Cable purchasing for network cabling

I have been engaged in system integration for a long time and have a deep understanding of the importance of network cabling. According to authoritative statistics, more than 70% of network faults are caused by network wiring. I believe this sentence. It is believed that the counterparts engaged in system integration often encounter some "inexplicable" problems: when the network is disconnected; when the distance is a little longer (not more than 100 M ); 10 m is normal, M is not normal, the number of workstations is small, the task is not busy, and the use of five types of lines, the network speed is surprisingly slow, and so on, these problems are mostly caused by network wiring, I will discuss the problem of network cabling based on my practical experience.

Chaotic twisted pair wires "high standards"

On the market, there are three categories of twisted pair wires, four categories, five categories, over five categories, six categories, over six categories, and even seven categories, the technical indicators of these twisted pair wires are recognized as being from Category 3 to Category 5. Category 6, Category 6, and category 7 are basically self-styled by manufacturers. Because more than five categories of standards have already been introduced, some manufacturers have produced a type of technical indicator that is better than five categories, and 6 categories of Self-sealing; due to market competition, other manufacturers have produced a network cable that is higher than the "6 categories" Technical indicator, so it has to block itself into more than 6 categories. This is also true for the emergence of 7 categories.

In practice, category 3 and Category 4 do not exist in the market. Therefore, we will only discuss the Category 5 or more twisted pair standards in this article. Category 5 lines are mainly proposed for a m network. Of course, the 10 m network is more than enough. The working mode is basically half duplex, and the Standards of Category 5 lines are the most mature, it is also the mainstream in today's market. Later, when we developed Gigabit Ethernet, we planned to run it on Category 5 twisted pair wires. However, in practice, it is found that about 30% of the information points of the original 5 types of cabling products may fail the electrical performance test when supporting gigabit network applications, that is to say, not all five types of cables can run Gigabit Ethernet, which is mainly reflected in whether the electrical performance meets the requirements for full-duplex transmission of 4 pairs of cores required by Gigabit Ethernet, that is, starting from full-duplex transmission information, in the four-core cable, the NEXT and other indicators of different combinations of cables and cable pairs should comply with the specifications of the five types of cables, each line supports 400 MHz of bandwidth and 4 pairs of cores have a total of MHz of available bandwidth. The designed operating frequency of Gigabit Ethernet is MHz. When the twisted pair wires that meet the requirements of the existing five types of standards work in half duplex mode, only the two pairs have MHz available bandwidth. As a result, many vendors have pushed 5 categories of products that can run Gigabit Ethernet to the market with "Enhanced" (Enhanced Cat 5, 5E). The U. S. TIA/EIA 568A-5 is 5E standard, "5E" is also known as "over 5 categories", which is the origin of 5E.

Later, there were 6 categories, 6 categories, and even 7 categories, which are mainly related to the development of computer networks. According to Moore's Law, information requirements on computer networks are doubled every 18 months. Computer Networks are evolving to Gigabit Ethernet, the Application Requirements for the comprehensive cabling system are 4 pairs of twisted pair wires in full duplex mode, which is the background of the emergence of cat5e and cat6 cables. For the 6 categories of cables, the international standards have not been finalized to determine whether it is set to 250 MHz or MHz, but the manufacturers have already produced with MHz as the indicator, therefore, using six types of lines to run Gigabit Ethernet is not a problem. According to the existing technical indicators, there are indeed more than five category 6 lines, but the category 6 lines may not be popular. On the one hand, there is no unified standard and there is no "explicit confirmation "; on the other hand, it has a strong rival-optical fiber. With the increasingly mature optical fiber technology, the performance is getting higher and higher, and the price is getting cheaper and cheaper, the cat6 lines are likely to disappear in the market, not to mention cat6 and cat6 lines; third, other cabling devices supporting Category 6 cables are incompatible with existing category 5 and Category 5. All of this may lead to 6 categories of "getting out of the game before getting ready ".

How to identify true and false twisted pair wires

At present, there are many areas where twisted pair wires are used in network engineering. Due to the cost and construction complexity, the optical fiber is mainly used for the backbone network. I am afraid it will take some time to get the fiber to the desktop, the coaxial cable has been basically eliminated. Twisted Pair wires are divided into two types: Shielded twisted pair wires (STP) and unshielded twisted pair wires (UTP). STP is only used in some special cases (such as serious electromagnetic interference and chemical corrosion, UTP is the most used. From the actual experience of the author, there are more fake twisted pair wires (using others' trademarks) on the market, and the fake line also has the same mark as the real line. In addition to fake lines, there are many situations where three types of lines are used to pretend to be five-category lines and cat-5e lines, so it is necessary to discuss the network cable identification method.

First, identify whether it is a fake foreign manufacturer. Generally, system integrators in China use mostly foreign network cables, because the quality of foreign network cables is indeed much better than that of most domestic network cables, and the project is easy to pass acceptance, so some illegal manufacturers in China began to copy foreign network cables. How can I sign off if the network cable is fake? An IT technician who inspected the goods at the Customs said a method of inspection: the plastic skin outside the foreign network cable is very elastic, and a piece of network cable is folded in turn. If it can bounce back immediately, basically, this network cable is considered genuine (Note: it cannot be completely guaranteed :)).

Then determine the type of the twisted pair. The wires in the twisted pair cables are paired, and each two wires is a pair and twisted. According to the U. S. Cable specification (AWG): All wires in twisted pair wires should be 4 pairs, a total of 8. However, the 10 M Ethernet standard requires only two pairs of wire transmission signals, so some of the three types of twisted pair wires are two pairs, while some are four pairs. The emergence of Fast Ethernet improves the speed of the original 10 m network by 10 times theoretically, and prepares for a faster Network (Gigabit Ethernet with a transmission speed of 1000 Mbps) in the future, 5 category twisted pair wires with a transmission speed of Mbps are also in use. Although Fast Ethernet only uses 2 pairs, all 4 pairs must be used for Gigabit Ethernet. We recommend that you check the online tags. For example, the tags marked with "CAT3" are generally three types of lines, when the words marked with "CAT5" are described as 5 category twisted pair wires and 5 category E.

Finally, we need to test its speed, because the phenomenon of "selling dog meat with goat heads" also exists in the network cable market. Currently, more than five types of twisted pair wires are used in the network, and three types of twisted pair wires are already obsolete products. However, some twisted pair cable manufacturers have launched the category-5 twisted pair standard, and then sold the wires originally used for category-3 wires in cables printed with category-5 twisted pair wires. When you use this type of fake five lines, the actual network communication speed can only reach the 100 Mbps specified by Category 5 twisted pair wires within a very short distance. This kind of fraud is very concealed and hard to be discovered by users. At this time, we recommend that you purchase a segment and use "system monitor" in Windows95/98 or "network monitor" in WindowsNTServer4.0 to test it yourself. If the test speed reaches 100 Mbps, it indicates that it is a category 5 twisted pair. If it is only 10 Mbps, it indicates that the cables use three types of wires. This method not only correctly distinguishes between Category 3 and Category 5 cables, but also can be used to test whether the twisting degree of each pair of wires in a twisted pair Cable conforms to the standard, it can also determine whether the metal medium in the wire is qualified. Note: During the network speed test, the length of twisted pair wires should be 100 M. Otherwise, the measured data has no practical significance.

Finally, you need to test whether the network cable has a certain heat resistance, tensile strength, fire resistance, bending and other performance: First, you can put the twisted pair wires in a high temperature environment to test, when the surrounding temperature of twisted pair wires reaches 35 ℃ to 40 ℃, the outer layer of the tape won't become soft, but false will; second, in order to ensure the connection security, the outer rubber of twisted pair cables has strong tensile strength, but not false. Third, copper is generally used in twisted pair cables, and some manufacturers in order to reduce costs during production, other metal elements are added to copper, which indicates that the line after blending is much harder than the normal one, which is not easy to bend and is prone to disconnection during use; fourth, the outer rubber of the twisted pair wires is also resistant to fire, while the fake one is made of ordinary flammable materials. You can try it yourself when buying it.

How to select an appropriate network cable

First, let's talk about whether STPS or UTP is used. This issue is complicated and is also a long-term controversial issue between manufacturers. It is difficult to specify the circumstances in which a block is used. Later, an authority in China decided to determine whether to use STP Based on the electromagnetic interference field in the region where the Integrated Wiring is located. This indicator is 3 volts per meter. If the value is less than 3 volts per meter, non-shielded cables are optional. Otherwise, screen cables are used, or measures or optical fibers are used. Place the cable cloth in a metal steel pipe or cable trough and ensure grounding, or increase the distance between the cable and the interference source, can play a shielding effect. In practice, there are very few cases where the interference field intensity is greater than 3 volts per meter. It can be said that 90% of the cases are lower than 3 volts per meter. Therefore, we do not recommend that you choose to block the system blindly, but proceed from the actual situation. Even if it is higher than 3 volts per meter, some shielding measures can also reduce the impact of interference sources. Besides, the test standards and instruments for the Shielding Effect Test of the shielded wiring project have not yet been solved. The use of the shielding system will naturally increase the engineering cost a lot.

Finally, let's talk about whether to use 6 categories or optical fiber over Gigabit Ethernet. If the network is m, category 5 and Category 5 are the best choice, and there is no need to use category 6 or optical fiber. If the network is m, is 5E, 6, or optical fiber used? Many articles have suggested six types of cables, but I do not agree, because the connection structure of the six types of cables is not changed, just like that of the five types of cables, however, it is completely incompatible with the widely used plug-in Module (RJ45). Although the speed of the six types of cables in No. 2 middle school can reach 250 M to M, the construction cost is much higher and the construction difficulty is also relatively high. Besides, the current price of optical fiber is basically at the end of what users can afford. Therefore, for enterprises with high bandwidth requirements and ample funds, it is recommended to select optical fiber cables for desktop cabling; it is enough for companies with insufficient funds to use 5E over Gigabit Ethernet.

Now the development of Cabling Technology is basically a new hot spot in the past six months, but I think there must be a limit to the development of cabling, the cable that uses the twisted pair principle to transmit signals has almost reached the end of category 6. With the development and wide application of optical fiber technology, its price has declined. In addition, optical fiber has advantages such as the incomparable anti-interference, security, and high bandwidth of cables, making it closer to users, compared with the previous situation where optical fiber is used only for trunk lines, the optical fiber has been laid to the building and may be directly delivered to the household in the future. Its development prospects are bright. As for the cat6 copper wires, they are expensive (for the whole system, rather than the twisted pair wires itself), and the installation process is complicated, which requires high engineering maintenance and is inconvenient to be widely used, more likely, it will be the end of the widespread application of copper wires. 5E is most likely the end. Because the structure of the six types of products is different from that of the existing wiring products, there is a problem of reverse compatibility, and all products are shielded, which will bring some difficulties to the project construction. If optical fiber and optical/electrical adapters develop in accordance with the existing trend and the cost is further reduced, Category 6 Products may become transitional products like Category 4 products. Cabling manufacturers also promote Gigabit cabling products: "5E" and "6 categories ". When selecting a product, you must calmly consider which cabling system to choose. The final result is determined by the application. At present, Gigabit Ethernet is mainly used as the backbone network. It is hard to say when it is actually used for the horizontal subsystem to the desktop. At that time, I am afraid the usage of what products have changed. Because copper cannot surpass its own bandwidth, transmission distance and electromagnetic interference restrictions, it will still be replaced by optical fiber, or a certain transmission medium in the future.

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