cabling

All posts tagged cabling

My readership is limited, so consider a post to be “viral” if I get more than 2 thumbs up at the bottom of a page.  (Incidentally, I’ve only ever gotten one thumbs down, for this post, but I don’t know why.)  My 2021 post For the Love of Wiring got 3 thumbs up (!) but actually did get a lot more hits than usual after Tom Hollingsworth linked to it from his own blog.  How about a little more layer 1?

After my initial foray into stringing Cat 3 cable around in various unwise ways, Category 5 quickly became the standard.  I hated Cat 5 cable.  Cat 3 had a small number of twists per foot (or meter, non-Americans, or metre, Brits!), so upon removing the jacketing of the cable it was quite easy to untwist it before punching it down.  Cat 5 is very twisted.  Not only are the pairs hard to untwist, but they remain kinked after untwisting, and they take a lot of work to smooth out.  (If you correctly terminate Cat 5, you shouldn’t have to untwist and smooth the wires, but I didn’t know that at first.)  I remember once, on my 10 Mbps Ethernet, running a speed test on Cat 3 cable and then being very disappointed when I saw no improvement running the same test over Cat 5.  (Doesn’t quite work that way, and for 10 Mbps, Cat 3 was more than adequate.)

I did a lot of research to learn how to run cable the correct way.  Mainly this means preserving the tight twists.  Cat 5 cable cannot be kinked or bent sharply, and the twists must be maintained up to the point of termination.  Not only did I use this information to run my own cable, but once I took a job at a computer consulting company, I oversaw many cabling projects and needed to inspect the work done by our vendors.  Voice cable did not have the stringent requirements of data, so often phone cabling experts would run the Cat 5 with tight bends and would untwist the wires several inches before punching down.

The consulting company used one such phone installer to do many of their jobs, often as a sub-contractor.  This was in the days before wireless, when every computer connected to the network, even laptops, had to be plugged in.  I remember one client, a small architectural firm in Berkley, where our installer ran a brand new, Cat 5 Ethernet network.  We showed up, installed a hub, Ethernet cards, etc., and got everyone online.

A week or so later we got called back.  Stations were dropping on and off the network.  I fought may way through Bay Area traffic back to the office to figure out what was going on.

With any layer 1 issue, replacing cables is a good first step.  As I unplugged one station from the wall jack, the entire jack and face plate fell off the wall.  Whoops.

Normally when a network jack is installed in an office building with sheetrock (drywall) walls, the installer cuts a fairly large opening in the sheetrock and then installs a “low voltage ring”.  This ring secures to the drywall from behind, and provides a place for the faceplate to screw into.  Then the Cat 5 cable is punched down on a small “keystone” jack, over which a cover is placed, and which then snaps into the faceplate.

Low voltage ring

Our clueless installer had not done this.  Instead he cut a hole in the drywall just small enough for the jack to fit through.  He never installed the low voltage ring, instead screwing the faceplate directly into the drywall.  He also never installed the cover on the contacts on the jack, so the contacts were covered with drywall powder.  Because screws don’t hold well in drywall, when I pulled the cable from the jack, the whole thing fell out.  I also found out that when he had installed the small office patch panel in their supply closet, he put the screws straight into the drywall as well.  Normally you would use a backboard, screw it into a stud, or at least use drywall anchors.  The patch panel fell off the wall too.

Keystone jack with cover

Needless to say, I wasn’t too happy and neither was the customer.  I hate taking the fall for something that’s not my fault, but the customer considered it our mistake.  I made the cabling vendor come out and redo the entire installation.  After that, I told the owner of our firm to never use that vendor again.

A major concern, even with good cabling vendors, was having people in the office around the cables before they were fully installed.  I remember one client where we had a reputable vendor install the cabling before everyone moved in.  They ran one really large bundle of Cat 5 on the floor, because the client was going to install a raised floor afterwards.  Unfortunately, it took them months to get the raised floor in, and the bundle of cable ran right outside of a row of offices.  People stepped on them going in and out of their offices.  One time I remember a guy in cowboy boots standing right on top of the bundle.  I asked him to move.  By the time the floor covered the cables, they had gone from a clean, round bundle, to totally flattened.  Oddly enough, I never had any problems with the wiring in the time I worked there.

When I worked at the San Francisco Chronicle, our cabling vendor was installing some new fiber optic cabling to some data center racks.  The data center also housed our operations team (NOC, more or less.)  There was one lady who worked there who was very nice, rather large, and a tad immature.  The vendor had laid the fiber out on the floor before routing it under the floor tiles.  We looked up and there was the woman, jumping up and down on the fiber and laughing hysterically.  “Is this good for the cables, is this good for the cables?!” she was saying.  When we explained the interior was made out of glass, she looked horrified and stopped, but it was too late.  It cost us a bit, but fortunately for the NOC lady, she was in a union and well protected.

Working on software now, I don’t have to worry about cabling very much anymore.  I touch racks so infrequently I still call SFPs “GBICs”.  I do think it’s good for network engineers to stay informed on layer 1.  As much as you may know about protocols, software defined networking, or automation systems, none of it will work if the wires aren’t right.

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