Smart Building

What You Need to Know About Alien Crosstalk Today

Ron Tellas

The industry has been predicting the growth of 10GBASE-T for years, and it’s finally happening. More networks are planning 10G migrations. Why? Due to demand from more advanced devices, users and applications.

But new concerns come into play with this Ethernet standard. Alien crosstalk – the interference caused by wire pairs in one cable inducing noise into other wire pairs in adjacent cables – is the transmission parameter that most significantly impacts 10GBASE-T performance.


What is Alien Crosstalk?

Alien crosstalk is a combination of alien near-end crosstalk (NEXT) and alien far-end crosstalk (FEXT); the noise source originates from a common mode signal that is converted onto the differential mode signal through some type unbalance on cable and components.


Why is Alien Crosstalk Bad for Today’s Applications?

In high-speed, high-bandwidth applications – used today to accommodate more users and more devices – alien crosstalk can cause many problems. In a cable bundle, it’s possible that cable pairs in one cable pick up interference from pairs of another cable. The digital signal processors (DSPs) used in 10GBASE-T architectures can’t remove unpredictable exterior noise. Noise sensitivity increases at higher frequencies, such as 500 MHz, which is the highest frequency of Category 6A cabling.

This interference isn’t just a nuisance; it has the potential to shut your entire network down – which leads to unplanned downtime, financial losses, a productivity nosedive and unhappy users.


What Causes Alien Crosstalk?

Alien crosstalk originates from a common mode signal that is converted onto the differential mode signal through some type of unbalance on the cable and components. Category 6A cabling and components are designed and tested to reduce alien crosstalk to a level low enough that it does not interfere with the differential mode signal. 


Make sure all components are Category 6A>. This is especially important to note for patch cords. When high-quality, Category 6 cable is tested, it may pass Category 6A patch cord requirements because only near-end crosstalk and return loss are measured. When these patch cords are bundled and placed in a Category 6A channel, however, the channel fails alien crosstalk requirements. Why? Because Category 6 cable isn’t designed to handle high data-speed requirements.


Don’t over-tighten cable ties. Cable ties that increase tension can force cables together and impact alien crosstalk. When using cabling ties to dress the cabling, make sure the ties are free to rotate after tightening.


What Do Standards Say About Alien Crosstalk?

Alien crosstalk reduces cabling’s operational bandwidth due to increased channel noise levels; as a result, ANSI/TIA standards state that Category 6A cabling best meets the demands of 10G. (According to current standards, Class E and Category 6 cabling aren’t recommended for new 10GBASE-T installations over 37m.)


Here are a few reasons why Category 6A is the best choice:

  • Achieving 10GBASE-T over copper requires 500 MHz bandwidth and full duplex transmission, which Category 6A provides
  • It must follow stringent ISO/IEC and ANSI/TIA transmission-parameter regulations
  • It uses specially designed jackets and cross-webs that physically separate internal twisted pairs from external twisted pairs, ensuring low alien crosstalk
  • It provides a guaranteed alien crosstalk margin above minimum TIA-568-C.2 requirements
  • Category 6A specifications allow compliant cabling for 10GBASE-T transmission

Belden’s Category 6A cabling solutions provide a simple design without compromising performance or quality, ensuring robust performance and reliable networks. Learn more about our 10GXS cables, which feature a smaller diameter, a rounder jacket, a smaller bend radius, fewer twists and easy-to-remove barrier tape.