Network Cabling Basics: NET wire knowledge full contact

In multimedia, a variety of audio and video technology is widely used today, users of the network requirements are more and more high, the amount of data transmission has become more and more big. In this environment, as the bearer of data transmission-transmission media become more important, when the network construction enterprises, network cabling needs to build a strong performance and safe and effective foundation. Therefore, in the network cabling, understand a variety of network transmission media is very important, today I will take you to fully understand the network transmission media (Wired media).

In the computer network wiring, can be divided into wired media and wireless media two kinds, and the cable medium is the computer network most main transmission medium, usually divides into the copper medium (twisted pair and coaxial cable) and the optical medium two kinds, the wireless medium as the effective supplement of the wired medium, is widely applied in the network which does not fit the wiring. Let's take a look at these wired transport media.

Copper Medium:

Copper medium is a kind of electric signal transmission medium which is widely used in computer network, there are two main twisted-pair and coaxial cable, now the newly built computer network is basically a twisted pair as the transmission medium Star topology network, and coaxial cable is gradually out of the computer network market, Currently the most widely used scene is the cable TV network that we are familiar with, and cable TV connection cable in home is fine coaxial cable.

1, twisted-pair wire (Twisted-pair cable)

Twisted pair is one of the most widely used media in the star topology of computer networks, consisting of eight copper conductors in order to reduce the mutual interference of electromagnetic signals, each two of them are twisted together in a certain density. In this way, the transmission of electrical signals between each other, the radio waves will cancel each other, effectively eliminating interference. Twisted pair The name is also because of this structure and lead out. On the outside, there is a layer of toughness and high protective skin protection. ---http://bianceng.cn (computer science)

Shielded twisted pair Wire
According to its twisted-pair cable whether there is a shielding layer, we can divide the twisted pair into shielded twisted pair and unshielded twisted pair of two kinds, in the distinction of time, you can visually to see whether there are aluminum tin package in the outer protection sleeve. Basically we will choose unshielded twisted pair when wiring, the biggest reason is because this kind of twisted-pair line is much easier than shielded twisted-pair line in making craft. From the safety point of view, shielded twisted pair of twisted-pair cable has a higher ability to prevent the interception than the unshielded UTP, the transmission performance is better than the unshielded twisted pair.

Non-shielded twisted-pair wire
The first use of twisted pair was used for telephone signal transmission, which was gradually introduced into digital signal transmission, in a long time ago, we are basically using the 3-type twisted pair, the maximum can reach 16Mbps of bandwidth, and now we are widely used in computer networks are super five-type twisted-pair and six-type twisted-pair line. Up to 1000Mbps of bandwidth.

Usually we're all RJ45 connectors, it is commonly known as the Crystal Head to connect the twisted pair and network port, which in the use of only eight of the core of 4, for two-way transmission (Full-duplex), according to the network port connection at both ends, there will be straight line, crossover line and rollover three species, The straight line is mainly used for different two ports, such as network card-switch, the crossover line is used to connect the same two ports, such as network card-network card, and the rollover line is mainly used to connect the switch or the router's control port using the RJ45 converter.
　
Straight line

Cross Line

Rollover Line
Twisted pair of the only drawback is that the transmission distance is shorter, can only reach 100 meters, so in the wiring, if the use of star topology structure, covering the range can only reach 200*200 meters.

2, coaxial cable

The other kind of copper medium is coaxial cable, this cable is different from the twisted pair, only one of the internal copper wire for transmission signal purposes, in the copper conductor and protective coat between the shielding layer, different coaxial cable shielding layer is not the same, such as in the baseband coaxial cable, shielding is usually copper material network, The wide-band coaxial cable uses aluminum-shaped stamping technology materials. All these make the copper shaft cable have higher shielding performance and better anti-interference ability than twisted pair wires. Because there is only one copper wire inside the coaxial cable, all of the equipment must be connected to this wire using the BNC connector, which is what we often call the general linear physical topology.

Coaxial cable internal structure
In the network of the total line topology, the signal is sent from the sending machine to both ends of the cable, so there is a need for grounding at the end of the structure. By using grounding, the signal is not reflected back to the cable. If the grounding is not installed, the cable will produce duplicate electrical signals, submerged normal signal.
　
BNC connector

There are two main coaxial cables, coarse coaxial cable and fine coaxial cable, thick coaxial cable is the longest transmission distance in the copper medium, in the standard of 10BASE5, can reach 500 meters of transmission distance. The fine coaxial cable can transmit 185 meters in the standard of 10BASE2.

At present, coaxial cable in the computer network application has been very little, with the supporting equipment is less and fewer, the main reason is because of its production process than twisted twisted pair, and the overall linear topology of the computer network, all the computers are chained to a piece of media, any point of problems may cause the whole network paralysis. So copper-axis cables are now basically only used in cable TV networks, and the cable cables we usually see are fine coaxial cables. The last time I saw it. The application of coaxial cable in the computer network is 2002, when it is mainly because the transmission distance over the twisted pair of 100 meters limit, and only two or three machines, there is no need to connect fiber. Only in this case will we consider applying coaxial cables to the computer network.

Optical media:

Optical fiber Because of the use of light signals, in the transmission distance, data load and signal anti-jamming performance and so on, there are incomparable advantages, but because of its cost is still relatively high, its application or stay in the backbone network and long-distance network, fiber to the desktop is still unreachable things.

From the optical fiber structure, the basic consists of three parts of the external protective layer, the internal coating layer and the core composition of the fiber. The external protective layer is mainly designed to protect the interior of the fiber, usually made of very hard materials, the internal coating is mainly to prevent the leakage of light signals. In the core of the optical fiber, is the main part of the transmission of light signals, are generally made of quartz glass, cross-sectional area is very small, fiber core diameter is generally designed to be 62.5 microns or 150 microns. There is no external protective layer and the internal coating of the fiber, we call the bare fiber, fiber jumper is a kind of bare fiber.

Fiber internal structure According to the different classifications, the fiber is usually divided into multimode fiber and single-mode fiber or step fiber and gradient fiber, the latter because of the optical theory, the reader will be more difficult to understand. So here we introduce multimode fiber and single-mode fiber.
　
Multimode Fiber and Single-mode fiber The core cross-section of multimode fiber is much wider than that of single-mode fiber, and the optical signal can be transmitted from different angles into the core of the fiber. As we can see from the image below, the optical signals can be transmitted in different modes, can be transmitted in a straight line, and the signal can be transmitted forward using refraction and reflection. Because of the different transmission modes of the signals, the time of the optical signals entering the optical fiber will also be different, and the possibility of the light dispersion is also greater because of the transmitting of many sets of signals on one channel. Multimode fiber In the initial application of more, now the application has been very few.

Single-mode Fiber core cross-section is usually very narrow, only one optical signal transmission, because only the use of separate mode of light signal, so in single-mode fiber, no light signal dispersion, which makes the transmission signal distance will be longer, the transmission of data is also higher.

In order to facilitate the reader to understand, we simply make a metaphor: you can think of multimode fiber is a very wide road (Fiber mode section width), on this road, cars, road cars and trucks can be used, but because of different models (different signal modes), the time to reach the destination is different. and Single-mode fiber can be thought of as a railway, although only one train at the same time, the speed is higher than the highway.
　
Full duplex transmission of two fiber A fiber is generally only one-way transmission signal, so if you want to form a full-duplex system, you must have two of fiber composition. Optical signal transmission is actually a variant of the transmission of electrical signals. The complete optical fiber communication system will have a light signal to the electrical signals and electrical signals to the light signal conversion process, this process by the photoelectric converter to complete.

The composition of optical fiber communication system In optical fibers, there is usually a need to have connectors to connect the fiber transmitter and receiver, usually we can buy in the market with the SC Connector with multimode fiber and the ST connector connected with Single-mode fiber.

St and SC connectors
Summarize:

Through the above understanding, we should have some understanding of the cable network transmission media, in the network wiring, only understand these, can according to their own needs to build a safe and reliable computer network. One of the most difficult to understand should be optical fiber media, if you have any in the optical fiber does not understand the place, can be in the IT168 of the network Management Club, we will provide readers with a comprehensive solution!