Saturday, 25 February 2017

CWAP Study Notes Files

A while back I published my CWAP study notes on another blogging platform which I've since abandoned. I've had another request to re-publish them, so here they are for your reading pleasure.

Note that these apply to an older version of the CWAP exam, but still have some great information summarized in there.

Here are the files I put together for each chapter. I fizzled out note-taking wise at chapter 10 (802.11 HT) , hence its omission from this list (sorry!).

CWAP study note files:

Wednesday, 21 September 2016

Getting Data Out of the Windows ‘netsh wlan show interfaces’ Command

I recently read a very nice article by Matt Frederick about using a Windows command prompt utility to gain information about what your Windows wireless adapter is up to while connected to a Wi-Fi network (

In  Matt’s article, he described how he wrapped the ‘netsh’ command into a nice little batch file to run the command regularly, allowing information to be presented in a more dynamic fashion.

I was so impressed with the information provided by the utility, that I decided I’d  try to get the information it provides into a more usable format. In short, I hacked together a Windows Powersell script that runs the ‘netsh’ CLI utility regularly and parses the output data into a CSV format.

By piping the output into a file, you can get a nice CSV file that can be opened in Excel to look at the raw data over a period of time. It’s great for looking at the adapter signal level and BSSID information - it’s easy to spot when your client roams and the approximate signal level at which this takes place.

Fig 1 - You can get output like this...unless you've got good eye-sight, it's better in a CSV :)

A few caveats:

  • I’m not  a coder - this is my first Powershell script
  • This isn’t a robust piece of supported code - it will break easily over time when the output of the ‘netsh’ command changes (refer to the previous bullet)
  • The ‘netsh’ utility natively provides RSSI data as  percentage figure. I’ve converted it to dBm in the script, but the highest dBm figure you’ll ever see is 50dBm ( which is 100% in the ‘netsh’ utility output)...don’t shoot the messenger on that one.
  • This was a bit of fun to do - have fun with it yourself, but don’t get too angry if it doesn't work for you :)
  • Open the script file with Notepad and read ALL of the notes at the top of the file that explain how to use the script.

There are a few challenges getting the script to run without lots of warnings in Powershell - open the script file and read the notes at the top of the file.

By default, the script runs every second, which is nice to roam around and capture regular data. Change the variable ‘$SleepInterval’ at the beginning of the code if you’d like to extend it to a more infrequent interval (2 = 2 secs, 3 = 3 secs etc…)

Again, have fun with it...oh yes, you can find the script here:


Friday, 26 February 2016

802.3af Is Dead (For Surveys)

I’ve recently been involved with a project that has brought me into contact with a number of wireless engineers who are performing WLAN survey work using the traditional “AP on a stick” (APOAS) survey method. Yes, there are plenty of people out there who still prefer this method, or have customers who demand it.

One thing that has become apparent is that a number of people are still using power sources (generally a battery pack) for their survey AP that still only supports the 802.3af POE (power over Ethernet) standard.

The time has come for those using these legacy power supplies to make an investment and  upgrade their AP power packs to support the higher power provided by the 802.3at standard. The next generation of wireless access points simply won’t allow the continued use of 802.3af power packs, due to the enhanced power requirements of modern APs.


Until relatively recently, many Enterprise grade wireless access points have been able to work with the power budget imposed by the 802.3af POE standard. This means that they are able to work with a power draw of 15.4W or less.

This was sufficient for many APs until the advent of the next generation 802.11ac (“Gigabit Wireless”), back in late 2013. Even after the emergence of this first "wave" of 802.11ac APs, some models could just about fit within the 15.4W power budget of 802.3af POE, or at least run with a reduced feature set that would allow it to be used for a basic RF passive survey.

Example of the types of power pack previously used included the Terrawave battery pack and the Pointsource POE Injector. Whilst these were a reasonable choice as an 802.3af power source, they simply can’t provide the power requirements of newer wireless APs.

802.11ac Wave 2

With the emergence of the “latest and greatest” 802.11ac “Wave 2” access points, the lowly 802.3af POE supply can no longer be used for APOAS surveying.

The additional power requirements of “Wave 2” APs means that a 802.3at power pack must now be available for survey work. This new generation of APs have additional features such as MU-MIMO (multi-user MIMO) and additional radio chains that mean that the legacy 802.3af (15W) power budget simply isn’t enough.

(Note: You may also see 802.3at referred to as "POE+" in some documents)

So, the time has come to put our old, trusty 802.3af power packs out to pasture and ensure we have a power supply that can support 802.3at, and is able to meet the higher power budgets of this next generation of APs.

Power packs that support the 802.3at standard will be able to supply a power draw in excess of 25W, providing a significant increase from the previous 15.4W that we could achieve with 802.3af.

Suggested Power Packs
A quick “Google” around the Internet doesn’t yield any useful results when trying to find a 802.3at POE battery pack - well none that I have found so far with my great sausage fingers…. (update: see end of this article for some suggestions)

A great solution is a home-brew solution that is the subject of a great blog article by Scott Stapleton. It details how to create a 802.3at power pack using a lithium battery pack and POE DC-DC converter. I suggest you get along to his article to find out how to build your own 802.3at power supply. It’s very straightforward to build and turns out to be smaller, lighter and has a higher capacity than the previous lead-acid battery based solutions.

If anyone has any other suggestions for any “off the shelf” 802.3at POE power pack solutions suitable for surveying, please include them in the comments section of this article.

My Power Pack
Here are some pictures of my current AP power pack, based on Scott’s great article, so you can get an idea of what a build-your-own solution might look like. Admittedly, mine looks a little “home made”, but it does the job and lasts many hours on-site - you can get a full day out of a pack like this, depending on the battery you buy, AP power settings etc.

Fig 1 - Yes, I have to label everything

Fig 2 - A side-on view so that you can appreciate the full beauty of this work of art

(Note: the cut-off RJ45 lug is to stop me plugging the AP into the non-POE port, which causes me to swear under my breath)

I’m sure there are plenty of you out there that could come up with something far more aesthetically pleasing (and that looks less like a bomb…)


Get along to Scott’s blog article for full details of how to build your own 802.3at survey power pack.

My components:
  • Battery: Aukey 28000mAH External Battery Pack (UK Amazon link)
  • Converter: Tycon Power 24v-48V DC To DC Gigabit POE (UK Supplier Link)
  • Lots of gaffer tape


Here are some off the shelf survey batteries you might also like to take a look at: