The difference and application of shielding and non-shielded twisted pair

In order to be able to adapt to the development of network technology, ISO/IEC has developed a series of wiring standards, the ISO11801 standard defines 5 types of cable bandwidth is 100MHz, the revised standard is discussed in the definition of 6 types of cable bandwidth is 200MHz, The bandwidth of the 7-type cable is 600MHz.

It should be noted that the bandwidth (MHz) of the cable and the rate of data transmitted on the cable (Mbps) are two distinct concepts. Mbps measures the number of bits that the line transmits in a unit of time; and MHz is measured in the unit time of the electronic signal oscillation times, for the 5-type twisted pair, its bandwidth of 100MHz, therefore, any application of the 5-class line of the network system should be less than 100MHz signal to transmit data, Can be more stable and reliable.

The coding method in the network system establishes the link between the bandwidth and the rate, and the excellent coding scheme can transmit the data at a high speed with limited bandwidth. A few years ago, IEEE used a code called CAP64 to carry out 622Mbps data transfer experiments on 5 pairs of twisted-pair wires. The precursor bit Ethernet 1000base-t is being developed, and is based on 5 types of cables to transmit 1000Mbps of data.

However, when the signal is transmitted at a high frequency on the line, if you do not take certain measures, will still be due to external electromagnetic interference and cable internal crosstalk generated a large number of transmission errors, so as to reduce the performance of the system, as many network administrators do not want to run on the 3-class cable on the 10M network system, They found that the performance of 100M network systems on 5 unshielded twisted-pair cables was not as fast and reliable as they had imagined. So what happens when you use a shielded twisted pair? What about using 6 types of unshielded twisted pair? More Wonderful content: http://www.bianceng.cn/Network/zhbx/

IBM's La Gaude laboratory has conducted rigorous experiments on this issue, with the aim of comparing the transmission error rate of unshielded twisted pair and shielded twisted pair in real-world network systems with strong electrical and power lines. The network system uses ATM155 and keeps it working at a rate of 120Mbps. The experiment follows EN 801-4 standards, with IBM's SFTP and UTP 5 Systems and another manufacturer's UTP6 class system

When the intensity of the alternating signal generated by the jamming source increases from 200V to 3500V, no error occurs in the data signals transmitted in the SFTP 5 class system. In a 5-class UTP system, the situation is not so good: when the voltage rises to 200V, the UTP system begins to produce data errors and loss. In practical application, the cable is often laid close to the strong wire cable, and the 220V alternating current in the power line becomes an important interference source affecting the performance of the wiring system. The test results are shown in table 1.

Table 1 UTP5, UTP 6, SFTP 5 test results

When network devices discover errors in the transmission process, they spend a significant amount of time on the retransmission and recovery of these erroneous data, which can greatly affect the actual available traffic, which confirms the concerns of those network administrators.

Because of the improvement of the performance of R J 4 5 plug (block) and the improvement of the signal-to-noise ratio of the cable, the transmission error rate of the 6 type of unshielded system is half lower than that of the 5 type system, but it still makes the network transmission speed greatly affected. It is proved that when the transmission of network system is more and more close to the bandwidth limit of the wiring system, it is more and more important to eliminate the electromagnetic interference from the external system.

To sum up, when the network cabling environment in the vicinity of strong electromagnetic field (such as power plants, substations, etc.), wiring system can be used to ensure the normal transmission of network information. According to the environmental electromagnetic interference, it is usually possible to adopt different shielding measures at three levels. In the case of general electromagnetic interference, metal bridge and pipe shielding methods can be used, that is, all the cables are closed in the pre-laid metal bridges and pipelines, and the metal bridge and pipe to maintain good grounding, so that the interference current can be imported into the earth, to achieve better shielding effect, but also can save a lot of money. In the presence of strong electromagnetic interference sources, shielded twisted pair and shielded connectors can be used to shield the system, and then auxiliary to Metal bridge and pipe, generally can also achieve better shielding effect. In the case of extremely strong electromagnetic interference, cable wiring can be used. The use of cable wiring is higher cost, but the best shielding effect, and can get very high bandwidth and transmission rate, using cable wiring network in 20 years to ensure its advanced, the network will not be eliminated by the wiring system behind.