Alien Crosstalk Testing

BY: Christina Hansen


When installing 10 Gigabit Ethernet (GbE), an important part of the certification process is testing the network for the electromagnetic interference that can occur between wires or cables which are closely bundled together, otherwise known as Alien Crosstalk. Even though it may appear that Alien Crosstalk (AXT) testing can be a lengthy and frustrating project, there are ways of simplifying and speeding up the certification of your 10 GbE network.

The easiest way to pare down the amount of time spent on AXT testing is to divide it into two parts: first, making sure that your cabling meets the performance requirements for transmission, and secondly, ensuring the network’s compliance with Alien Crosstalk specifications.
Round one of the testing sees each link in the network being tested from both ends, and ensures not only that each component is properly installed, but also that the cabling meets all Category 5e and Category 6 standards of transmission. Newly installed cables are evaluated for 10GBASE-T compliance with a frequency range of 1 through 500MHz. In addition, because any previously existing cables were not tested in a range of this size, all links capable of supporting 10GbE traffic need to be retested.

When each link has been found to have an acceptable level of signal transmission, it is then time to move on to the second part of the evaluation process, which determines whether or not the network’s cabling meets Alien Crosstalk requirements. This phase calls for the installer running the tests to know exactly how the bundled cable in that given network is configured, since each bundle will be measured for combined crosstalk influence, in preparation for a representative link test.

The standard for performing representative AXT evaluations is to test whichever is greater: either five links, or one percent of the installation’s total number of them. The easiest way to go about selecting these test links is to do so while results from the first phase of AXT testing are still organized and available in a computer. The following are a few guidelines along which these “disturbed” or “victim” links are tested.

  • Testing of disturbed links should be conducted from the floor distributor location’s patch panel.

  • As cables get longer, the level of alien crosstalk requirements increases. As a result of this, the installation’s longest links should be chosen as the disturbed links to be tested.

  • The alien crosstalk margin usually improves from 1.5dB to 2.5dB with each corresponding 10 meter link-length reduction, meaning that it isn’t necessary to test shorter links with similar components and configurations once the average AXT margin has reached 5 dB.

The right testing device -- one with good analysis and test result management software -- is also crucial to successfully completing your network’s Alien Crosstalk certification. Fluke Corporation’s DSP Digital CableAnalyzer™ and certification testers, available at, are equipped with LinkWare Cable Test Management software, which allows the user to easily analyze both copper and fiber cabling, as well as review test results. 

Efficient evaluation methods, partnered with versatile testing equipment, can help you accomplish Alien Crosstalk and other network certifications in the shortest amount of time offers the help and resources needed to complete your network evaluation quickly, so that you can be free to move on and tackle your next project!

Fluke DTX CableAnalyzer


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