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: Chapter 1 - 802.11 Overview Chapter 2 - Physical Layer Format Chapter 3 - 802.11 MAC Sub-layer Frame Format Chapter 4 - 802.11 Management Frames Chapter 5 - 802.1 Control Frames Chapter 6 - Data Frames Chapter 7 - 802.11 Medium Contention Chapter 8 - Power Management Chapter 9  802.11 Security

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

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. Background Until relatively recently, many Enterprise grade wireless access points have been able to work with the

How Fast Is My Wi-Fi Client?

In the Wi-Fi For Beginners podcast, I've spent a lot of time talking about WLAN clients . Understanding their characteristics, capabilities and behavior is crucial when designing and deploying a wireless LAN. Without understanding the clients on your network, you will not be able to anticipate their demands on your WLAN infrastructure and the level of performance that you will be able to realistically be able to provide to end users . The discussion about WLAN clients is fairly extensive and spans a number of episodes as this is such an important topic. In the podcast I highlight the importance of understanding the capabilities of the clients that connect to a WLAN. Just because you buy yourself a nice new shiny smartphone that (you hope) supports 802.11ac, doesn't mean you are going to get 1.3Gbps of throughput when you hook it up to your Wi-Fi network. Unless you understand its capabilities in terms of 802.11 amendment support, number of streams available etc., then you

Measuring Obstruction Losses For WLAN Predictive Modelling

I recently attended the Ekahau Certified Survey Engineer (ECSE) training course, presented by Keith Parsons. In addition to learning about using Ekahau Site Survey  (ESS), Keith also shared some valuable insights in to best practice wireless LAN design and surveying techniques. One of these insights was a best practice approach to measuring loss through obstructions and attenuation areas, such as doors, walls and warehouse racking, when gathering data for a WLAN predictive model.  In this article, I’ll share the details of that approach and some mistakes you might be making in your own measuring approach. Please visit the Ekahau blog site to see my guest posting for the full details on this topic.

Do Cisco AP LEDs Ever Flash Once Disabled?

A quick post about an interesting question on Twitter about disabling indicator LEDs on Cisco APs: There are often times when a customer would like the LEDs disabled on Cisco APs. Examples include education and healthcare environments when the LEDs may be perceived as being annoying or distracting if left illuminated. The LED may be disabled by two methods: CLI :  config ap led-state disable <ap name> WLC GUI (AireOs): Wireless > All APs > [Select AP] > Advanced > Led State (see screen-shot below) Fig. Disable AP LED from WLC GUI However, once the AP indicator LED has been disabled, does it remain disabled at all times? I setup this up in my lab and did a quick test with an AP3600 running code on the WLC. I tested 4 scenarios to see if the AP lamps remains extinguished, or would become illuminated. Here are the results: Normal operation: LED off AP lost contact with the WLC: LED off AP power cycled: Flashing LED during boot seq

Wi-Fi EIRP Calculator

As a Wi-Fi engineer, there are a number of occasions when it is useful to understand the EIRP ("Effective Isotropically Radiated Power) of a system. (I'll leave to you to read this Wikipedia link for an EIRP explanation). This is often a requirement when using external antennas on an access point or perhaps using tools (e.g. survey software) which require you to account for the various gains and losses in a system. Calculating EIRP is crucial to understand the power level that will actually end up radiating out of your antenna. This is often for reasons of regulatory compliance, coverage considerations or perhaps matching the power of client devices. As this is something I seem to have to do on a fairly regular basis, I thought I'd knock up an EIRP calculator to add to my website . To calculate the EIRP of a system, enter the AP transmit power, the loss of any cable and connectors  and the gain of the antenna. Note that if you are using an AP with an internal anten