Twisted pair purchase knowledge

The network cable is the basis of the entire network, and it can be ambiguous at all. So how can we choose a twisted pair?

Understand the basics of twisted pair

The twisted pair is composed of four sets of copper wires entangled with each other and encapsulated in a layer of insulating jacket. The reason why they are entangled is because when a current (in fact, a data stream) passes through the metal wire, an electromagnetic field is generated, and the positive and negative signal lines are wound, and the positive and negative magnetic fields generated by the two cancel each other. To reduce signal interference.

Twisted pair is divided into two categories: UTP (unshielded twisted pair) and STP (shielded twisted pair). The difference between them is that there is a layer of metal between the copper wire and the outer insulating sheath of the STP to reduce the electromagnetic radiation of the signal to prevent it from being monitored, while UTP is not, the electromagnetic radiation is relatively large, and the probability of being monitored is also A lot higher. The theoretical speed of STP can reach 155 Mbps in speed, while the theoretical speed of UTP is only 100 Mbps. The price of STP is much more expensive than UTP, and it has high requirements for other network equipment and wiring. Therefore, it is generally only used in local area networks where transmission quality and confidentiality are required. In most local area networks, UTP is basically used.

In addition to the above classification, twisted pairs are also classified by "class". At present, the most commonly used are the Category 5 and Super 5 lines with a theoretical transmission speed of 100 Mbps. At the same time, with the advent of the Gigabit network, the corresponding Category 6 lines have gradually entered the market. However, there are still some profiteers in the market who sell Category 3 lines with a transmission speed of only 10 Mbps and Category 4 lines of 16 Mbps as Category 5 lines, so users must be vigilant.

Seeing is believing, picking twisted pair on the spot

As the saying goes, listening to the ear is virtual, seeing is believing, after understanding the basic knowledge of the twisted pair, the next step should enter the actual phase of the twisted pair.

Choose from appearance features

It should be said that to determine the quality of the twisted pair, the most direct way is to conduct a practical test, but if you buy a small amount, the business will not let you do the test, and then test to do a lot of preparation, maybe you I will feel annoyed myself. Then in this case, we may wish to pass the identification of the appearance of the twisted pair. Although a product with a good appearance is not necessarily excellent in performance, but the shape is shoddy, the performance is certainly not good.

Look at the logo, clear categories

Generally speaking, there are some product identifications on the insulated outer sheath of the twisted pair. The main products are the brand and product category. For example, the label is AMP CAT5UTP, which means that the product is AMP brand five unshielded double. Stranded wire, if labeled as CAT4, is represented as a four-category line. Of course, some JS will refill the original logo by replacing the original logo with a new one. However, in general, there will be some clues. Even if you can't see it from the appearance logo, you can pass the following Aspect to identify.

Flexibility, indicating the pros and cons of materials

Since the twisted pair is made of a copper material, the flexibility of the copper is relatively good, it is easy to bend but is not easily broken, and it is very easy to route. Therefore, it is advisable to take a twisted pair of wires repeatedly in the hand for more than ten times. Whether it is broken or too soft, and no metal texture indicates that the material of the product is problematic, the manufacturer incorporates other impurities into the copper in order to reduce the cost.

Quantity winding, inspection production process

As mentioned above, in order to eliminate the electromagnetic field, the twisted pair uses a method in which four pairs of wires are entangled. But different lines, their tasks in the network transmission are different, the frequency of the magnetic field is also different, so the degree of compaction of the four pairs of wires (called the winding) is also different. When purchasing, we may wish to dial the outer wrap of a section of the line and check the winding distance. If the winding distance of the four pairs of wires is equal, there is a problem with the manufacturing process. Such a line cannot be resolutely; if you find that the winding distance is large, Especially if it is more than 10 cm, then this line must not be a Category 5 line.

Temperature resistance and flame retardancy ensure safety

In order to ensure the safety of the network, twisted pairs have certain requirements for temperature resistance and flame retardancy. In terms of temperature resistance, it is generally required that the skin of the foreskin does not occur at 45 degrees Celsius; in terms of flame retardancy, it is required that the foreskin is allowed to be melted under high temperature of open flame, but spontaneous combustion cannot occur. For these two properties, we can test by heating and using open flame points.

Extensible convenience wiring

In the process of wiring, the twisted pair is inevitably bent and twisted, so the twisted pair is required to have a certain extension to facilitate wiring. We can try to pull it by hand. If even our hands can break the foreskin of the twisted pair, then there is no doubt that this is a poor quality product.

Test on site

Of course, the most reliable way to quality the twisted pair is to conduct on-site testing. So how do we test it if conditions permit?

First of all, it needs to be clear that although the UTP of Category 5 and Category 5 can theoretically achieve a transmission speed of 100 Mbps, even the best products are unlikely to reach 100 Mbps due to the transmission delay of the line and the transmission delay of the equipment. The speed, able to reach more than 60Mbps has been a very good product. At the same time, as the length of the transmission line increases, the speed will also drop significantly.

In order to make the results of the test as far as possible reflect the real situation of the product, the bottleneck is reduced as much as possible in the test. Do not use inferior graphics cards on the hardware. The connection method should use the direct interconnection method of the two machines. The hard disk should use more than 7200 rpm products, especially if it is a SCSI hard disk. In software, the system should be clean, do not use too much debris, the best defragmentation before testing. The test can be performed by copying a large file of more than 100 MB. After counting with the stopwatch, the file size can be divided by the time used to obtain the test speed.

The length of the test line can be selected from several lengths of 5 meters, 10 meters, 30 meters, 50 meters or more, because these lengths represent different length levels. There are some inferior lines that perform very well below 10 meters, but the original shape is revealed from one to 30 meters.