In-Depth

Wireless Meets Mother Nature

It’s important to remember that the answer’s not always in a book or taught in a class, as we found out when investigating a disrupted wireless link.

• By Justin L. Melot
• 10/01/2002

I was responsible for all offsite facilities, which wasn’t a bad gig: It got me out of the office, away from the boss, and trips were usually short and sweet. One morning a call came in that an offsite location had entirely lost connectivity. This particular site, as well as several others, had a wireless WAN link that stretched a couple of miles across town. The site’s two-story building was square, perfect for mounting an antenna on top.

By the time I arrived, the whole system was up and running normally. The users told me they didn’t know what happened; they kept trying to log in, and the network finally let them.

It appeared to be a fluke; I’ve seen them before. But then it happened again, and the problem repeated itself. I made five or six trips back and forth that day, and practically every day for several weeks, each time for the same connectivity problem. It was hard to tell if I ever fixed it, because some days I wouldn’t hear from them and the next day I would. Finally, I started asking colleagues to come and prove I wasn’t crazy.

We checked everything inside and out, but found nothing. Finally, we plugged a laptop into the switch at the offsite location, ran a continuous packet count using PING with TCP/IP and let it run for several minutes. It would send and receive packets at 100 percent, then all of a sudden it would drop everything. If we waited, though, it would jump back up and work like a champ.

We spent several days lining up our antenna with the marks we’d tested and made to line up across town at the hospital. One frustrating afternoon, as the network administrator and I stood on the roof of the building scratching our heads over this puzzle, he decided to lay his face down on the antenna and look down it like the barrel of a gun.

Between the branch office and the hospital is a beautiful golf course, which the network admin and I had played several times together. One thing that makes this course so nice (and evil in some cases) is that it has several large trees. As we looked down the barrel of the antenna, we noticed a tree growing in the path of the hospital and the site’s antenna a mile or two away from us.

Further investigation revealed that the tree had grown just inside the wireless transmission path from the time the antenna had been placed; once its leaves blossomed, the tree started blocking our transmissions. The kicker is that it wasn’t always in the way; a strong wind—a nearly everyday occurrence in Oklahoma’s spring and summer—would push the tree in the way and block the transmission.

We discussed the proper time that evening to jump the fence with a chainsaw and cut that tree down. Eventually, though, we came to our senses and decided that we should just raise the antenna another ten feet. How long that will work I don’t know, but I do know that’ll be the first thing checked the next time there is a rash of disconnects.

It’s important to remember that the answer’s not always in a book or taught in a class. So often I meet “certified technicians” that haven’t learned to think outside the box. That’s a valuable lesson.