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OS X Lion Wi-Fi Diagnostics

How to Use Lion's Built-in Wireless Diagnostic System

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OS X Lion Wi-Fi Diagnostics

After I fiddled with the wireless router's location, the noise level fell and the signal level increased.

Screen shot courtesy of Coyote Moon, Inc.

OS X Lion includes a built-in Wi-Fi Diagnostics application that you can use to troubleshoot your wireless network connection. You can also use it to tweak your Wi-Fi connection for best performance.

The Wi-Fi Diagnostics app has four main functions:

Monitor Performance - Provides a near real-time graph of signal strength and signal noise. Also generates a log of signal performance over time.

Record Events - Can log specific events, such as users connecting to or disconnecting from the Wi-Fi network.

Capture Raw Frames - Allows you to capture data sent over the wireless network, data sent or received by your computer over the wireless network, and data from any nearby network to which you have access rights.

Turn on Debug Logs - Allows you to capture debug-level events occurring on your wireless network.

You can use any one of the four functions individually. You cannot combine multiple functions, such as monitoring signal strength while you capture raw frames.

The most useful of the four functions for most Mac users is the one that monitors signal strength and noise. With this near real-time graph, you can discover what is causing your wireless connection to drop from time to time. You may find that whenever your wireless phone rings, the noise floor jumps up to squash the signal received, or maybe it happens when you're microwaving pizza for lunch.

You may also see that the signal strength is marginal, and that moving your wireless router may improve the Wi-Fi connection's performance.

The other useful tool is for recording events. If you have been wondering if anyone is attempting to connect to your wireless network (and perhaps succeeding), the Record Events function can provide the answer. Whenever someone attempts to connect, or does connect, to your network, the connection will be logged, along with the time and date. If you didn't make a connection at the time, you may want to find out who did.

If you need a bit more detail than Record Events can provide, you can try the Turn on Debug Logs option, which will log details of every wireless connection made or dropped.

And for those who really want to get down to the nitty-gritty of debugging a network, Capture Raw Frames will do just that; it captures all traffic on the wireless network for later analysis.

Using the OS X Lion Wi-Fi Diagnostics

  1. Launch the Wi-Fi Diagnostics application, located at /System/Library/CoreServices/.

  2. The Wi-Fi Diagnostics application will open and present you with the option to select one of the four available functions:
    • Monitor Performance

    • Record Events

    • Capture Raw Frames

    • Turn on Debug Logs
  3. You can make your selection by clicking the radio button next to the desired function. For this example, we're going to select the Monitor Performance function. Click Continue

  4. The Wi-Fi Diagnostics application will display a near real-time graph showing you the signal and noise level over time. If you're trying to discover what is causing noise problems, you can try turning off or on various appliances, services, or other noise-generating items you may have in your home and office, and see how it affects the noise level.

  5. If you're trying to gain a better signal, move either the antenna or the entire wireless router or adapter to another location to see how it affects the signal level. I discovered that just rotating one of the antennas on my wireless router improved the signal level.

  6. The signal and noise level display shows just the last two minutes of your wireless connection's performance, however, all of the data is maintained in a performance log.
  7. Accessing the Monitor Performance Log

  8. With the Monitor Performance graph still displayed, click the Continue button.

  9. You can choose to save the log to the Finder or send it as an email. I've not been able to successfully use the Send as Email option, so I suggest selecting the Show in Finder option. Click the Report button.

  10. The report is saved to your desktop in a compressed format.

  11. Double-click the diagnostic file to decompress the report.

The report files are saved in various formats, depending on which function you were using. Most reports are saved in Apple's plist format, which can be read by most XML editors. The other format you will see is the pcap format, which is used by most network packet capture applications, such as WireShark. For the most part, the reports that the Wi-Fi Diagnostics app creates aren't that usable for casual users just trying to get their wireless network up and running. Instead, you should use the Wi-Fi Diagnostics app's built-in viewers for each function.

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