Tuesday, July 17, 2007

cat6a, cat7 and all that 10gig stuff!

I spent a day at Tyco in Stanmore doing some training on the newest types of ten gigabit network cables. Since there is no ratified standard for ethernet at this data rate (even though both Intel and Cisco have products) everyone is referring to it with different terminology. The Germans refer to the cable as cat7, the Americans as cat6a (the 'a' is augmented) and Tyco (who seem to have the biggest portfolio so far) as XG-10gig cable.
We spent the morning going over the physics of it all - the new cable is a 600Mhz channel and by QAM64 and OFDM (which I blogged about recently) signal processing techniques they can get ten gigabits per sec down one hundred metres of cable. If you use earlier cat5e or cat6 cable you are pretty much limited to sub-30m lengths.
The differences in cable and termination are sufficiently marked with respect to vanilla cat6 as to require different tools and techniques and everything is specified (even down to the sub-50N of force you can apply when pulling it into ducts). They seem to have woken up to the fact that relying on common-mode rejection as the only means of noise reduction is flawed and consequently this new cable is double-screened - the pairs are individually shielded and there is an overall screen. This is why the cable is also referred to as PIMF (pairs in metal foil).
Reasons for differences;

  • Near-end cross talk is dramatically reduced by virtue of the new ends and termination tool. When properly terminated the twisted pair and shield is maintained to within a couple of millimeters of the pin on the connector. You could never achieve this with traditional punch-down methods.

  • Alien cross-talk is minimised by the over-shield - cat5e and cat6 never really enjoyed this advantage.

  • Inter-pair cross-talk is minimised by the foil shield around each of the pairs.
There is no RJ45 plug that can be crimped on - you can only buy pre-made patch cords. Panel to panel wiring is the only termination type permitted on site.
This has to be the future of data-centre wiring - we're currently doing a job that involved 600-odd circuits like this (and it's in a visual-effects company), however - I never imagined I'd have gigabit at home and it can only be a couple of years before ten-gig ethernet is ubiquitous.

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