Warum sind Kabel der Kategorie 7 (und die Kategorie 8) nicht so erfolgreich?

 

Category 5e, 6 and 6A are Ethernet cable types that the industry knows a lot about; they're used frequently. But what about Category 7 and 7A-or Category 8? We don't hear nearly as much about these cables. On paper, they may seem like a good and logical next step after Category 6A to support emerging technology. But is that really true?

 

What is Category 7 Cable?

In terms of bandwidth, Category 7 has a transmission performance of 600 MHz; Category 7A operates at 1,000 MHz. Both are fully shielded S/FTP cables.

 

In comparison, Category 6A cables operate at 500 MHz. Although that’s a lower speed, it easily supports today’s 10GBASE-T applications (with Ethernet speeds of 10 Gb/s, a bandwidth of only 400 MHz is needed for 10GBASE-T). The 500 MHz limit of Category 6A cables includes a 20% guard band required by equipment manufacturers.

 

In parts of Europe where shielded cabling is the standard to support EMC regulations, Category 7 and 7A cabling have been specified with the idea that this would be needed for future applications. But here in North America (where unshielded cabling reigns), Category 7 and 7A cables simply aren't specified. Why? Because there are no technology applications that require them.

 

Also, Category 7 and 7A cables aren't TIA-recognized standards. (To properly compare TIA categories, we should actually compare to ISO Class F/FA cabling systems.) A true Category 7 infrastructure using Category 7 components supports an ISO Class F system; Category 7A infrastructure using Category 7A components supports an ISO Class FA system.

 

In LAN applications, ISO Class F/FA doesn't support any existing or emerging technology applications. The same holds true for data center applications. There's no demand for Category 7 or 7A cables in North America because there's no need for them.

 

When Should You Use Category 7 or 7A Cable?

Why should you ever choose a Category 7 or 7A cabling system? The short answer: You shouldn't. If you do, then you're making the decision to pay more for these cables when a lower-cost Category 6A system would perform just as well.

 

In addition, in order to connect Category 7 cable to your network, you’ll likely use RJ45 Category 6A connectors. While Category 7 connectors do exist (non-split-pair connectors, such as ARJ45, for example), today’s equipment (routers, switches, servers, etc.) isn’t designed to support this type of connectivity.

 

When you use Category 6A connectors, you turn a Category 7 or 7A system into a Category 6A system—and you have to measure and test it as such. When lower-Category components connect to higher-Category components, the system drops to the performance level of the lowest Category used within the system. For example: If you deploy a Category 7 cable using Category 6A components, then you have a Category 6A system—not a Category 7 system.

 

If this seems confusing, a garden hose is a good comparison to think about. You may have a one-inch hose in your backyard, but what if the spigot has a half-inch faucet? You can only connect to it with a half-inch coupling. That small opening reduces the amount of water that can move through the hose, even though the hose itself could handle more. Instead of investing in a one-inch hose, you could've used a half-inch hose and saved some money. In both cases, the amount of water moving through the hose will be the same.

 

Where Does Category 8 Fit In?

As conversations moved from 10GBASE-T to 25GBASE-T and 40GBASE-T technologies, existing Category 7 and 7A components (thought to be futureproof solutions!) did not have sufficient bandwidth to fully support these higher speeds.

 

During the development of 25GBASE-T and 40GBASE-T, equipment suppliers demanded that connectivity be backward compatible to all existing equipment. Thus, IEEE defined the link segment limits to use RJ45 connectivity. TIA Category 8 and ISO/IEC Class I (using Category 8.1 components) utilize backward-compatible RJ45 connectivity and ISO/IEC Class II (using Category 8.2 components) utilize unique connectivity not used in lower Categories or classes. All are specified to 2,000 MHz at a reach of 30 m for 25GBASE-T and 40GBASE-T. But this reach limitation, combined with a large OD, makes Category 8 cable difficult to use-and an upgrade path from 100 m Category 6A to 30 m Category 8 doesn't exist.

 

During the time Category 8 cable was introduced, fiber optic transceivers were also coming down in price. Instead of running 25GBASE-T or 40GBASE-T over copper, many people began to support these speeds with fiber instead. Using fiber also ensures that your cabling infrastructure is set up for whatever technologies the future may bring.

 

Making Your Decision

Wondering about Category 6A, 7, 7A or 8 cable for your next project? Belden can answer your questions and steer you in the right direction based on the application and your goals.

 

As your trusted advisor, we want to make sure you get the most from your cabling investment—without overspending on a system that will never provide what you need or expect.