Anatomy and refinement of hubs

If you do a random survey on the street, ask what the Router Network is. I believe that as long as you are not in Silicon Valley. Then, 99% of people say, "network? There is a lot of spam, a lot of boring news, a lot of unhealthy content ......, A lot of small MM. "Well, obviously, people do not care about what the network is composed of and what carries the above information.

As an Internet fan and a network enthusiast, why don't we unveil the network to see what's inside the network? Okay. Let's talk about the hub.

Basic Concepts

In the networks we often come into contact with, most of them use the simplest small-sized LAN in the network, and their composition is simple. Generally, it consists of a computer, network card, network cable, and hub. In such a small network, the hub has the greatest credit, and all the computers in the network use it to transmit information.

What is a hub? The current Ethernet topology uses unshielded twisted pair as the transmission medium. The maximum distance between each network segment is 100 meters. More than 100 meters, you need to use a repeater to expand the topological distance of the network. This is because signal attenuation occurs after long-distance transmission. The function of a repeater is to sort out the signals that have been degraded and become incomplete, re-generate a complete signal and continue transmission. A repeater is the predecessor of a general hub. A hub is a multi-port repeater. Take the hub in Figure 1 as an example. A hub generally has a BNC connector, an AUI connector, and an RJ45 interface ranging from 4, 8, and 16. The general HUB of a foreigner is called HUB. The meaning of "center" is in the E-Paper. It seems that the HUB is indeed very important. Let's call it HUB.

HUB external structure

Let's take (figure 1) as an example to see what they look like.

Is a common 10BASE-T shared hub of TP-Link. It has a BNC port, an AUI port (Figure 2), and 16 RJ45 interfaces.

BNC port (Figure 3): It is a standard cable interface. It can connect to the 50Ω coaxial cable in the 10BASE-2 network standard. Most of our common Ethernet networks are 10BASE-T or 100BASE-T. Therefore, our BNC headers have been basically eliminated. However, if you want to use it for Cascade, its speed also has some advantages.

AUI port (Figure 3): It is a transceiver interface. It is used to connect a signal transceiver that is connected to a crude cable. It is a 10BASE-5 network standard. Like 10BASE-2, it is also in the past.

Power Interface (Figure 4. Yes. How does a Hub work without it? Beside the power interface of our hub, we also marked the parameters of its voltage, frequency, and maximum load current.

Power Switch (figure 4): switch. There is really nothing to explain. If you really don't know what it is for, ask the kindergarten children and they will tell you.

RJ45 interface (figure 5): it is the most common interface. The twisted pair wires connected to the computer Nic in our network are inserted to this interface without exception. RJ45 is an interface in the 10BASE-T network standard and is now widely used. There are 8 groove in it. The groove follows the EIA/TIA568 international standard. In the 10BASE-T network, lines 1 and 2 are transmission lines, and lines 3 and 6 are reception lines. The "UTP" shown in the figure refers to unshielded twisted pair wires.

Cascade ports (figure 6): cascade ports have special functions. Let's just say a few more words. Cascade interfaces are specially used for Cascade operations between hubs. In a network, we may have dozens of machines. Taking our 16-port HUB as an example, if we had 30 machines in the 10BASE-T network, our 16 ports would not be enough in any case.

What should we do?

Right! Just a few more hubs !?

After we have three 16-port hubs, our RJ45 ports have 64 4x16 ports. How can we connect these machines to a single network?

Cascade ports!

In the figure, there is a cascade switch next to the cascade port, which is used to allocate one port as needed. That is to say, in a network without cascade, we turn the cascade button off. In this way, one port can be connected directly to the standard twisted pair cable, just like the other 15 ports. When we need to cascade the HUB, we will turn it on. At this time, the sending and receiving end of the first port is switched, so that we can use a standard twisted pair to connect the two hubs to work together.

Some may ask, "what if my HUB has no Cascade ports? "

Well, then we will replace the dual-wire transceiver line.

OK, everything is done!

Our 30 machines are truly connected to a network.

(Note: In the 10BASE-T network structure, the HUB cascade cannot exceed level 4)

Indicator Light (Figure 7): to better manage and monitor the network, HUB manufacturers have designed some practical indicator lights for us, the following describes the meanings of several commonly used indicators:

BNC/AUI: displays errors caused by BNC/AUI connections. On a 10BASE-T hub, a BNC and AUI interface are reserved for connecting to the coaxial cable. However, they are not provided on the 100BASE-T hub. The light is normally unavailable. If the light is on, it indicates that the connected coaxial cable has a problem, such as BNC connector failure, terminal resistance looseness, short circuit, etc.

Power: Power Light. When the HUB is powered on and switched on, the light is on, indicating that the HUB is powered on.

COL: many of my friends have asked me about the function of the lamp. I cannot tell its meaning from the literal. In fact, it is the Collision header, which displays the transfer Collision situation on the network. Because the CSMA/CD method is used to transmit data over Ethernet, the more workstations there are, the more likely a signal collision will occur. Normally, the light is not on. If a collision occurs in the network at this time, it will flash. The higher the flicker frequency, the more serious the collision.

Link/Rx: refers to the connection and working status lights, which correspond to the RJ45 interface of the HUB, and the number is the same. When the RJ45 port has the correct signal access, the light is on, and its reading and writing signals flash. In this case, information exchange occurs.

Internal Structure of the HUB

After reading the external structure of the HUB, we seem to have some knowledge about it. Let's open it and see how it works.

Figure 8 shows the HUB motherboard. We have integrated a lot of chips we have never seen above. Fortunately, I am a Power Engineering Professional, and I have learned so well about electronic technology ...... Several books. Let's take a look at the main parts.

Power Supply (Fig. 9): The HUB power supply is a process of ac-DC Conversion. It is a typical rectification circuit. We can see the insurance tube and main transformer marked by arrows in the figure. An insurance tube is used to protect the power supply at one side. It will automatically fuse when it is attacked by a large current (beyond its fusing value) to protect its inner side of the device. The main transformer is a transformer, and its principle cannot be clarified here. In the figure, the circle is some electrolytic capacitors, and the size of their heads shows the voltage and capacitance values. There are also three-end voltage regulator and rectification diode. Well, do you have to get bored? No more!

Crystal Oscillator (figure 10): As you know, our networks are composed of digital circuits. in Digital Electronics, all signals are composed of 0 and 1. 0 and 1 are actually the high potential and low potential in the logic circuit.

How does one generate 0 and 1?

Yes pulse!

How is a pulse generated?

That's it! The crystal oscillator we see in the figure generates a certain frequency of pulse signals to achieve our network information transmission. The figure shows a 20 MHz oscillator.

The large chip on the left side of the clock chip is the master control chip of the HUB, which is used to manage and implement the work of the HUB.

How does it work?

Well, I don't know much about it.

How the HUB works

We are so arrogant that we still don't know how the HUB works on the network. Let's talk about how it works.

As its name suggests, HUB is the center of the network. In terms of network, it is a wiring point based on the star network topology. The basic function of a hub is information distribution, which distributes signals received on a port to all ports. Some hubs regenerate weak signals before distributing signals, and some hubs sort the signal timing to provide synchronous data communication between all ports.

In our common LAN, hubs are generally divided into shared and exchange hubs.

Shared hubs cannot improve network performance or detect signal errors. They simply receive data from a port and distribute data through all ports, which is the simplest thing a hub can do. It is an entry-level device for Ethernet with a star topology. The hubs in this article belong to this type. The total bandwidth of the hub is 10 Mb/s. If we connect four workstations, when the four workstations access the Internet at the same time, the bandwidth of each workstation is only 10/4 Mb/s.

A Switch HUB is different from a shared HUB. It supports signal filtering. It only transmits signals to a port with a known address, instead of all ports on the network as a shared hub.

In addition, each port on the exchange hub has a dedicated bandwidth, which allows multiple ports to communicate with each other at the same time without affecting each other. The exchange hub can transmit data through direct transmission, storage forwarding, and improved direct transmission, which is much more efficient than the shared hub.

In the above section, we take a shared entry-level hub as an example to illustrate the structure and simple working principle of the hub. As I have been learning network knowledge, it is inevitable that the content in this article will be light and thin. I hope to hear from you a lot of comments.

Article entry: csh responsible editor: csh