Wednesday, 6 February 2008

Aliens cause trouble in cabling

The menace has always been there but, until now, it's not been causing a problem. It's alien crosstalk and it's the effect of signals in one cable causing interference in an adjacent cable. Actually, a cable gets a sum of alien crosstalk from all of its adjacent cables.

The good news is that alien crosstalk has negligable effect in a network until you start to use 10Gigabit Ethenet (10GBase-T). The high frequencies and sensitive encoding make it susceptable but there are things we can do to mitigate the effects. The best solution is to use a Cat6a / Class Ea cabling system. Although this is not yet fully ratified, there are systems on the market that conform to the draft standard. An alternative is to use Cat6 up to distances of 35 metres (some say 55 metres) but make sure it's installed with loose looms to mitigate against alien crosstalk.

Testing for alien crosstalk in the field is time consuming and it's virtually impossible to do with 100% certainty; that would mean putting signal on to every cable and then testing each cable as a victim cable.

Luckily, the better companies in the data cabling industry are able to provide clients with cabling systems that will work at 10G so those aliens needn't bother you.

Alan Bullen
Lynx Networks plc

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