Siheyuan: Starting from a fitter

Chapter 166 Local Area Networks
In order to ensure that the local defense forces and overseas defense forces of a certain country still have certain survival and counterattack capabilities after being hit by the first H attack, the Ministry of National Defense of a certain country believes that it is necessary to design a decentralized command system.

It consists of scattered command points. When some command points are destroyed, other points can still work normally, and these points can continue to maintain communication by bypassing those command points that have been destroyed.

The Ministry of Defense of this country strongly supports the research of networking, and it started to go online in December 1969.

Its purpose is to re-establish the country's leadership in JS technology application development.The network transmission capacity at that time was only 50Kbps, which was very low by standards.

Initially 15 nodes and a total of 23 hosts were connected.

By 1972, the number of outlets had reached 40, and these 40 outlets could send small text files to each other.At that time, this kind of file was called email, which is our current E-mail.

With the use and in-depth research of the network, the TCP/IP protocol appeared in 1973.

Li Guocheng did not expect that his unintentional move would also attract the attention of the Huaxia military, and the starting point was so similar.

After pondering for a while, Li Guocheng prepared to adopt a transitional plan to accumulate application experience first, and then just set aside time for the development of the TCP/IP protocol.

Of course, the ideas can be used for reference, but the name must no longer be called TCP/IP protocol.

The word "Kyushu Internet" rushed into Li Guocheng's mind. Kyushu was the name of China in ancient times, and it can also refer to the major states in the world.

Thinking of this, Li Guocheng said: "I have a transition plan here, the communication protocol is relatively simple, the rate can reach 500Kbps, and the distance of 1 kilometer is no problem.

The communication protocol of the final solution is relatively complex, and the communication rate should be able to reach 10Mbps.But now it is just an idea, it needs time to study, and the specific delivery time is uncertain.

The advantage of using the transition plan is that you can accumulate experience and discover problems in communication, and we can modify it together until it finally meets actual use.All experiences were then transferred directly to the final solution.”

Li Guocheng finished his thoughts in one breath and waited for their conclusion.

The three bowed their heads to discuss for a while, and Ma Jianmin asked, "Is 1 kilometer the longest communication distance? Is there a way to extend it?"

"Oh, I didn't make it clear. The maximum length of a small LAN I was referring to is 1 kilometer. If a repeater is used, the distance can still be extended a lot. In theory, it can be infinitely long," Li Guocheng replied.

The three of them looked at each other, their eyes full of joy, and lowered their heads to discuss for a while.

"That's great! We chose the transition plan. But there is a suggestion that the pre-embedded cables must consider reserving the cables of the final plan," Ma Jianmin said.

Li Guocheng just pondered for a while, "We can consider designing a universal cable. Then we only need to replace the relay and the cable does not need to be moved."

"That's even better. It's settled like this. Let's start with the transitional plan first," Ma Jianmin said happily, without soliciting the opinions of the other two.Li Guocheng understood that Ma Jianmin was the leader.

One month was set to get the plan, and samples would be delivered in half a year for them to test.

After the three people left, Li Guocheng said to Li Huaide: "Director, this system is too huge. We only have three people in the software team. It will definitely not be completed. You have to find a way."

"How many people do you need?"

"At least 5 people, the more the better," Li Guocheng said with a smile.

"You little monkey, there are at most 5 people, is there more?" Li Huaide saw Li Guocheng's intention.

Li Guocheng deliberately pretended to be heartbroken, but in fact he was already happy inside.His minimum expectation is for two people. He said this deliberately to give Li Huaide leverage to manipulate him in the future.

Li Guocheng, who returned to the laboratory, called Yan Jiefang and Zhang Zhijing to the office and helped them make tea.

"There is a task now, which is quite urgent. We all have to suspend the task at hand."

"What mission is it? It's so urgent," Zhang Zhijing asked.

"We need to develop a communication network for the military, similar to 485, but the speed and distance are far beyond the 485 bus."

Next, Li Guocheng explained to them the knowledge of the Internet and the changes it has brought to the national economy and people's livelihood.After listening, the two felt that they had entered a new field. They were eager to realize the Internet described by Li Guocheng.

Jiuzhou Internet defines a four-layer architecture, from low to high: physical layer, link layer, network layer and application layer. Li Guocheng instilled network knowledge into them based on his own understanding.

He is not afraid of misunderstandings at all, because as long as he grasps the accurate direction, he can fumble and correct everything else, because now everyone is groping.

In communication theory, he stood directly on the shoulders of giants. The university education gave him a general understanding of the basic theory of communication. One year of practice in the computer room gave him a framework for understanding the network.

The only thing that makes him difficult to grasp is the speed of the current chip, which restricts his performance, but based on the development of the first-generation chip, he can start from the basics, but the network communication will be more basic and in-depth.

After an explanation, the two had a basic understanding of the Internet.

"Xiao Zhang, you should focus on how to build the network layer. Jiefang, you should first familiarize yourself with the hardware structure of Kyushu Internet V1.0, and focus on contacting the cable factory.

If they don't know how to produce a characteristic impedance cable, you tell them the cable parameters and then tell them how to test the impedance.If not, provide them with a set of electric bridges, remember to charge a fee."

After the two left, Li Guocheng put away the draft he had sketched just now, and began to build the network chip in his mind.

Taking into account the actual situation of the country, we do not want to make major changes to the 103-type motherboard for the time being. We will try to make partial modifications to meet the actual use, so that we can have money left to upgrade the host.

The connection between the 485 chip and the CPU is a parallel port bus, and the external connection is a serial differential bus, with a characteristic impedance of 150 ohms.A total of two 485 channels are reserved on the motherboard.

It can just be replaced by PIN to PIN. The reserved pins on the 485 chip can be connected to a 12V voltage by flying wires on the motherboard, and a ±12V differential output can be output, which can be transmitted over longer distances.

The new chip can refer to the later CAN2.0 protocol, but it needs to be modified. The frame header, frame tail, and arbitration can be retained, but the data cannot be 8 bytes. It can be modified to a maximum of 128 bytes.

In this way, the voltage is increased to resist voltage attenuation over long distances, the data frame becomes longer, and the effective rate is ensured.

The data rate is tentatively set at 500Kbps, which is better than their 50Kbps.

Li Guocheng's greatest confidence is that the world only realized signal integrity and electromagnetic interference in the 80s, but we have already considered them in our current design.

The external interface chips have built-in electrostatic protection circuits, the circuit board design has considered signal integrity and impedance matching, and the overall machine design has considered EMC.

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(End of this chapter)