A reality check on "technical realities"

Magazine was wrong to tell only one side of the Category 7A story.

By Gautier Humbert, Legrand

I highly disagree with the article that supports certain Category 7 arguments. (See "The technical realities of twisted-pair beyond 10G," April 2011, page 11.)

I do understand that the 4-connector, 100-meter channel doesn't make sense in data centers, but 40G and 100G are not only for data centers. They will start there, but extend to the residential and commercial markets later. So creating an Ethernet application for short distance? It's difficult to defend that choice.

As for active equipment manufacturers making equipment for that minute percentage of the market, we've already seen that argument before with 1000Base-TX, which failed.

But there are two points that really bother me.

Shielded. Yes, we all agree that shielded has better performance—in perfect conditions. But don't forget the pair-twist issue. Unshielded twisted-pair (UTP) cables rely only on the pair twist to protect them from electromagnetic interference (EMI). So they have acceptable performance. Shielded/foiled twisted-pair (S/FTP) cables such as Category 7 and Category 7A are fully shielded and offer the best EMI protection, but they have very long twists because they rely only on the shield to block the noise. That means that the added EMI protection they offer is at the cost of a very high sensitivity to noise from the ground. And the shield efficiency is never tested on site. The best of both worlds would be foiled/unshielded twisted-pair (F/UTP), which has a good twist and a shield. So the question: Are shielded cables the future? I would probably agree, but only F/UTP, not S/FTP.

The history of Category 7 and Category 7A. This is nothing against any individual or company, but Category 7 and 7A have a history of receiving optimistic media coverage but failing to live up to that optimism. Other times it has been the subject of reporting that has been simply incorrect. An article published in your own magazine stated, "Class F cabling is the only media to have a 15-year lifecycle." (See "From Category 5e to Class F: De-mystifying cabling specs," April 2007, page 53.) I view Category 7 as having been dead before it even started. So it actually has the lowest lifecycle. And there are no future applications for Category 7.

I am not against any company or individual. But I am against S/FTP cables, Category 7 and Category 7A. I believe Category 7 was invented too soon and has no advantage over Category 6A. As for Category 7A, Category 5e was designed specifically for 1-Gbit/sec. 6A was designed for 10-Gbit/sec. But 7A was designed to achieve a certain frequency. The issue is the applications for Category 7A—there are none. Category 5e UTP can handle a mix of voice and data. Analog video is disappearing because of IPTV. The only chance for Category 7A to survive is for the IEEE to make 40-Gbit/sec Ethernet function on it, even if it is only a 2-connector, 30-meter channel.

The fact that some manufacturers use tools like one-viewpoint white papers to push their solutions is not new. If any company wants to do this, I think they have the right to. But for this magazine to support it, I believe, is a mistake.

Gautier Humbert, RCDD is business development manager for Legrand (www.legrandelectric.com) in East and Central Europe.