CWAP 403 – Start >

I will be summarising each chapter on the Certitrek Publishing – Official Study Guide for CWAP 403 Exam.

I’ve learned plenty of concepts from the first chapter – 802.11 – The Protocol. This is one of the chapters which you have to read and learn. One may not learn the contents of this chapter directly while working or experience this in his/her day today. Following the posts should give you a fair idea of what the chapter entails and get close to fulfilling the exam requirements. You still have to go through the book multiple times and revise the concepts discussed in the CWNA exam to fully grasp the knowledge required for this exam.

OSI Layers

(APSTNDP) – For the purpose of our CWAP exam we will be concentrating our efforts on layer 1-4 only. More so we have to aim at learning layers 1 and 2 as IEEE 802.11 is focussed around them.

IEEE 802.3(Ethernet) & 802.11 (WLAN) operate primarily at Layers 1 & 2 of the OSI model. The Internet Engineering Task Force (IETF) operates at Layer 3 & 4.

Layer 4 is typically TCP/UDP. TCP is a connection-oriented protocol that uses a 3-way handshake, whereas UDP is a connectionless protocol typically used in time-sensitive applications where occasionally dropping packets is better than waiting.

Layer 3 is typically IP with the exception of WAN related protocols like HDLC, ATM, Frame Relay, etc.

Layer 2 (Data Link layer) – This is subdivided into MAC(lower) + LLC (upper). Frames are organized and meaningful collection of bits that are prepended and appended to upper-layer data within the network communications. When Network layer 3 sends data to the Data-Link layer (2), the data is handed off to the LLC and becomes known as MSDU (MAC Service Data Unit). The MSDU consists of data payload that contains the IP packet + some LLC data. When LLC sends the MAC service data unit info to the MAC sublayer, the MAC header information gets added in a MAC Protocol Data Unit (MPDU).

Layer 1 (PHY) – Physical Medium can be RF, Light Waves, Fibre cables. Capabilities include encoding, modulation, demodulation, timing & signals. This layer is subdivided into PLCP (Physical Layer Convergence protocol – Upper) & PMD (Physical Medium Dependent). The PLCP sublayer prepares the frame for transmission by taking the frame from the MAC sublayer and creating the PLCP Protocol Data Unit (PPDU).

802.11 Physical Layers

Protocol Year (adopted) Frequency Channel Width (MHz) MIMO PHY
802.11az Late 2021 60 GHz      
802.11ay 2020 60 GHz 8000 MU-MIMO EDMG
802.11ax Late 2019 2.4 or 5GHz 20,40,80, 160 MU-MIMO HEW
802.11ac wave2 2015 5 GHz 20,40,80, 160 MU-MIMO VHT
802.11ac wave1 2014 5 GHz 20,40,80 SU-MIMOVHT
802.11n 2009 2.4 or 5 GHz 20,40 SU-MIMOHT
802.11g 2003 2.4 GHz 20 N/A ERP
802.11a 1999 5 GHz 22 N/A OFDM
802.11b 1999 2.4 GHz 20 N/A HR-DSSS
802.11 Prime 1997 2.4 GHz 22 N/A DSSS

Modulation is the process of imposing bits on a transmission medium. I have detailed the keying methods useful in understanding the basics of Modulation here. Also, refer to for numbers related to Modulation and Coding. We will be exploring in detail about this in the forthcoming chapters which entail about PHY Layers and Technologies.

Troubleshooting Methods

The industry troubleshooting methods e.g. from Cisco, Microsoft or CompTIA are not tested on the CWAP exam. The CWAP exam objectives list the following troubleshooting actions.

  • Define the Problem
  • Identify the Scale of the Problem
  • Identity Probable Causes
  • Capture and Analyze the Data (Most of the CWAP concentrated here)
  • Observe the Problem
  • Choose appropriate Remedial Steps.
  • Document the Problem and Resolution.

Special Thanks to Rasika as I’ve learned a lot from his blogs.

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.

This 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 the.

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 knowledge.

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 –

Twitterati (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.

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 takes 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 configuration.

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 results 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.

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

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.

The 802.11-2016 standard defines communication mechanism only at the Physical and the MAC sublayer of the Data-Link layer of the OSI model. 

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.

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

Wireless Optimization Tips!

 I have taken into account for a general hospital system where “patient tracking” application is used by doctors and nurses to capture/update patience information.  Patients/Visitors use wireless for their private use along with other hospital staff using wireless network for their day to day work chores. In some instances there might be IoT devices which might include patience monitoring devices/beds which will require seamless wireless network connectivity.

Wi-Fi Optimization

  1. Ensure simulated site survey is conducted for determining the number of AP required
  2. Optimize capacity-in-the-air on existing WIFI infrastructure by enabling more non-overlapping channels, globally reduce AP transmit power levels.
  3. Leverage 5GHz (802.11a/ac) connectivity where possible for critical devices/applications and set SSIDs to single band, preferred. 5GHz has less room for interference when compared to 2.4GHz. Encourage greater use of 5GHz capable devices.
  4. Standardize on common 802.11 data rates to encourage more predictable WIFI connectivity experience and remove 802.11b legacy data rates.
  5. Plan to reduce the overall number of wireless networks. Upto 4 SSID is a good practice.
  6. Set public WIFI SSIDs to 2.4GHz so that they do not interfere with critical 5GHz SSID frequency and clients.
  7. Enable DFS channels UNII2 and UNII-2e will provide greater capacity in the air. Verify site/hospital is not close to Airport/Shipping vessels and Aviation office etc.
  8. Enable 802.11k for optimized roaming on all the possible SSID used.


CCK – Complementary Code Keying
DSSS – Direct Sequence Spread Spectrum
OFDM – Orthogonal Frequency Divisional Multiplexing
FHSS – Frequency Hopping Spread Spectrum

There are various versions of WLAN standard developed to address different data rate and coverage requirements. IEEE 802.11b supports four data rates viz. 1 Mbps, 2 Mbps, 5.5 Mbps and 11 Mbps.
DSSS is used to provide support for 1 Mbps and 2 Mbps data rate.
CCK (to old for CWNA Exam) for 5.5 and 11 Mbps while OFDM is used for higher data rate applications.
OFDM is used in IEEE 802.11a, 11g, 11n, 11ac and 11ad versions. OFDM is employed along with MIMO to increase the data rate further.

CCK is the modulation form used in the 802.11b standard when operating in 5.5 Mbps or 11 Mbps. CCK was chosen because it uses the same approximate bandwidth as MOK and can use the same header and preamble of pre-existing 1 and 2 Mbps wireless networks, thus facilitating interoperability.

FHSS – RF carrier frequency is changed according to the Pseudo-random sequence(PRS or PN sequence). This PN sequence is known to both transmitter and Receiver and hence help demodulate/decode the information. Within one chip duration, RF frequency does not vary. Based on this fact there are two types of FHSS, fast hopped FHSS and slow hopped FHSS. Dwell time usually 400ms, amount of time that a system transmits on a frequency. Hop time is measurement of amount of time taken by transmitter to change from one frequency to another.

DSSS In DSSS, information bits are spread across both frequency and time planes, hence minimizes effect of interference as well as fading. Hence DSSS system prone to errors but at low level compare to FHSS systems. FHSS produces strong bursty errors. DSSS delivers capacity upto 11 Mbps while FHSS supports upto 3 Mbps. DSSS is very sensitive technology while FHSS is very robust technology. This is observed in harsh environment comprising large coverage, noises, collocated cells, multi-path and presence of bluetooth frequency waves etc. DSSS is ideal for point to point applications while FHSS can be used in point to multipoint deployment with excellent performance. 

OFDM  The idea of OFDM is to map complex data on to multiple narrow band subcarriers so that higher data rate can be achieved. The same is shown in the figure. As shown complex modulation scheme such as 16-QAM is first used to map binary data information into complex frequency domain vector form. 16-QAM maps 4 bits on each of the subcarrier. This bunch of subcarriers as per IFFT size are combined and given as input to IFFT block. This block converts frequency domain complex mapper data into time domain data vector. This vector is converted to analog form before being provided as input to RF converter before transmission into the air using antenna.  OFDM solves multipath issues.

CWNA , IEEE 802.11!

  • Hi IEEE 802.11 Key Concepts

Let’s get started with the IEEE 802.11 Journey synopsis. Standards are defined at physical and mac-sub layer(data-link). We are referring to different ways of transmitting data over the air. Also how our communication signal would deliver information. One of the original ones we’ve come across is FHSS (Frequency Hopping Spread Spectrum) and DSSS (Distributed Sequence Spread Spectrum).

In 2007, the IEEE consolidated 8 ratified amendments along with the original standard, creating a single document that was published as the IEEE standard 802.11-2007
The standard covers IEEE standard 802.11-1999, 802.11a.1999, 802.11b-1999, 802.11g-2003,802.11i-2004

802.11b (Sep 1999) is high rate DSSS – Based on 2.4GHz to 2.4835 GHz ISM band
802.11a (Sep 1999) is OFDM (Orthogonal Frequency Divisional Multiplexing) would operate in 5GHz frequency.  There are 3 U-NIII (Unlicensed National Information Infrastructure) frequency bands consisting of 12 channels.
802.11b (1999) – High Rate DSSS, operates in 2.4 GHz frequency. OFDM transmission type and supports BPSK (binary phase shift keying) and QPSK (Quadrature PSK) – 1 & 5.5Mbps and 2 & 11 Mbps. 
802.11g (June 2003) – Speeds upto 54Mbps/works similar to 802.11b in 2.4 GHz. Used a new technology called Extended Rate Physical (ERP) – ISM frequency band.
802.11i (Security) – From 1997 – 2004, not much defined in terms of security in the original 802.11 standard. Three key components of security solution – Data Privacy/Data Integrity/Authentication. This amendment defined a RSN (Robust Security Network).
802.11r-2008 (FT)-  Technology is more often referred to as fast secure roaming because it defines faster handoffs when roaming occurs between cells in WLAN using a strong security defined by RSN.
802.11w (Sep 2009) – IEEE Task Group was a way of delivering management frames in a security manner. Preventing the management frames from being able to be spoofed.802.11 – only on 2.4. Uses hi rate DSSS. It actually came out before 802.11a. Enabled 5.5 and 11Mbps data rates. 22MHz wide channels. Today these rates have become legacy rates. 
802.11n (October 2009) – also known as Wi-Fi 4 is an amendment that improves upon the previous 802.11 standards by adding multiple-input multiple-output antennas (MIMO). 802.11n operates on both the 2.4 GHz and the 5 GHz bands. Support for 5 GHz bands is optional. Its net data rate ranges from 54 Mbit/s to 600 Mbit/s
802.11ac (December 2013) – VTH (Very high throughput, wider channel (20MHz-160MHz) – also known as Wi-Fi 5 is an amendment to IEEE 802.11, published in December 2013, that builds on 802.11n.[28] Changes compared to 802.11n include wider channels (80 or 160 MHz versus 40 MHz) in the 5 GHz band, more spatial streams (up to eight versus four), higher-order modulation (up to 256-QAM vs. 64-QAM), and the addition of Multi-user MIMO (MU-MIMO). As of October 2013, high-end implementations support 80 MHz channels, three spatial streams, and 256-QAM, yielding a data rate of up to 433.3 Mbit/s per spatial stream, 1300 Mbit/s total, in 80 MHz channels in the 5 GHz band
802.11ax ( Sometime in 2019*)  – IEEE 802.11ax also known as Wi-Fi 6 is the successor to 802.11ac, and will increase the efficiency of WLAN networks. Currently in development, this project has the goal of providing 4x the throughput of 802.11ac at the user layer, having just 37% higher nominal data rates at the PHY layer.  More can be read here

While learning about 802.11 PHYs (Physical) I have come across this extremely useful table from cleartosend podcasts/posts as below




Keying Methods

– Amplitude Shift Keying
– Frequency Shift Keying
– Phase Shift Keying
– on-off Shift Keying

Fundamental to all wireless communications is modulation, the process of impressing the data to be transmitted on the radio carrier. Most wireless transmissions today are digital, and with the limited spectrum available, the type of modulation is more critical than it has ever been.

The main goal of modulation today is to squeeze as much data into the least amount of spectrum possible. That objective, known as spectral efficiency, measures how quickly data can be transmitted in an assigned bandwidth. The unit of measurement is bits per second per Hz (b/s/Hz). Multiple techniques have emerged to achieve and improve spectral efficiency.