Wireles Networking is a practical guide to planning and building low-cost telecommunications infrastructure. See the editorial for more information....

Proper Troubleshooting Technique

No troubleshooting methodology can completely cover all problems you will encounter when working with wireless networks. But often, problems come down to one of a few common mistakes. Here are a few simple points to keep in mind that can get your troubleshooting effort working in the right direction.

  • Don't panic. If you are troubleshooting a system, that means that it was working at one time, probably very recently. Before jumping in and making changes, survey the scene and assess exactly what is broken. If you have historical logs or statistics to work from, all the better. Be sure to collect information first, so you can make an informed decision before making changes.
  • Is it plugged in? This step is often overlooked until many other avenues are explored. Plugs can be accidentally (or intentionally) unplugged very easily. Is the lead connected to a good power source? Is the other end connected to your device? Is the power light on? It may sound silly, but you will feel even sillier if you spend a lot of time checking out an antenna feed line only to realize that the AP was unplugged the entire time. Trust me, it happens more often than most of us would care to admit.
  • What was the last thing changed? If you are the only person with access to the system, what is the last change you made? If others have access to it, what is the last change they made and when? When was the last time the system worked? Often, system changes have unintended consequences that may not be immediately noticed. Roll back that change and see what effect it has on the problem.
  • Make a backup. This applies before you notice problems, as well as after. If you make a complicated software change to a system, having a backup means that you can quickly restore it to the previous settings and start again. When troubleshooting very complex problems, having a configuration that “sort-of” works can be much better than having a mess that doesn't work at all (and that you can't easily restore from memory).
  • The known good. This idea applies to hardware, as well as software. A known good is any component that you can replace in a complex system to verify that its counterpart is in good, working condition. For example, you may carry a tested Ethernet cable in a tool kit. If you suspect problems with a cable in the field, you can easily swap out the suspect cable with the known good and see if things improve. This is much faster and less error-prone than re-crimping a cable, and immediately tells you if the change fixes the problem. Likewise, you may also pack a backup battery, antenna cable, or a CD-ROM with a known good configuration for the system. When fixing complicated problems, saving your work at a given point lets you return to it as a known good, even if the problem is not yet completely solved.
  • Change one variable at a time. When under pressure to get a failed system back online, it is tempting to jump ahead and change many likely variables at once. If you do, and your changes seem to fix the problem, then you will not understand exactly what led to the problem in the first place. Worse, your changes may fix the original problem, but lead to more unintended consequences that break other parts of the system. By changing your variables one at a time, you can precisely understand what went wrong in the first place, and be able to see the direct effects of the changes you make.
  • Do no harm. If you don't fully understand how a system works, don'tbe afraid to call in an expert. If you are not sure if a particular change will damage another part of the system, then either find someone with more experience or devise a way to test your change without doing damage. Putting a penny in place of a fuse may solve the immediate problem, but it may also burn down the building.

It is unlikely that the people who design your network will be on call twenty-four hours per day to fix problems when they arise. Your troubleshooting team will need to have good troubleshooting skills, but may not be competent enough to configure a router from scratch or crimp a piece of LMR-400. It is often much more efficient to have a number of backup components on-hand, and train your team to be able to swap out the entire broken part. This could mean having an access point or router pre-configured and sitting in a locked cabinet, plainly labeled and stored with backup cables and power supplies. Your team can swap out the failed component, and either send the broken part to an expert for repair, or arrange to have another backup sent in. Assuming that the backups are kept secure and are replaced when used, this can save a lot of time for everyone.

Last Update: 2007-01-15