It Depends!

This is the landing page for all the wireless related posts on my blog. Majority of the content is towards my study for wireless related certifications like CWNP. The name ‘It Depends!’ is given as  it is the majority of the answers or responses to the wireless queries

CWNA Certification Journey


I managed to get my CWNA certification today, this was my 2nd attempt. The first attempt was a failure a few months ago.

Failed Attempt: 53%

Passed Attempt: 82%

Below are a few tips which I would like to share so that you get most for this certification.

It would be quite beneficial if you already work for a Network/Wireless service provider or Manage wireless network for a company. Being in such a position certainly pays and gives room for joining the pieces of this puzzle.

course will require some monetary investment. I managed to get some
certification videos. Though the videos are for old CWNA course but majority of
the conceptual stuff does not change for new revision. Here is the link >

There are
no video training courses available on CBT nuggets or INE as of today. I did
check with CBT Nuggets via twitter but they do not have any official dates for

So back
to the actual course curriculum. It would be highly beneficial to check the
course outline and objectives -
You can check the differences from CWNA 106 so that you can prepare better

If would
be good a good buy to get the new sybex CWNA official study guide >,miniSiteCd-SYBEX.html

This one
is quite a thick book with over 1000 pages. I guess this book will be used
throughout your career in wireless as a reference guide and a starting point
for everything wireless. Some great work by the 2 David(s) Westcott &
Coleman. When you buy the book you also get online flash cards + practice test
questions valid for 1 year which you can use for further strengthen your

Would be
great and worth downloading the common terms used in the exam/book for the CWNA

I read
almost 1-2 chapters per week. The book might give you a feeling of information
overload every once in a while. Another resource which I used during the
preparation were some podcasts listed below.

  1. CleartoSend -
  2. WLAN Professional -
  3. Packet Pushers -
  4. WiFi for Beginners -

(Twitterverse/Twitter users) - Would highly recommend you to join and follow
the wireless enthusiasts. Thankful to the wireless online community! Many of
them have a vast industry experience and certifications which go a long way in
helping and coaching someone who is new to the wireless domain.

Slack Groups to recommended -

All the
best with your CWNA Study and the Exam! Please buy the exam voucher directly
form CWNP website  (
rather than going directly via PearsonVue. I saved $50USD by doing so.

I am on
to the next Adventure of CWAP and will try and blog more often about the
learnings from the course study.

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QoS Overview

Wireless has somehow made it to the human needs pyramid and has become mission-critical for most of the business around the world. Proper RF and QoS design is the only way to ensure real-time apps have acceptable QoE (Quality of Experience).

The wireless environments are half duplex shared medium they are quite susceptible to collisions. One of the biggest challenges for 802.11 networks is that there is no way to detect that the collision even occured.

802.11e was introduced to bring QoS to Wi-Fi

• EDCA was introduced by IEEE 802.11e in 2005, and has been adopted by the Wi-Fi Alliance as Wireless Multimedia (WMM)
• WMM is now a mandatory part of modern Wi-Fi
• 802.11a/b/g are based on DCF (no QoS) • 802.11n/ac are based on EDCA (QoS is supported)

NOTE: The post describes about QoS in general and can be applied to any networking realm.

Latency, Jitter, and Loss

The quality of a network transmission
is a result of three things:

■ Latency
■ Jitter
■ Loss

Latency is how long it
 for a packet to be received by the endpoint
after it is sent from the source. Latency is also referred to as delay.
Asymmetrical tunneling after a Layer 3 roaming event between controllers can
introduce delay. Again, symmetrical mobility tunneling is the recommended

Delay can be broken into two parts:

■ Fixed delay: The time it takes to encode and decode the packets and the time it
takes for the packet to traverse the network.

■ Variable delay: Caused by network conditions. If the network is highly utilized at
certain times of the day, the variable delay would be higher at those times
than others.

Jitter is the value that
 from the difference in end-to-end latency
between packets. If a packet takes 50 ms to traverse the network and the next
packet takes 100 ms, you have a jitter value of 50 ms.

Loss is simply the ratio of packets that are successfully received by the endpoint to those that were sent by the transmitter.

Correct Packet Marking

Depending on the traffic flow of a packet, traffic can be classified or tagged. This can be used to prioritise the packet thereby impacting the traffic flow. Efforts should be made to ensure that QoS policies are applied end to end which means from WLAN Controller > Core Switch Ports > Access Switch Ports > AP Ports.

Upstream and Downstream QoS

As discussed above, it is important to understand the terminology and direction of the traffic flow to and from the AP and the controller. You have both upstream and downstream QoS:

Radio downstream: Traffic leaving the AP and traveling to the WLAN clients.

Radio upstream: Traffic leaving the WLAN clients and travelling to the AP. Enhanced Distributed Channel Access (EDCA) rules provide upstream QoS settings for WLAN clients

Network downstream: Traffic leaving the controller travelling to the AP. QoS can be applied at this point to prioritize and rate-limit LWAPP/CAPWAP traffic to the AP.

Wi-Fi Multimedia

WMM is a certification that applies to both clients and APs. The features are taken from the 802.11e draft.

Each of the four WMM queues competes for the wireless bandwidth available on the channel. Four queues namely - Background, Best Effort, Video, Voice. WMM uses Enhanced Distributed Coordination Function (EDCF) for handling the queue traffic. If more than one frame from different access categories collides internally, the frame with the higher priority is sent. The lower-priority frame adjusts its backoff parameters as though it had collided with a frame external to the queuing mechanism.

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CWNA - Chapter 2 Summary & Exam Essentials

CWNA Chapter 2 - IEEE 802.11 Standards and Amendments.

“Defined” means the amendment either no longer exists or it was rolled into the existing (or prior versions) 802.11-2007 spec. “Defines” means it is a ratified amendment that will be rolled into 802.11-2011. “Will define” means it is a work in progress and not yet amended.

802.11-1997 (sometimes called 802.11 “prime”) — the original 802.11 specifications included the base functionality along with FHSS and DSSS PHYs.

802.11a — Defined OFDM usage in 5 GHz with data rates up to 54 Mbps.
802.11b —Defined 5.5 and 11 Mbps with HR/DSSS in 2.4 GHz.
802.11c — Defined MAC bridging for 802.11. Was incorporated into 802.1D.

802.11-1999 rolled up 802.11 prime with new enhancements.

802.11d — Defined 802.11 operation in new regulatory domains.
802.11e — Defined QoS
802.11F — Recommended Inter-Access Point Protocol (IAPP) for interoperability of different vendor products. Was not used by anyone and is now withdrawn.

Note: A capital letter designates a recommended practice standalone standard (similar to 802.1X). A lowercase letter designates an amendment to a parent standard. Hence, 802.11F was designed to be a standalone document (and also happened to be a recommended practice), not a part of the full 802.11 standards. This is often a confusing topic in standards naming.

802.11g — Defined ERP PHY, which introduces data rates up to 54 Mbps in 2.4 GHz.

802.11-R2003 rolled up 802.11-1999 and prior amendments, excluding 802.11e.

802.11h — Defined Dynamic Frequency Selection (DFS) for radar detection and avoidance in some 5 GHz bands. Also defined Transmit Power Control (TPC) for managing client transmit power.
802.11i — Defined security enhancements including TKIP, CCMP, and use of 802.1X with WLANs.
802.11j — Defined 4.9 - 5 GHz operation in Japan.

802.11-2007 rolled up 802.11-R2003 with prior amendments.

802.11k — Defines radio resource management processes for RF data collection and sharing.
802.11l — Due to potential confusion between an “l” (letter) and “1” (number), 802.11l was bypassed.
802.11m — Was used as a maintenance amendment that updated inaccuracies, omissions, and ambiguities.
802.11n — Defines High Throughput (HT) PHY with MCS rates up to 600 Mbps in 2.4 GHz and 5 GHz.
802.11o — For similar reasons as 802.11l, 802.11o was bypassed. ‘Is that an “o” (letter) or a “0” (number)? I don’t know, let’s just skip it.’
802.11p — Defines wireless access for the vehicular environment (WAVE).
802.11q — Due to potential confusion with 802.1Q, 802.11q was bypassed.
802.11r — Defines fast BSS transitions (fast secure roaming). Maybe one of these days we’ll use it.
802.11s — Will define 802.11 mesh internetworking.
802.11T — Specified a way to test wireless performance prediction. Remember, capital letters are recommended practices standalone standards. 802.11T was canceled.
802.11u — Will define internetworking with external networks, such as cellular.
802.11v — Will define enhancements for network management.
802.11w — Defines protected management frames to prevent some security vulnerabilities.
802.11x — 802.11 technologies as a whole are often referred to as 802.11x, so this amendment was bypassed.
802.11y — Defines use of OFDM in 3650-3700 MHz.
802.11z —Defines enhancements to Direct Link Setup, which no one uses.
802.11aa — Will define enhancements to video transport streams.
802.11ab —Was bypassed to avoid confusion with devices using 802.11a and 802.11b PHY technologies, which are often abbreviated as 802.11ab.
802.11ac — Will define Very High Throughput (VHT) with gigabit speeds, building on 802.11n MIMO technology.
802.11ad — Will define short range Very High Throughput (VHT) in the 60 GHz spectrum.
802.11ae — Will define enhancements for QoS management.
802.11af — Will define the usage of Wi-Fi in newly opened TV whitespace frequencies.
802.11ag — Similar to 802.11ab, 802.11ag was skipped to avoid confusion with devices using 802.11a and 802.11g PHY technologies, which are often abbreviated as 802.11ag.
802.11ah — Will define the usage of Wi-Fi in frequencies below 1 GHz. Also used as an expression of Wi-Fi pleasure. 802.11…ah!
802.11ai — Will define FILS (fast initial link setup). Designed to address challenges in high-density environments which a large number of mobile users face.
802.11aj - Will define modifications to the IEEE 802.11ad-2012 amendment's PHY and MAC layer to provide support to the Chinese Millimeter Wave (CMMW).
802.11ak - Will define amendment to General Link for use in bridged networks.
802.11aq - Will define delivery of network service information prior to the association of stations on 802.11 networks.
802.11ax - Will define HE(High Efficiency). Expected to be next big PHY enhancement to the 802.11 standards. Operate in both 2.4/5GHz.
802.11ay - Will define improvement of an 802.11ad amendment providing faster speeds.
802.11az - TBC

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CWNA - Chapter 1 Summary & Exam Essentials

Overview of Wireless Standards, Organisations and Fundamentals.

4 Key organisations involved with wireless networking industry

- FCC and other regulatory domains (ITU-R (ACMA (Australia)) (ARIB(Japan)) - FCC regulates communication from/to/within US. Both licensed and unlicensed communications are typically regulated in the following 5 areas 

- Frequency, Bandwidth, Maximum power of the intentional radiator (IR),  Maximum equivalent isotropically radiated power (EIRP), Use (indoor and/or outdoor), Spectrum sharing rules.

- IEEE - 802.11 working group is responsible for creating WLAN standard.

- IETF - International community of people whose goal is to make the internet work better. 

- Wi-Fi Alliance - Global, non-profit organisation of more than 550 member companies devoted in making the wireless communication better. Its main task is to ensure interoperability of WLAN products by providing certification testing.

ISO - international Organisation for Standardisation. 

OSI model - Open Systems Interconnection (APSTNDP)

Application Layer 7- WWW browsers, NFS, SNMP, Telnet, HTTP, FTP
Presentation Layer 6 - Include encryption, ASCII, TIFF, GIF, JPEG, MPEG, etc..
Session Layer 5 -  NFS, NetBIOS names, RPC, SQL
Transport Layer 4 - TCP, UDP 
Network Layer 3 - Provides switching and routing technologies, creates logical paths, known as virtual circuits.
Data Link Layer 2 -The MAC layer and the Logical link control (LLC) layer. IEEE 802.3, ATM, Frame Relay.
Physical Layer 1 - Cables, Ethernet, Fibre, etc.

Communications Terminology 

Simplex - Device is either capable of transmitting or receiving.
Half-Duplex- Capable of transmitting and receiving but not at the same time. Only 1 device can transmit at a time.
Full- Duplex - Capable of transmitting and receiving at the same time.

Radio Frequency Fundamentals 

1. Amplitude - Height, force, or the power of the wave. 
2. Wavelength - Distance between similar points on two back to back waves.

Frequency - Describes a behaviour of waves. How fast the wave travels, or more specifically how many waves are generated over a period of time, is known as frequency.

Phase - is a relative term. It is the relationship between 2 waves with the same frequency

Keying Methods - Some more explanation here.

1. Amplitude-Shift Keying
2. Frequency-Shift Keying
3. Phase-Shift Keying.


1. Know the 4 Industry Organisations
2. Understand core, distribution and access layer
3. Explain the difference between simplex, half-duplex, and full duplex.
4. Understand Wavelength, Frequency, Amplitude & Phase.
5. Keying Methods.

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WiFi Metrics

I am going to pen down a few of the important wireless metrics. This is to access the environment for any concerns and issues raised around the wireless side of things.

So what should we consider a good, acceptable, or poor Wi-Fi signal strength?

-30 dBm - Maximum signal strength, you are probably standing right next to the access point.
-50 dBm - Anything down to this level can be considered excellent signal strength.
-60 dBm - Good, reliable signal strength.
-67 dBm - Reliable signal strength.The minimum for any service depending on a reliable connection and signal strength, such as voice over Wi-Fi and non-HD video streaming.
-70 dBm - Not a strong signal. Light browsing and email.
-80 dBm - Unreliable signal strength, will not suffice for most services.Connecting to the network.
-90 dBm - The chances of even connecting are very low at this level.

RSSI - each device will have different values and output. There’s no defined way to track the RSSI. Client devices take lot of decisions based upon the RSSI. Wifi bars = one of the ways to determine RSSI. It is not always a good factor though as mac OS X tends to show full bars even though only 1 bar or dBm value around -80. Good numbers around RSSI is -67 for voice, typical connections -70. Location analytics tend to be around -60. Values in dBm. Mention website of RSSI.

Image Courtesy : eyesaas

SNR - quality of wireless signal. Level of noise impacts the wireless quality. SNR drives which type of modulation is used. It is not the ratio but different between level of noise and the signal received or broadcasted by the AP. Every vendor calculates SNR differently.

Signal strength vs Noise

Channel utilization - High density environments normally tend to have channel utilization. It reflects the statistics of the environment. How busy our channels are? Also tells when CCI becomes an issue. Turn off some 2.4 radios, lower or higher the power depending on the kind of issue. Data rate - helps in troubleshooting wireless issues. Disable low data rates in the environment. Can disable 1,2, 5.5 data’s rates. Also not advisable to enable high data rate like 24 or 48Mbps.

RETRANSMISSIONS- should not have more than 10% in the environment. Could be caused due to low data rates set in the environment. Hidden nodes can be cause for the issues. Device drivers are also a cause of concern. Retry packet are sent at low data rate. Use Wireshark to track the retry packets. More retires not a healthy environment.

TIMERS- how long does it take the device to associate with AP. One of the metrics to determine. Longer time to join can be an issue. Band steering being enabled 2.4 responses can be delayed and association time will increase. AP that are broadcasting on dfs channels, some client devices do not scan AP on dfs channel. Authentication time also can be slower due to slow responses from radius server. Time to roam can also be factor. This can impact voip/rts traffic.

Limit active SSIDs to <5 : This is a general rule-of-thumb, and should be adjusted based on the vendor/environment and network design and performance requirements. Lower this value even further if you plan on deploying voice over Wi-Fi, perhaps down to 3 or 4 SSIDs max. Useful link

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