Network Transmission Media
What are the transmission media of the network?
Network transmission media refers to the carrier that transmits information in the network. Commonly used transmission media are divided into two categories: wired transmission media and wireless transmission media.
⑴Wired transmission medium refers to the physical connection part completed between two communication devices. It can transmit signals from one party to the other. Wired transmission media mainly include twisted pair, coaxial cable and optical fiber. Twisted pairs and coaxial cables transmit electrical signals, and optical fibers transmit optical signals.
⑵The wireless transmission medium refers to the free space around us. We can use radio waves to communicate in free space to complete a variety of wireless communications. The electromagnetic waves transmitted in free space can be divided into radio waves, microwaves, infrared rays, lasers, etc. according to the frequency spectrum, and the information is loaded on the electromagnetic waves to stop transmission.
Different transmission media have different characteristics. Their different characteristics have a great influence on the data communication quality and communication speed in the network!
What are the network transmission media?
Transmission medium
Twisted pair is made up of two uranium wires covered with an insulating sheath, which are twisted together. We call this twisted pair of positive and negative wires as a pair. This is the most fundamental unit of measurement for twisted pair cables.
What is commonly seen in the market is that each twisted pair is composed of four pairs of wires, and the identification is marked in four colors of orange, blue, green, and comprehensive (specifically, orange, white orange, blue, white blue, green, Eight colors of white-green, brown, and white-brown), that is, there are 8 copper wires. Its appearance is shown in Figure 4-11.
Because unshielded twisted pair UTP is widely used in the market, the American Electronics Industry Association and the Remote Communications Association (EIA/TIA) have formulated the "cable grade: of UTP cable. They are secondary The difference lies in the lay length of the winding. Generally, the denser the two wires are wound, the smaller the lay distance, and the better the transmission function of the communication room.
Type 1 line: if the golden wire is not wound, it can only transmit sound but not data;
2 Category wire: no winding, can transmit data. The maximum transmission rate is 4Mbps;
Category 3: copper wire is wound once per decimeter, the most commonly used in the late market, the maximum transmission rate is;
Category 4: is a transitional wire, The market is rare, and the maximum transmission rate is;
Category 5 line: is the beginning of our high-speed development, and the maximum transmission rate is;
Category 5 line: new wire material presented in conjunction with the appearance of gigabit network;
Category 6 line : A new generation of high-speed wire, it is estimated that it will go through a standard proposal this year.
1. Thick coaxial cable 
Thick coaxial cable is used by cable manufacturers as its code name. This code is also often used on the general skin in the line. Its specifications are as follows:
Line width: 1.27 cm
Maximum transmission interval: meters
Impedance: 50 ohms
Features: The line is thicker, so the flexibility is less, and the manufacturing method is more complex, you will encounter order trouble when installing indoors; but its maximum The transmission interval is much larger than that, and it can reach the point of 00 meters, which is used for backbone or inter-building connection. But it should be clarified that due to the continuous advancement of network technology and the speed that this cable public can provide, the connection between backbones or buildings is gradually being replaced by faster optical fibers.
Nowadays, you can easily buy a coaxial cable that has been manufactured from a computer accessory vendor. You can also start manufacturing by yourself, mainly based on the following thinking:
(1) Further reduce costs;
(2) Need to adjust the length of the cable as
desired ; (3) I hope to start manufacturing the
fiber optic cable with glass as the main material. Light is used to transmit signals, and its physical structure is shown in the figure. 
In practical use, optical fibers are often bundled into optical cables to facilitate use. It is composed of the above parts:
skin: it is located in the innermost part of the optical cable, and holds a bundle of optical fibers together, which plays a better role in optical fiber maintenance;
core: each optical fiber is composed of a very thin glass filament, It is the medium for data transmission;
cladding: a layer of cladding glass is wound on the outer layer of the core of each optical fiber—the thin bevel glass. The density of this cladding is different from the density of the core, which can form the entire light. Reflection, the actual situation is the mode of optical fiber transmission.
The functional characteristics of
optical fiber The optical fiber is completely different from the cable introduced later. It no longer uses electronic signals to transmit data, but uses optical pulses to transmit and transmit signals. It is this special material that makes it have the incomparable advantages of cables:
extremely wide frequency band: it has an extremely wide frequency range, measured in GB bits;
Strong anti-interference: Since the light beam is transmitted in the optical fiber, the light beam will not be affected by external electromagnetic interference;
strong confidentiality: Since the light beam is transmitted, it will not radiate signals outward, effectively avoiding eavesdropping;
transmission ; Fast speed: optical fiber is the fastest transmission medium so far, and it can be easily reached;
long transmission interval: its main reduction is extremely small, and it is a constant in a large range, which is almost negligible in many situations. In this respect, it is much better than cables.
Multi-mode fiber and single-transverse fiber
Optical fiber is divided into single-mode fiber and multi-mode fiber;
single-mode fiber uses narrow core wire and uses laser as the light source, so its ground dispersion is very small; in addition, the laser is emitted into the fiber in one direction. And there is only one bundle, and the signal is relatively strong, and it can be used in high-speed, long-distance applications, and its cost is absolutely higher.
Multimode fiber is more commonly used in short-distance or lower relative speeds. It uses LEDs as the light source and uses a wide core wire, so its dispersion is large. In addition, there are multiple angles in the entire fiber. The incoming light, so its signal is not as good as single-mode fiber, but the absolute low price is its advantage.
In use, you can comprehensively think about the above situation and make a choice that conforms to practice. Microwave Microwaves
beyond the frequency range used by radio can also be used to transmit various data signals. Although microwaves are also a kind of radio waves in the final analysis, their missions are completely different, so they are included in a special category here.