Chapter 413 Let’s Go for Empty Score
The comrades from the Institute of Communications were confused at once. Chief Engineer Gao, are there so many fancy features in the programmable switching system?
It's incredible enough that you proposed one type of switch, and now you have three types at once.

If they could still roughly understand the space-division switch, then the time-division switch and the digital switch were temporarily beyond their knowledge.

But don't just ask, you have to at least tell me what these three types of switches are and what the differences are.

Gao Zhendong then introduced the basic principles, advantages and disadvantages of the three types of switches. Several comrades from the Telephone Institute of the Communications Institute immediately fell in love with the digital switches at first sight. I want this!
However, as the chief engineer of the Institute of Communications, Mr. Feng fell into deep thought.

Ordinary employees only need to care about advanced technology and a sense of accomplishment, but as the chief engineer of the Communications Institute, he has a lot to consider.

"Chief Engineer Gao, first rule out time-division switches. They are neither good nor bad. The basic technical difficulty is about the same as that of digital switches, but in terms of advantages, they always seem to be lacking something."

Mr. Feng’s choice is also the choice of most people. If he didn’t know about digital switches, it would be fine. But after knowing them, the option of time-sharing would be ruled out first.

Gao Zhendong nodded: "Well, Mr. Feng's judgment is basically correct. Time-division switching is the basic technology of digital switching."

Other major countries in the world that research and produce programmable switches also did not stay at the time-division switching stage for too long.

The remaining two types made Mr. Feng very conflicted. One was simple, easy to produce results, and the other was extremely advanced and could be achieved in one step. The world's first practical digital switch was developed by the Gallic Rooster 10 years later.

After thinking it over, he couldn't make up his mind, so he simply asked Shishi to make the decision.

"Chief Engineer Gao, what is your opinion?"

Gao Zhendong smiled and said, "Space separation exchange!"

Seeing that everyone was a little confused, he explained the reason to everyone.

"First of all, the principles of air separation exchange and current manual exchange are extremely consistent, and all the required environmental conditions can basically remain unchanged, allowing for a smooth transition."

Time division and digital switching have higher requirements for line quality. In essence, these two technologies cram more data into the same line. Under the same conditions, Shannon said that the higher the speed, the shorter the distance.

A smooth transition without network transformation is very important for us now, as transformation costs money.

Mr. Feng nodded. Chief Engineer Gao was indeed a thoughtful person. He was not the type who only focused on the technical aspects. He fully considered all aspects of the situation before making a decision.

The point Gao Zhendong just mentioned is exactly the point that Mr. Feng has considered the most and is the most difficult to give up. He also understands Shannon's theorem. Although Shannon lived until 2001, "Communication in the Noise" was published in 1949. At that time, Shannon was 33 years old.

“Secondly, the cost of digital switches is too high at the moment.”

As for the modulation technology of digital switches, Gao Zhendong planned to directly use the most widely used PCM in one step. At that time when integrated circuits were not yet developed, both ends of the call needed to perform an A/D (analog-to-digital) and a D/A (digital-to-analog) conversion, and the circuit cost was very high.

Moreover, in addition to this part of the circuit cost, the digital switch requires more memory, which further increases the cost of the digital switch.

No one was as familiar with this area as Gao Zhendong. When they heard Gao Zhendong talk about it, they realized that there was such a thing.

However, Mr. Feng still raised his concerns: "Mr. Gao, if we switch from program-controlled air-separation switches to popular program-controlled digital switches in the future, will the existing air-separation switches be left idle and wasted?"

Gao Zhendong shook his head: "No, as long as we add conversion equipment to the air-separation switch, it can be easily integrated into the digital switching network."

就拿1970年第一个搞出数字交换机的高卢鸡来说，其1981年的计划是1983年将1/3的用户接入数字交换机，1990年至1992年实现交换机的全部数字化。

Before this, a mixed network of space-division switches and digital switches was used.

Even the Gallic rooster, which once had such a glorious history in telecommunication equipment, needed such a long process to achieve full digitalization, let alone us now. Being advanced is not necessarily important, but being suitable is important.

However, even the Gallic roosters themselves probably could not have imagined that their glorious telecommunications industry would eventually be sold out.

After listening to Gao Zhendong's analysis, Chief Engineer Feng also made up his mind.

"Mr. Gao, let's start with a program-controlled air-separation switch."

In the original time and space, between the 60s and 70s, we had a history of being too ambitious, ignoring actual technical foundation, blindly pursuing technological advancement, irrationally raising parameter requirements, and forcing projects into operation.

In the end, the results are mostly not very good. Money is spent, time is wasted, but the results are basically very limited.

Gao Zhendong was very clear about this, so naturally he would try to avoid this situation as much as possible within the scope of his control.

Gao Zhendong nodded: "Well, that's fine, let's decide first and lean towards this."

Now that the direction has been decided, the things that can be done have also been decided. "Mr. Feng, before you get further status data back, we can do three things first."

Chief Engineer Feng picked up the pen and said, "Please go ahead, Mr. Gao."

"The first thing is to determine if we have a suitable reed relay. If not, can we get one to copy? If not, can we get a suitable ordinary relay?"

The residual spring relay is a state-holding relay that can use residual magnetism to maintain the working state without the need for continuous power supply. To put it bluntly, it saves electricity.

Although a single relay may not seem to consume much electricity, a large-scale switch may have tens of thousands of relays, which together consumes a lot of electricity.

This is the choice of Citigroup's employees on air separation switches. Nowadays, Citigroup's employees are still trustworthy and are not the kind who write random PPTs.

The Japanese, like other major switch-producing countries, solved this problem, but they took a different approach, using mechanical retention. The Japanese's brain circuits are always different.

Chief Engineer Feng was not sure whether there were any reed relays left, so he made a note of this matter.

A comrade from the Telephone Research Institute knew something about other relays: "Chief Engineer Gao, we have copied the РПН flat relay. It should work, right?"

It was the thing in the old Russian Type 47 telephone exchange. Gao Zhendong felt that the size and weight of this thing was a bit difficult to hold: "That one is a bit too big. Let's use it as a last resort."

He didn't reject it outright, so as to save some face.

Mr. Feng thought about the stone that could kill people and laughed. He understood what Gao Zhendong meant.

"The second thing is to imitate a telephone, the kind with a dial. The dial generates a pulse with a duty cycle of 1.3/1, and the maximum pulse frequency is 20Hz."

In my country, dial-type telephones were still high-end products until the 80s. Most units used hand-cranked telephones. In fact, it was not that the telephones were high-end, but the problem was with the switches.

This type of number dial is actually a pulse generating device. When the number dial is turned, the number dial will automatically generate a corresponding number of pulses based on the rotation distance of the number. The number "1" is 1 pulse, "2" is two, and so on.

This is also the reason why the 0 in old dial-up phones is at the end, a "0" is 10 pulses!
As for why Gao Zhendong didn't just make a push-button phone, the problem is still the same: push-button phones are expensive! The circuit that uses the push-buttons to generate the corresponding number of pulses is much more expensive than the number dial these days.

As for the DTMF (dual tone multi-frequency) signal actually used by push-button telephones, forget it. It uses two frequency signals to represent numbers. As soon as you hear the name, you know that this is much more troublesome than 20 pulses per second in this day and age.

Anyway, this thing is easy to imitate. Even if Gao Zhendong’s requirements may not be the same as the prototype, it is not difficult to modify.

The comrades from the Communications Institute are full of confidence. I am familiar with this thing!

"Third, I'd like to share with you some of my thoughts on program-controlled switches. Please go back and read them and give me some suggestions."

Look, Chief Engineer Gao is so modest, just “giving some suggestions”.

The comrades at the Telephone Research Institute were very excited about this unexpected discovery. Judging from what Chief Engineer Gao had just said, these research results would definitely be of great benefit to them.

Even Chief Engineer Feng was very interested in this. He participated in the imitation of Type 47 and knew the structure, components and installation of Type 47.

But why this structure is adopted, why rotary selectors and lifting selectors are combined with relays, why so many of these devices are used instead of more or less, to be honest, they really don't know clearly, or they don't understand it systematically and thoroughly enough.

In short, the theoretical foundation is weak, and this statement will still be correct even after decades.

Gao Zhendong fumbled around in the safe for a long time, then came back and handed a stack of manuscripts to Chief Engineer Feng.

The comrades from the Communications Institute looked at Gao Zhendong’s safe with envy. What good things might be inside it?

But they also knew that if anyone dared to steal this safe, the rest of their lives would be in jeopardy.

In fact, there is nothing important in this safe, it is just a scapegoat.

Chief Engineer Feng quickly took it and took a sneak peek.

The manuscript was not thick, only about thirty or forty pages, and the content looked simple, but it made Chief Engineer Feng very jealous.

The basic composition and functions of the switching system, basic knowledge of telephone traffic, network structure of telephone circuits, control methods, and signaling methods.
They are all basic knowledge, but they are all very theoretical. It just so happens that what is lacking is theory.

(End of this chapter)