Currently, many places use twisted pairs when doing network projects. Due to cost and construction complexity, optical fiber is mainly used for backbone networks. "Fiber to the desktop" will probably take some time. Coaxial Cable has largely been phased out. Twisted pairs are divided into two categories: shielded twisted pairs (STP) and unshielded twisted pairs (UTP). STP is only used in some special occasions (such as severe electromagnetic interference, susceptible to corrosion by chemicals, etc.). The most popular one is UTP. Judging from the author's actual experience, there are more fake twisted pairs (using other people's trademarks) on the market than real ones, and the fake ones also have the same marks as the real ones. In addition to fake wires, there are many cases in the market where Category 3 wires are used to impersonate Category 5 wires and Category 5e wires, so it is necessary to explore the identification methods of network cables.

First of all, let’s determine whether it is a fake foreign manufacturer. Domestic system integrators generally use foreign network cables. The reason is that the quality of foreign network cables is indeed much better than that of most domestic network cables, and projects are easier to pass inspection. Therefore, some unscrupulous domestic manufacturers have begun to imitate foreign network cables. . How to tell whether a network cable is counterfeit? An IT technician inspecting goods at the customs said an inspection method: the plastic skin on the outside of foreign network cables is very elastic. If you fold a section of the network cable in half, if it can spring back immediately, you can basically think that the network cable is genuine (note: it cannot Fully guaranteed).

Then determine the type of twisted pair. The conductors in twisted pair cables appear in pairs, with every 2 wires forming a pair, and are twisted around each other. According to the American Wire and Cable Specification (AWG): all wires in a twisted pair should be 4 pairs, with a maximum of 8 wires. However, the 10M Ethernet standard stipulates that only 2 pairs of wires are used to transmit signals, so some of the Category 3 twisted pairs are 2 pairs, and some are 4 pairs. The emergence of Fast Ethernet, on the one hand, theoretically increases the speed of the original 10M network by 10 times, on the other hand, it prepares for future faster networks (Gigabit Ethernet, transmission speed is 1000Mbps), and simultaneously transmits Category 5 twisted pair cable with a speed of 100Mbps is also put into use. While Fast Ethernet only uses 2 of the pairs, Gigabit Ethernet must use all 4 pairs. It is recommended that you read more about the markings on the network cables. If it is marked with "CAT3", it is generally Category 3 cable. When it is marked with "CAT5", it means Category 5 twisted pair cable. If it is marked with 5E, it is Category 5e.

It is also necessary to actually test its speed, because the phenomenon of "selling dog meat to a sheep's head" also exists in the network cable market. The networks currently established generally use Category 5 or above twisted pairs, and Category 3 twisted pairs have become obsolete products. However, after the introduction of the Category 5 twisted pair standard, some twisted pair manufacturers packaged the conductors originally used for Category 3 lines in cables with the words Category 5 twisted pair printed on them for sale. When you use this type of fake Category 5 cable, the actual communication speed of the network can only reach the 100Mbps specified by Category 5 twisted pair within a short distance. This kind of fraud is very hidden and difficult for ordinary users to detect. At this time, it is recommended that you purchase a section first and test it yourself using the "System Monitor" in Windows 95/98 or the "Network Monitor" in Windows NT Server 4.0. If the test speed reaches 100Mbps, it means that it is Category 5 twisted pair. If it is only 10Mbps, it means that Category 3 wires are used in the cable. This method can not only correctly distinguish between Category 3 wires and Category 5 wires, but can also be used to test whether the twist degree of each pair of conductors in a twisted pair cable meets the standard. It can also test whether the metal medium in the conductors is qualified. Please note: When conducting network speed tests, the length of the twisted pair should be the standard length of 100 meters, otherwise the measured data will have no practical significance.

Finally, you need to test whether the network cable has certain properties such as heat resistance, tensile strength, flame resistance, and flexibility: First, you can test the twisted pair in a high temperature environment to see if it is really double. When the ambient temperature of the twisted pair reaches 35°C to 40°C, the outer layer of rubber will not soften, but the fake one will; secondly, in order to ensure the safety of the connection, the outer rubber of the real twisted pair cable has a stronger Tensile resistance, but the fake one does not; thirdly, metallic copper is generally used in twisted pair cables, and some manufacturers add other metal elements to copper in order to reduce costs during production, which is intuitively adulterated. The last wire is obviously harder than the normal one, not easy to bend, and is prone to breakage during use; fourthly, the rubber on the outside of the real twisted pair is also flame-resistant, while the fake ones are made of ordinary flammable materials. You can try it yourself when purchasing.

How to choose the appropriate network cable

First, let’s talk about whether to use STP or UTP. This issue is relatively complex and is also a long-term dispute among manufacturers. Because it is difficult to clarify under what circumstances shielding should be used and under what circumstances non-shielding should be used. Later, a domestic authoritative organization determined a principle, mainly based on the electromagnetic interference field strength existing in the area where the integrated wiring is located to determine whether to use STP. This indicator is 3 volts per meter. If it is lower than 3 volts per meter, unshielded wires can be used. Otherwise, shielded wires should be used, or shielding measures or optical fibers should be used. Laying the cables in metal steel pipes or trunking and ensuring grounding, or increasing the distance between the cables and interference sources can all play a shielding role. In fact, in engineering, the interference field strength is rarely greater than 3 volts per meter. It can be said that 90% of the cases are less than 3 volts per meter. Therefore, it is not recommended that you blindly choose a shielding system, but should proceed from the actual situation. Because even if the voltage is higher than 3 volts per meter, taking certain shielding measures can reduce the impact of interference sources. Besides, the test standards and test instruments for testing the shielding effect of shielded wiring projects have not yet been solved. The use of shielding systems will naturally increase the project cost a lot.

Finally, let’s talk about whether to use Category 6 or optical fiber for Gigabit Ethernet. If the network is 100M, Category 5 and Category 5e are the only choices. There is no need to use Category 6 or optical fiber. If the network is 1000M, should 5E, Category 6 or optical fiber be used? There have been many articles recommending the use of Category 6 cables, but the author disagrees, because first, the connection structure of Category 6 cables has not changed. It is the same as Category 5e cables, but it is different from the currently widely used plug module (RJ45). Completely incompatible; although the Category 6 cable rate in No. 2 Middle School can reach 200M to 250M, the construction cost is much higher and the construction difficulty is also relatively high. Besides, the current price of optical fiber has basically reached a stage that users can afford. Therefore, for enterprises with high bandwidth requirements and abundant funds, it is recommended to choose fiber-to-desktop cabling; enterprises with insufficient funds basically use 5E on Gigabit Ethernet. That's enough.

Nowadays, the development of wiring technology is basically a new hot spot appearing in half a year, but I think the development of cables must have a limit. The development of cables that use twisted pair principles to transmit signals has almost reached Category 6. The end. With the development and widespread application of optical fiber technology, its price has shown a downward trend. In addition, optical fiber has anti-interference, security, high bandwidth and other advantages that cables cannot match, making it closer and closer to users. In the past, only trunk lines used optical fiber. Compared with the situation, optical fiber has now been laid to buildings and may be directly delivered to homes in the future. Its development prospects are bright. As for Category 6 copper wires, they are expensive (for the entire system, not just the twisted pair itself), and the installation process is complex, requiring high engineering maintenance, making it inconvenient for widespread use, and it is even less likely that copper wires will be universally used. The end of , 5E is most likely the end. Because the structure of Category 6 products is different from current wiring products, there is a reverse compatibility problem, and they are all shielded products, which will bring certain difficulties to engineering construction. If optical fibers and optical/electrical switching devices develop according to current trends and costs further decrease, perhaps Category 6 products will become transitional products like Category 4 products. Cabling manufacturers are promoting Gigabit cabling products: one is "5E"; the other is "Category 6". When choosing a product, you should calmly consider which cabling system to choose. The final result is still determined by the application.

At present, Gigabit Ethernet is mainly used as the network backbone. It is difficult to say when it will be truly used for horizontal subsystems on the desktop. I am afraid that by then, the situation of what products to use will have changed.

Because copper cable will eventually be unable to exceed its own bandwidth, transmission distance and electromagnetic interference limitations, its replacement will still be optical fiber, or some future transmission medium.