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Wireless Basics

Performing the Survey

As noted earlier, ther are three types of surveys you can do:

  • Neighboring networks
  • Coverage
  • RF Interference

Neighboring networks

You can perform this survey with either a good wireless client utility or NetStumbler. Since we're looking for neighboring networks, you must shut off your AP or wireless router before starting the survey. If you have noticed wireless problems at certain times of the day or days of the week, be sure to do the scan during those times.

Now open NetStumbler or launch your wireless utility and set it to scan for wireless networks. If you're using a wireless utility, you will probably have to refresh the screen manually;NetStumbler will automatically refresh.

While scanning start in the room where your AP is located, then walk slowly through the area where you desire wireless coverage. Pay special attention to the areas where you most frequently use wireless connections and spend a minute or so there. Refresh the wireless client utility a few times to be sure that it captures any nearby networks.

Even though the antennas built into your notebook or client card are omni-directional, they are still somewhat directional, especially since you're holding the notebook, which blocks some of the signal. So try turning the notebook in different directions while NetStumbler is scanning or trigger a manual scan in each orientation.

Do a screen capture and/or record the SSID, channel number and signal level of any networks you see. Once you've walked the complete area you're done.

When this scan is complete, there are two things that you might want to do right away, depending on the data you've gathered:

  • Change your SSID - If for some reason you haven't followed good security practice and changed your AP's SSID from its default, you should do it now. Check the list of neighboring networks you've found and make sure your new SSID is different.

  • Change your Channel - If you've found neighboring networks that are using the same channel as your AP, change it to a different channel, sticking with the choices of Channels 1, 6 or 11. Use whichever channel isn't already in use. If all channels are in use, set your AP's channel to the same one as the weakest network that you found, i.e. the one closer to - 100 dBm. This will give you the best shot at trouble-free operation.

Wireless Coverage

In a wireless coverage scan, you're looking to assess the signal level of your AP, so first make sure that it is on. Start with your notebook in the same room as your AP, fire up Netstumbler and expand either the Channel or SSID tree in the left-hand pane until you get the signal vs. time plot.

Do the same walk as before, making sure to visit the areas where you have particular trouble either getting or keeping a wireless connection. At each location, record the signal level of your AP, making special note of locations where the level disappears, indicated by the green dot in the left-hand pane turning grey and gaps in the plot (Figure 6).

NetStumbler Example Scan 1
Click to enlarge image

Figure 6: NetStumbler Example Scan 1
TipTip:As good as NetStumbler is, sometimes it doesn't quite show what's really going on. For example, if you get a constant signal level no matter how far you move your notebook away from you AP, then you'll need to try another card. You don't have a super AP, but just an incompatibility between NetStumbler and the card you're using.

In other cases, NetStumbler might not show a disconnect from your AP. Figure 7 shows an adapter that didn't disconnect, but instead showed a constant low signal level when it actually had lost connection.

NetStumbler Example Scan 2
Click to enlarge image

Figure 7: NetStumbler Example Scan 2

If you're using a wireless client utilty, record the signal, signal quality or whatever signal value the utility provides and where your network disappears from the wireless client utility list of networks.

If your scan found that you lost connection with your AP in places where you need to be connected, the only simple thing you can do at this point is to try to move your AP. Sometimes even just moving if from one side of the room to another, or placing it as high as possible in the room (on top of a bookcase, for example) might make the difference. Solving wireless coverage problems is a pretty broad subject and will be the subject of a future How To.

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