When the link is too short, be careful about the crosstalk and ripple loss at the end.

In the design, construction, and acceptance of Integrated Wiring for Common Buildings, the length is often the most important issue. Due to the Inherent Resistance of the copper conductor, the transmission distance of the copper conductor cannot be too long. Therefore, the TIA organization has developed a link of up to 90 meters and a channel standard of up to 100 meters, more people are concerned about the possibility of transmitting copper cables farther away.

Few people are concerned about short links. As we all know, the longer the copper cable length, the lower the test parameters and the worse the performance.Short link problems mean that the shorter the link, the lower the test parameters, and the lower the possibility of passing the test. In particular, when the link length is less than 15 meters, the performance of the two important parameters is decreased sharply.According to TIA/EIA standards, the "short link" is defined as a horizontal cable link less than or equal to 15 meters between connectors. Short link problems are defined as that when the horizontal cable distance between the two connectors is shorter than the standard, the NEXT and return loss effects of the second connector are not completely reduced.

During signal transmission, the signal will return a strong reflection signal when it encounters a local terminal connection module with Discontinuous characteristic impedance, and the cable is distorted and squashed. If the link is short and the strong reflection signal does not get enough attenuation, a strong echo signal will be detected at the signal sending end, and a large reflection signal may be regarded as the received signal, this effect will generate an error code, and the test will cause the Return Loss Test to fail. Just like when the water in the rough pipe enters the fine pipe, the water will flow back. The Standards Board noted this phenomenon, following the release of the 568B cat6 cabling standard by TIA, followed by the release of the TIA 568B. 2-3. In the appendix, the insertion loss and Return Loss of short links are revised to introduce the 3 dB principle. When the insertion loss of the link to be tested is less than 3 dB, the return loss performance can be ignored. This does not serve as a basis for determining whether the overall link performance passes through.

Near-end crosstalk NEXT) is another important parameter, which is a ratio between the received correct signal and the near-end crosstalk signal. In the process of signal transmission, high-frequency electronic clock causes strong mutual interference between signals. If the twisting distance is too large during the construction process, the test of the near-end crosstalk will fail. The NEXT signal generated at the Cosco end of the short link is not effectively reduced and transmitted to the nearest end, leading to test failure. ISO introduces the 4 dB principle in the ISO11801 standard, that is, when the inserted loss of the tested link is less than 4 dB, the NEXT performance can be ignored, and it is not used as a basis for determining whether the overall performance of the link passes through. This principle is applicable only to the ISO standard and not to the TIA standard.

There are few short links in a common building, but most of the cabling systems in the data center are short links. It can be seen that the problem of short links is also worth noting. You can solve short link problems through the following measures:

1. Avoid the occurrence of short links during design and construction. Try to make the link length longer than 15 meters, but it is not recommended to increase the link length.

2. prevent excessive cable distortion during construction and reject brutal construction.

3. Good module and distribution frame end connection.

4. promptly discover and solve problems during construction.

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