Making the connection

Cable and connectivity must work together in order to be effective.
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Information technology depends on reliable connections from point to point. Of course, at the ends you can put wireless devices, but those are really just the last few feet. Wireless backbones are a lot harder. As our demand for bandwidth goes up, it becomes increasingly harder for reliable wire and wireless connections.


The vast majority of data cabling in the Americas is unshielded twisted pairs (UTP). With one exception in this article, we will concentrate on UTP.

As most installers know, cable and connectivity must work together to be effective. The problem is that connectorization, for a lot of reasons, is not easy. This is why the cable-connector interface is where most network systems fail. Table 1 lists the reasons why networks fail at the connector.

Reasons for failure

The real problem for broadcasters is that their architecture for broadcast facilities is often different from classic network wiring. To explain that, we need to look back in history. Back around 1990, we were living in a Cat 3 world. Cat 3 was the first four-pair data cable. It had a bandwidth of 16MHz. It was easy to put in. (Heck, it's now the telephone cable standard.)

At that time, some industry players did a few surveys to find out why networks failed. The No. 1 answer was owner-installed plugs. Yes, those RJ-45 male plugs were put on poorly or with the wrong wiring order, and the network just didn't work. As a result, many manufacturers provided RJ-45 jacks (female) and sold patch cords. They could then control the male plugs, since they made the patch cord themselves.

This continued through Cat 4 (now dead and gone), Cat 5 (ancient) and Cat 5e (the common low-end). However, finding plugs for Cat 6 (the good stuff) and Cat 6a (augmented Cat 6 and top-of-the-line) is difficult. There are a few advertised, but the failure rate is alarming — up to 70 percent for some nice-looking connectors.

With the jack-and-patchcord style of networking, you're home free. That usually means a plastic wallplate with square holes (called keystone). You punch down the wires on the jack, which is quite easy, so it's difficult to get the wiring order wrong. Click the jack into the wallplate, and put the plate into the box in the wall. Then buy a patchcord of the correct length, and plug in the end-user.

It works great in an office. For broadcasters, however, this often doesn't work. Broadcasters want to go from Point A to Point B, like with audio and video cable. What are you going to do with the jack? Hang it in mid-air? No, what you want is a plug on each end of the cable.

And there lies the problem. You can buy the fanciest, bonded-pair, Cat 6, but if you put a 5e plug on it, you have a cable with 5e performance. You might as well have put in 5e cable and saved some money!

Prevention

Here's what I suggest. First, take the installation team to some data networking/installation classes. Learn how professional network installers put that stuff in. Second, insist that part of the course be the wiring of RJ-45 male plugs.

Third, buy one of the really good (and expensive) handheld testers, and take a class on how to use it. Nothing reveals how good an installation is like real live testing.

Fourth, write or e-mail all those plug and jack manufacturers, and ask for the data on the male plugs they will sell to you (many of the plugs are not for sale). Look especially at the Cat 6 data, and maybe even get some samples. Send the manufacturers a piece of the cable you want to use and have them put a connector on each end. Then you can test that cable in your new tester. If they can do it, theoretically, you can do it.

Of course, after choosing, you'll have to spend a few bucks on RJ-45 crimp tools as well.

Unfortunately, my scenario falls apart when we get to Cat 6a. This is 10GBASE-T, or 10Gb/s networking cable. The standard 10Gig cable has a bandwidth of 500MHz per pair. To attain as much futureproofing as possible, this is the way to go.

At those frequencies, the emission of signals is a huge problem, and the slightest error can crash a system. This is why it's so hard to put in. Figure 1 shows a 10Gig jack. Most jacks line the wires up in a row so you can punch them down. This is fine for Cat 5e or 6, but way too much crosstalk for Cat 6a.

With the 10Gig jack, the pairs are at right angles to each other. (Of course, you remember being told that if you cross a power cord with an audio snake, do it at right angles.) That little red thing helps keep the pairs in the right order.

The front of this jack is equally weird. (See Figure 2 on page 82.) It's still a RJ-45, but those are not eight little wires anymore. That's a flexible printed circuit in there, where the spaces between the traces have been cut out. This gives impedance stability previously unknown.

Options

So what can you do? To go as far in the future as possible, go Cat 6a. However, this means figuring out how to make the plug-and-patchcord system work for your facility.

The simplest option is Cat 5e, where everything is easy to put in, including plugs. It allows the flexibility to do whatever you want, including point-to-point wiring.

Or you can put in Cat 6, and strong-arm the connector guys to provide plugs that will actually work. Cat 6, by the way, will carry a 10Gig signal for 55m, until the cables interfere with each other and fail because of alien crosstalk. That's why Cat 6a cable has something in it that pushes the other cables away. (See Figure 3.)

Some manufacturers are making 10Gig with individually shielded pairs. Those cables would be the easy way to 10Gig, but they are much harder to install, with the shields and drain wires. Also, at 500MHz, a low impedance to ground is needed to effectively get rid of noise. But a low impedance is hard to get even at moderately high frequencies.

Ground loop problems (unknown in the UTP world) can also occur. To fix this, cut one ground. The result looks like an open circuit at every quarter wavelength, shown in Figure 4.

There is one other option. You can always put in high-performance UTP cable and use it for low-performance applications. You could easily put a Cat 5e plug (or jack) on 10Gig. It then would be a 5e cable, until you come back and put a 6a plug on it in the future. This, of course, assumes that there will be a 6a plug available for field installation in the future!

Besides all these options, the one thing that I strongly encourage is to get educated. Whether you like it or not, you are now a data dude. Learn all that you can.

Steve Lampen is a multimedia technology manager for Belden.

Table 1. Network systems fail at the connector for many reasons. Reason Effect Comment Wrong wiring order No connections EIA/TIA 568 A or B Wrong plug Reduced bandwidth Using Cat 5e connector on Cat 6 cable Poor wiring Crosstalk, reflection Take a wiring class