Alien crosstalk (AXT) is electromagnetic noise that can occur in a cable that runs alongside one or more other signal-carrying cables. The term "alien" arises from the fact that this form of crosstalk occurs between different cables in a group or bundle, rather than between individual wires or circuits within a single cable. Alien crosstalk can be particularly troublesome because, unlike the simple crosstalk caused by a single interfering signal, it cannot be eliminated by phase cancellation. Alien crosstalk arises from multiple signals, and includes mixing products in which phantom signals at innumerable sum and difference frequencies blend with the originating signals. The result is a "hash" of electromagnetic noise that is too complex to be dealt with by phase-cancellation measures. Because it resembles noise rather than signals, alien crosstalk degrades the performance of a communications system by reducing the signal-to-noise ratio (S/N). Alien crosstalk can be minimized or eliminated by avoiding configurations in which cables are bundled together or run parallel to one another in close proximity. If cables must be run parallel to each other, each cable can be surrounded by a grounded metal braid (electromagnetic shield) to prevent electromagnetic fields from entering or leaving the cable. This in effect isolates the cables from one another. However, it is an expensive solution and it can also increase cable loss per unit length