Release date : 2016/9/5 10:16:27

1. Why can't you use the debugging of the network to test the performance of the cable?

At present, many users do not conduct certification tests on the installed twisted pair cables, but test them during the network debugging process. When the network can be connected, the installed cables are considered to be qualified. This approach is not only wrong but very dangerous. Because the network traffic is very low during network debugging, the user does not feel a problem at this time, but when the network traffic is high, it may be difficult to access the Internet. The fact that the network can be commissioned does not mean that the cable meets the installation standards, nor does it mean that the cable will work correctly when the network is running normally. In addition, at present, most users install Category 5 twisted pair cables, and the network running is 10Base-T, but 10Base-T can run does not mean that 100Base-TX can also run. Therefore, whether the installed cable can support high-speed signals must pass the relevant certification test to prove its performance. Otherwise, when the cable is upgraded to the high-speed network, it is found that there is a problem with the cable, and it is impossible or difficult to repair at this time.

2. What are verification tests and certification tests for cables?

The verification test of the cable is a general test to test the continuity, length of the cable, and whether the joint connection of the twisted pair is correct. Proof testing does not test the electrical specifications of the cable. The certification test is carried out according to an international cable standard. It includes the entire content of the verification test and the indicators of the standard test cable such as attenuation, characteristic impedance, etc. Verification testing does not guarantee that the installed cable can pass high-speed network digital signals, such as 10M or 10MHz. Only passing the certification test can guarantee that the installed cable can support 10M or 100M signal.

3. What are the standards or specifications for cable certification testing?

At present, the main international certification test standards for field installation cables are TIA 568A and ISO/IEC 11801. The former is mainly used in North America, and the latter is mainly used in Europe. In addition, some network standards also make some provisions for cables. However, the certification tests for cables installed in the field mainly use the above two cable standards. The main contents of the test standard (norm) include: the model of the cable link, the test method, the parameters (content) required to be tested, the test limit (the specific value or method of the parameter), and the requirements for the certification test instrument.

4. What is the TSB-67 standard?

Before 1995, the TIA 568A standard did not stipulate the Category 5 twisted pair (UTP5 or STP5) installed in the field. More and more users install a large number of Category 5 twisted pairs to meet the needs of high-speed networks. The TIA committee published the TSB-67 standard in October 1995, which is an appendix of the TIA 568A standard and is only applicable to the certification standard of the five types of twisted pair installed in the field. .

5. What are the characteristics of UTP cable and STP cable?

Many users today find it difficult to decide between installing UTP5 or STP5 cables. Many users only know that STP cables have better anti-interference than UTP cables. In fact, one of the main purposes of STP cables widely used in Europe is to prevent the signals transmitted in the cables from radiating to the outside and interfering with other electrical equipment. The price of UTP cable is cheaper than that of STP cable, the installation and maintenance are simple, and its anti-interference performance is not as good as that of STP cable. The price of STP cable is more expensive than UTP, and the requirements for installation and construction are higher, so the construction cost is more expensive than UTP, and the maintenance is not as simple as UTP. The anti-interference of STP is better than that of UTP, but the shielding layer of STP must be connected. If something goes wrong with the shield, such as a poor ground or an open circuit, the consequences are counterproductive. At present, there are no standards and methods for testing the effect of the shielding layer in the field, that is, the performance of the STP cable cannot be quantitatively stated in the field.

6. What is a cable link (Link)?

The so-called cable link refers to the connection of a cable, including cables, plugs, sockets or jumpers, couplers and so on. Different standards specify different links, that is, test models. For example, TSB-67 specifies Basic Link and Channel. It is particularly emphasized that the link is not equal to the cable, and the cable is only a part of the link. If the installed cable system is expected to support a bandwidth of 100MHz, the link should achieve this capability, not just the cable.

7. What is Category 5e twisted pair and its application?

Category 5e twisted pair is a twisted pair recently introduced by some cable manufacturers for use in local area networks. These manufacturers claim that the Cat5e cable can support signal transmission frequencies of 300MHz or higher. Whether these Cat5e lines can reach the frequency index claimed by their manufacturers aside, it is not the case at all in practical applications:

1. The highest transmission frequency of the current local area network does not exceed 100MHz, and the relatively new fast Ethernet such as 100Base-TX does not exceed the transmission frequency of 100MHz, so I have not seen its practical application in the near future.

Second, the cable is different from the link. The cable can reach a transmission frequency of 300MHz, but it does not mean that the link can also reach such a high frequency. Because the link is composed of cables, plugs, sockets and even couplers, wiring frames. If a Category 5e link is to be obtained, it must be ensured that all components in the link must meet the Category 5e standard. It is meaningless only if the cable is Category 5e and the link cannot reach Category 5e.

3. At present, there is no way to conduct on-site certification tests for the installed Category 5e links, which means that there is currently no standard to test the actual performance of these high-speed cables on-site. Since there is no way to check whether the installed cable can meet the performance of Category 5e, there is no way to fundamentally guarantee the actual investment.

8. What is Impedance Anomaly

Impedance is an electrical specification of the cable and should be a constant in the cable. If the impedance along the cable is not constant, reflections will occur where the impedance change occurs. Fluke's DS100 and DS2000 use a 15% reflection default value to report impedance anomalies, that is, if the reflected signal exceeds 15%, an impedance anomaly is reported. DSP100/2000 can draw the curve of characteristic impedance. The ideal curve should be a straight line. If the impedance is abnormal, there will be peaks or valleys in the curve. Peaks indicate an increase in impedance, and valleys indicate a decrease in impedance.