Hello. This quick tutorial covers the near-end crosstalk and far-end crosstalk field testing parameters, two of several that must be verified to ensure standards compliance for the installed link or channel. Let's begin with the definition of crosstalk. Crosstalk measures the amount of signal sent over one pair in a cable that leaks, or is detected, on an adjacent pair. If there's too much leakage, it can affect signal integrity on the adjacent pair. When the measurement is at the signal source end, it's referred to as a near-end crosstalk or next test. And when it's performed at the other end of the link or channel, at the signal destination point, it's called a far-end crosstalk or FECS test. Since we're measuring the relative difference between the strength of a transmitted signal and the strength of its leakage, a higher decibel or dB value is better. It means there's more transmitted signal energy and less leaked energy. Let's take a closer look at the far end for a more detailed understanding of Fext. Fext will be greater on shorter links or channels than on longer ones because of attenuation or insertion loss, which reduces the strength of any signal over the length of a cabling run. In order to provide a test limit applicable to every possible link or channel length, the Fext value is adjusted for the attenuation measured on the link or channel. The resulting value is called the attenuation to crosstalk ratio, far-end, or ACRF. It should be noted that excessive crosstalk can be especially troublesome for applications that simultaneously transmit and receive over each of the four pairs in the cable, such as gigabit and multigigabit Ethernet networks. For this reason, modular or RJ45 ports on devices such as switches and network interface cards are designed with sophisticated crosstalk cancellation circuitry. Signal interference due to crosstalk will increase if proper installation practices are not followed, particularly at the termination points in the link or channel. As shown here, untwisting or separating the conductors in any pair makes it easier for signals to interfere with each other between that pair and the other adjacent pairs. We'll finish this module with a review of the published crosstalk limits for categories 5E, 6, 6A and 8. The applicable standard is the Telecommunications Industry Association or TIA 568.2-D, titled Balanced Twisted Pair Telecommunications Cabling and Components Standard. There are two sets of limits, one for maximum 100 meter end-to-end channels and the other for maximum 90 meter permanent links. The channel limits are lower because of the cords added at both ends. Note that category 5e, as shown here, is characterized to a maximum 100 MHz, with the dB values decreasing as the frequency increases. Recall that a higher dB value is better, since it means there's relatively more signal than leakage at the source or destination end. These values show that crosstalk becomes more of a problem at higher frequencies. Here are the limits for category 6, which is characterized to 250 MHz versus 100 MHz for Cat5e. The limits at a given frequency up to 100 MHz are higher for Cat6 than for Cat5e, due to the better performance of the cables, connectors, and cords. Next, we have the limits for augmented category 6 or Cat6A, which is characterized to 500MHz versus 250MHz for category 6. The limits shown here are the same as those seen previously for category 6 up to 250MHz, with additional values added to extend the characterization to 500MHz. And our last stop is category 8, which is a shielded-only cabling system characterized to 2000 MHz or 2 GHz, with a maximum channel length of 30 m instead of the usual 100, and a maximum permanent link length of 24 m instead of the usual 90. That's it, we're done. Thanks for watching.