CWNA Chapter 2 – Radio Frequency Fundamentals

My Study notes from Chapter 2 of CWNA Study Guide

RF Characteristics

  • Wavelength
    • A wavelength is the distance between the two successive crescents (peaks) or two successive throughs (valleys)


  • Frequency
    • Is how often an RF signal cycles in a certain time period
    • Standard measurement of frequency is hertz (Hz). An event that occurs once in a second has a frequency of 1 Hz.
      • 1 Hertz (Hz) = 1 Cycle per second
      • 1 Kilohertz (KHz) = 1000 cycles per second
      • 1 megahertz (MHz) = 1,000,000 (million) cycles per second
      • 1 gigahertz (GHz) = 1,000,000,000 (billion) cycles per second



  • Amplitude
    • The height of the wave.
    • Can be characterised simply as the signal’s strength or power


  • Phase
    • Is not a property of just one signal but instead involves the relationship between two or more signals that share the same frequency.

RF Behaviours

  • Wave Propagation
    • The way the wave moves is known as wave propagation.
    • This can vary drastically depending on the type of material the signal is traversing.
  • Absorption
    • Most common RF behaviour
    • If signal does not bounce off an object, move around an object, or pass through an object, then 100% absorption has occurred.
    • Most materials absorb some RF signal, the amount depends on the material.
  • Reflection
    • Most important RF behaviour to be aware of.
    • Causes serious performance problems in legacy 802.11a/b/g WLANs
    • When wave hits smooth object that is larger than the wave itself, dependant on the material the signal may bounce in another direction.
    • Two Types:
      • Sky wave reflection: Signals below 1 GHz – signal bounces off charged partials in the ionosphere in the earth’s atmosphere.
      • Microwave: 1GHz – 300 GHz, can bounce off smaller objects like a metal door
  • Scattering
    • Described as multiple reflections
    • Is reflection off an object with multiple sides (think mirror ball)
    • Two types:
      • Lower level has lessor effect on signal quality and strength
      • Second type occurs when RF signal encounters some type of uneven surface and is reflected into multiple directions (Chain link fences, wire mesh in stucco walls)
  • Refraction
    • Signal is bent into behaviour known as refraction.
    • when signal passes through a medium with different density thus causing the wave to change direction.
    • Three most common causes:
      • Water Vapour
      • Changes in air temperature
      • Changes in air pressure
  • Diffraction
    • Signal is bent around an object
    • Sitting directly behind the object is an area known as the RF shadow. Depending on the change in direction of the signal this area can become a dead zone of coverage.
  • Loss (Attenuation)
    • Decrease in amplitude
    • Signal may lose strength on the wire or in the air
    • Signal can be absorbed into materials it passes through.
  • Free Space Path Loss (FSPL)
    • Because of the laws of physics the signal will attenuate as it travels despite the lack of attenuation caused by obstructions, absorptions, reflection, diffraction and so on.
    • Loss of signal strength caused by the natural broadening of the waves.
  • Multipath
    • Occurs when 2 or more signals arrive at the receiving station at the same time or within nanoseconds of each other.
    • Four results of multipath
      • Upfade
        •  Multiple RF signal paths arrive at the same time and are in phase (phase differences of 0 to 120 degrees) will cause upfade
        • Results in increased signal strength
      • Downfade
        • Multiple RF signals arrive at the same time but are out of phase (phase difference of 121 to 179 degrees)
        • Results in decrease signal strength
      • Nulling
        • This is signal cancellation
        • Multiple RF signals arrive at the same time and are 180 degrees out of phase of each other
      • Data Corruption
        • Multiple signals arriving but not at the same time the receiver might have trouble demodulating the signal.
  • Gain (Amplification)
    • Increase in amplitude or signal strength
    • Two types:
      • Active – increase to signal on the transmitter or transceivers side through the use of an amplifier. IE more power is applied
      • Passive – done by focusing the antenna, the inner workings of the antenna make the signal stronger.




CWNA Chapter 1 – Wireless Standards, Organizations and Fundamentals

My Notes from chapter 1 of the CWNA study guide

Standard Organisations

Federal Communication Commission (FCC)

  • Regulatory body for the United States for Radio, TV, wire, satellite and cable.
  • Set Rules for what users can do with wireless around:
    • Frequency
    • Bandwidth
    • Maximum power of the intentional radiator (IR)
    • Max equivalent isotropically radiated power (EIRP)
    • Use (indoor / outdoor)
    • Spectrum sharing rules

International Telecommunication Union Radio Communication Sector (ITU-R)

  • Strives to ensure interference free communication on land, air and sea
  • United Nations Tasked the ITU-R with Global Spectrum Management.
  • Broken down into 5 administrative regions and 3 radio regulatory regions

Institute of Electrical and Electronics Engineers (IEEE)

  • Responsible for the creating the standard of how we communicate
  • Best known to IT for its LAN standard the 802 project

Internet Engineering Task Force (IETF)

  • Goal to make the internet work better
  • Known for producing RFCs
  • Many of the protocol standards, best current practices and informational documents produced by the IETF affect WLAN Security

Wi-Fi Alliance (originally named Wireless Ethernet Compatibility Alliance (WECA))

  • Responsible for ensuring Wireless interoperability certification programs
  • The Wi-Fi certification programs are:
    • WMM QOS  mechanisms
    • Helps conserve battery power for devices using Wi-Fi by managing the time the client spends in sleep mode
  • Wi-Fi Protected Setup
    • Simplified and automatic WPA and WPA2 security configs for home and small business.
  • Wi-Fi Direct
    • Enables devices to connect directly without the use of an access point.
  • Converged Wireless Group-RF Profile
    • Defines the performance metrics for Wi-Fi and cellular radios in a converged handset to help ensure that both technologies perform well in the presence of the other.
  • Voice Personal
    • Enhanced support for voice applications in residential or small business Wi-Fi networks. Single AP
  • Voice Enterprise
    • Voice QOS highest priority (Access Category voice AC_VO)
    • Seamless roaming within Enterprise Wi-Fi network (multiple Aps)
  • Tunnelled Direct Link Setup
    • Allows devices to establish a secure link to each other after they have joined a Wi-Fi network
  • Passpoint
    • Designed to revolutionize the end user experience when connecting to a Wi-Fi hotspot. Uses EAP to Auth
    • Also known as Hotspot 2.0
  • WMM-Admission Control
    • Allows Wi-Fi networks to manage network traffic based upon channel conditions, network load and type of traffic (Voice, Video, best effort data or background data)
  • IBSS with Wi-Fi Protected Setup
    • Provides easy config and strong security for ad hoc Wi-Fi networks.
    • Designed for devices with limited user interfaces
    • Feature easy push button or PIN setup, task-orientated short term connections and dynamic networks that can be established anywhere
  • Miracast
    • Seamlessly integrates the display of streaming video between devices.
    • Core Technology and Security
    • Wi-Fi Multimedia
    • WMM Power Save

International Organization for Standardization (ISO)

  • A global nongovernmental organisation that identifies business, government and society needs and develops standards in partnership with the sectors the will put them to use.
  • Responsible for the OSI Model

Communication Fundamentals

Carrier Signals

  • Is a waveform that is modulated (modified) with an input signal for the purpose of conveying information.
  • The carrier signal is usually a higher frequency than the input signal

Keying Methods

  • A Keying method is what changes the signal into a carrier signal.
  • Amplitude-Shift Keying (ASK)
    • Varies the amplitude or height of a signal to represent the binary data
    • When noise occurs it normally affects amplitude of the signal meaning this keying method is more susceptible to signal loss


  • Frequency-Shift Keying (FSK)
    • Varies the frequency of the signal.
    • One frequency can represent the 0 bits and another can represent the 1 bits.

Frequency-Shift Keying.png

  • Phase-Shift Keying (PSK)
    • Varies the phase of the signal
    • A phase change can represent the 0 and no change in phase can represent a 1


Cisco Patch Antenna (AIR-ANT2566P4W-R)

I have had some experience deploying the Cisco AIR-ANT2566P4W-R 2.4-GHz/5-GHz MIMO 4-Element Patch Antenna in both indoor and outdoor environments. One thing that I found was quite a lot of people deploying this antenna didn’t realize that it makes a difference in how you connect up the antenna to the access point. Continue reading “Cisco Patch Antenna (AIR-ANT2566P4W-R)”

Import AP Config (Prime Infrastructure 3.x)

I recently had a requirement to rename approx 700 new APs, update the location and the WLCs. As the location and Name are unique to each AP a normal Prime template would not suffice.

As the APs did not meet the software requirements of 8.2 in order to utilise APIC-EM (which I am keen to trial for pre-staging) I had to look at another method and found the Import AP Config command within Prime Infrastructure would be the best.

The biggest downside to this vs the APIC-EM was is that I need the APs to be online and seen by Prime prior to being able to push the config.

Continue reading “Import AP Config (Prime Infrastructure 3.x)”

CMX Direct Elasticsearch Connector

I recently had the chance to become one of the first people outside of Cisco to setup and configure the CMX to Elasticsearch Connector. Being one of the first meant that the install instructions were not the best, in fact some steps didn’t work at all.
The real benefit of being able to automatically have CMX data collected exported to Elasticsearch for analytical processing, the benefit of using elasticsearch over CMX’s built in reports is the ability to bring in other data sources to cross reference wireless data fields such as username.
Cisco released both a direct connector to elasticsearch and also splunk, I choose to test out the elasticsearch one first.
Below are the steps that I followed to get the Connector passing data from CMX to an Elasticsearch server.

Continue reading “CMX Direct Elasticsearch Connector”

CMX into AWS

UPDATE: I have updated this post as we had to re-deploy a new template into AWS and ran into some issues following the original instructions. The below is working now

As the company that I am working on has a directive from the CIO to go SaaS or Cloud first, I was tasked with attempting to get the current CMX instance into the cloud. Note: Whilst Cisco currently has a CMX Cloud offering, it currently does not support detect and locate feature required to the CMX use case.

Whilst Cisco CMX BU advised me that they (or TAC) would not support the installation process of  CMX into AWS (as AWS do not support OVA deployments), they did advise me that they (and TAC) would support it if the install was successful.  Further to this the CMX BU asked for a list of the steps we needed to under go in order to get it working in AWS.

This Post will advise the steps required to get CMX working within AWS (I would confirm with your Cisco support managers that they will support your install prior to going into production).

The AWS EC2 Instance type that we deployed was the i2.8xlarge due to it was the only EC2 instance that meet all the requirements of the CMX High End specifications. Details of the i2.8xlarge are:

Model vCPU Mem (GiB) Storage (GB)
i2.8xlarge 32 244 8 x 800 SSD

Steps to create CMX image and migrate to AWS (I was given these steps from the Sysadmin team and advised that AWS has provided the powershell app to them)

  1. Import OVA into on premise VMWare environment
  2. Startup the VM
  3. Backup the existing /boot/grub.conf
  4. Cp /boot/grub.conf /boot/grub.conf.bak
  5. vi /etc/grub.conf and delete the first boot entry as this points to a modified linux kernel which aws does like and will make the upload fail

  6. Remove the custom kernel config from the grub.conf entirely
  7. Shutdown the VM
  8. Export the VM to OVA
  9. Steps 9 – 15 were provided by AWS you might need to contact your AWS resources about this for your environment.
  10. Upload to  using EC2 command line tools
  11. Export as OVF from VMWare (this is NOT the option that puts everything into one file). If you already selected the one file option, right click the file under lucy.ocio and select 7-zip → open archive and extract the .vmdk file.
  12. Upload the VMDK using:


  13.  Once you have export the OVA in file format (OVF), open a powershell window server and cd to the directory of the OVF files output
    ec2-import-instance .\is-test05-poc-v1\is-test05-poc-v1-disk1.vmdk --region "ap-southeast-2" --prefix RHEL7AMIv1 -p Linux -t "t2.micro" -f "vmdk" -a "x86_64" --subnet subnet-3fecb55a --instance-initiated-shutdown-behavior stop -b "$S3_BUCKET_NAME" -o "$AWS_ACCESS_KEY" -O "$AWS_ACCESS_KEY" -w "$AWS_SECRET_KEY" -W "$AWS_SECRET_KEY"
  14. Once VM has been uploaded and instance has been created, convert it to AMI
  15.  The upload process may fail. Please just re-run the upload in case there was a problem….
  16. Run the following command to check the status of the upload:
    ec2-describe-conversion-tasks  -O “AWS-access_key” -W “secret-key” --region "ap-southeast-2" 
  17. Once this says it is complete, please allow for up to 30 minutes for the conversion to take place. An easy way to see is looking at the EC2 instance and if it has a “root” volume attached.
  18. Start the amazon instance
  19. Restore the original grub configuration
  20. Cp /boot/grub.conf.bak /boot/grub.conf
  21. Reboot to insure it works
  22. Shutdown instance
  23. Export instance to ami
  24. Share ami with relevant amazon zones
  25. Deploy template and then adjust /etc/hosts (the file has the immutable flag so it can’t be directly edited. We need to unset the flag, then edit it)
    $su -
    $chattr -i /etc/hosts
    $vi /etc/hosts
    $:1,$ s/orginal_hostname/new_hostname/g
  26. This will change the hostname to the new hostname. The reason we need to do this is because the networking is broken so the standard reference points in this file are pointing to something else.
  27. Also ensure the IP address of the hostname is in the hosts file as a fully qualified name
  28. Edit /etc/sysconfig/network – and add the full name of the server
  29. Reboot
    $chattr +i /etc/hosts


Following installation you will need to configure CMX via the WebUI and SSH as you will not have console access within AWS. Please refer to this post for how to do this

You will need to ensure that traffic between the WLCs, Prime is able to access CMX.