Crosstalk and Integrated Wiring

With the development of science and technology, the computer price is getting lower and lower, the performance is getting better and better, the transmission speed of LAN is getting faster and faster, and the transmission medium of LAN is also switched from coaxial cable to twisted pair wires and optical fiber, twisted Pair wires have evolved from CAT1, CAT3, and CAT5 to CAT5E, CAT6, CAT6A, and CAT7.

Although the performance of twisted pair wires has been continuously improved, a parameter has always been accompanied by twisted pair wires like a ghost, and with the development of twisted pair wires, this parameter is becoming more and more important. This parameter is ------- Crosstalk (Crosstalk ).

Crosstalk may be the most important factor affecting data transmission at high speed. It is an undesirable energy value generated by a signal coupling to another signal. According to Maxwell's law, as long as there is a current, there will be a magnetic field, and the interference between the magnetic fields is the source of crosstalk. This inductive signal may cause data transmission loss and transmission errors. Therefore, crosstalk is undoubtedly the most powerful natural enemy for integrated wiring.

The difference between CAT1, CAT3, CAT5, CAT5E, CAT6, CAT6A, and CAT7 is that the copper wire diameter is getting thicker and thicker, the torque is getting smaller and smaller, the twist of the two cables is getting tighter and the gap between the line pairs more and more cross skeleton, aluminum foil, pull, streamline, copper wire woven mesh) the frequency ranges from 16 MHz to 100 MHz, 250 MHz, 500 MHz, and MHz, but the crosstalk also changes from the NEXT, PSNEXT, FEXT, ELFEXT, and PSNEXT between line pairs. to ANEXT and PSANEXT between cables, these are extensions of crosstalk and the expression of crosstalk.

In the crosstalk test, the high test value dB is better than the low test value. Because the crosstalk value is the ratio between a useful signal and a noise signal. A high test value means that the useful signal is much greater than the noise. A low test value means that the difference between the useful signal and the noise is not great. For the receiver, the signal cannot be correctly received, resulting in packet loss. Crosstalk is related to the frequency. When the frequency increases, the Crosstalk value decreases, which increases the copper wire diameter, increases the cable torque, and increases the cross skeleton to separate the cables, various production processes, such as increasing the thickness of the outer sheath or shielding layer, are used to solve the increasingly tricky crosstalk problem.

Transient crosstalk NEXT). This crosstalk is caused when the signal transmitted by the device on the sending end is coupled to the adjacent receiving end of another pair of lines. This is the most important crosstalk with a transmission rate smaller than Mbps. However, as the data transmission rate increases, all wired pairs of twisted pair wires need to transmit data in parallel transmission mode. The LAN system is also affected by other crosstalk-remote crosstalk FEXT) and equivalent remote crosstalk interference ELFEXT ). Remote crosstalk (FEXT) refers to the signal that is generated and sensed to the remote connection due to the signal from the end of the cable link to another line. ELFEXT is derived from attenuation and FEXT subtraction. Compared with FEXT, ELFEXT is more practical, because FEXT will definitely change with the length, which means that the same cable is in different lengths, the FEXT value is different, which cannot be used to measure the quality of the cable. However, ELFEXT introduces the attenuation parameter, which makes the cable test more practical, therefore, the ELFEXT parameter rather than the FEXT parameter often appears in the test report.

As the transmission rate increases, for example, in the hot 802.3an Standard 10G Base-T, the high frequency of MHz makes interference between cables that can be ignored previously, and is also considered, this is the external crosstalk ANEXTAlien crosstalk). If this parameter is unqualified, the rate of 10 Gbit/s will be greatly reduced, or even unable to run. CAT7 gives up the unshielded structure directly, and uses a single shielding Method for copper wire shielding to solve the interference between the inside of the cable and between the outside of the cable. I have to say that, crosstalk makes the cable structure more and more complex.