the transmission distance is closer.

The disadvantage of low -frequency radio waves is that resources are very scarce. If FDMA frequency points are used, the number of users is very small and cannot be perfectly used for public mobile communication.

Later, with the continuous breakthrough of basic technologies, we have reused technologies such as TDMA, CDMA, OFDMA, to accommodate more users under a small number of frequency resources.

For example, we imagine frequency resources as a room. If the room is divided into different spaces, different users chat in different rooms.

If in this room, let someone speak at a certain time, and the next time, let another person talk, is the time of time (TDMA).

If everyone speaks in their own language, some people speak English, some people speak French, and some people speak Chinese, that is, the code division (CDMA).

At the same time, we also have the ability to drive a higher frequency of radio electromagnetic waves, which further expands the frequency use range of wireless communication, and finally realized the continuous expansion of communication capacity and continuously increased the connection rate.

This is the same as the highway. The wider the road, the more vehicles that can accommodate at the same time. Moreover, the larger the models that can be accommodated. The greater the transportation capacity of highways.

We have also made great breakthroughs in coding technology and diversity technology, and gradually figured out the characteristics of the metaphysical technology of wireless communication, further reducing the error rate and improving the efficiency of wireless channels.

In this way, we have continuously evolved from 1G to 5G, and successfully developed wireless communication from the "noble" technology into "mass" technology, so that everyone can enjoy the convenience it brings.

The main advantage of wireless communication technology is that it breaks space restrictions, mobility restrictions, and appropriately save costs. If it is a simple competition performance (such as transmission rate, delay, stability, etc.), wireless communication is completely beaten by wired communication.

Interestingly, although the current cable communication is powerful, it is essentially the "blood" of wireless communication.

Early wired communications have always been communicated with cable metal cables with power signal pulse. In the 1960s and 1970s, the fiber was born, breaking this situation.

Fiber communication uses light waves, and light waves are wireless electromagnetic waves, isn't it?

However, traditional wireless communication is spreading in the air. The transmission path is too complicated, too much interference, and the uncertainty is too great. Therefore, optical fiber communication is transmitted in the pure glass fiber core, which is isolated from the outside world, which greatly improves stability.

Wireless Communication vs optical fiber communication

This is like a closed -dedicated lane. A high -speed rail can be desperately accelerated to improve efficiency.

Fiber is one of the greatest inventions in human history. It uses the lowest cost to achieve the maximum return.

Imagine if we have no fiber and only metal cables, then how many valuable metals need to use the current dense communication backbone network? How expensive our communication costs are passed on to users? At present, optical fiber replacing metal cables is the general trend. The backbone network and access network of communication operators have long achieved "light in -copper".

The main defect of optical fiber communication is that it is still relatively fragile in physics. In addition, the fiber fiber measing has a certain technical threshold. The cost of optical interface and optical module is still slightly higher, so it cannot completely replace the network cable.

However, in the foreseeable future, optical fibers will be connected to each computer, each TV, and all terminals that need wired connections.

All wired communication uses optical fiber, and wireless communication uses high-efficiency wireless air port technology (such as 4G/5G/Wi-Fi 6), which is the goal of human communication development. They will jointly support the huge scale and bandwidth needs of humans.

Well, if everyone likes this series, I will continue to write down later, and sort out all the basic knowledge concepts from beginning to end.

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