Wireless LAN(WLAN) or Wi-Fi devices as they are normally termed have pervaded our day to day life. Whenever we connect to the internet at home/public places or even at offices – we normally use a Wi-Fi router to connect our devices (may it be a pad/smart-phone or laptop) to the internet.

The Following set of articles are published to help a WLAN developer understand the different features of the WLAN standard (802.11). It touches upon various WLAN concepts such as association, authentication, encryption, roaming, Data aggregation etc.

Since i have mostly worked as an 802.11 Medium Access Layer (MAC) Engineer in my long career – most of the articles delve into the MAC Layer concepts of the Wi-Fi standard.

Table of contents

• Introduction to WLAN
• Introduction to WLAN – Part 2
• Introduction to WLAN – Part 3
• WLAN Standards
• WLAN Network Topologies
• Beacons Explained
  • Contention for Medium by AP to transmit Beacon
  • Beacon Transmission in IBSS Mode
  • Beacon Frame Format
• Association to an Access Point – part 1
• Associating to an Access Point – part 2 (wireless captures)
• Wireless Authentication and Data Security
• WLAN Open System Authentication
• WLAN Shared Key Authentication
• WEP Encryption
  • WEP Encryption – Key Mapping Keys
  • WEP Key Size and Initialization Vector
  • WEP MPDU Format
  • WEP Encapsulation
  • WEP Decapsulation
  • Problems in WEP Encryption
• 802.1X Authentication and Data Security Enhancements
  • Understanding WPA and WPA2 
    • WPA Information Element
  • RSN Information Element
  • 802.1X and Pre-shared Key (PSK) Authentication
  • WLAN Association for 802.1X- Pre-shared Key (PSK) Mechanism
    • 802.1X – Generation of Master Key
    • Pre-Shared Key (PSK) Mechanism – Generation of Master Key
    • EAPOL 4-way Handshake
    • Security Association Contexts
    • Wireless Capture Example – Pre-shared Key (PSK) – Part 1
    • Wireless Capture Example – Pre-Shared Key (PSK) – Part 2
  • Wlan EAP exchange – 802.1X EAP packet exchange – Part 1
  • WLAN EAP Exchange – 802.1X EAP packet exchange – Part 2
  • WLAN EAP Exchange – 802.1X EAP packet exchange – Part 3
• Pre-Authentication in WLAN
• PMKID Caching
• Opportunistic Key Caching
• TKIP Encryption Mechanism
  • TKIP Encapsulation
  • TKIP Decapsulation
  • TKIP MIC – Need and MIC Format
  • TKIP Replay Protection
• AES Encryption Mechanism
  • AES Encapsulation
  • AES Decapsulation
• Distributed Co-ordination Function (DCF)  
  • Backoff Mechanism in WLAN
  • Contention Window and NAV Timer
  • DCF Timing Relationships
• Point Co-ordination Function (PCF)
• Drawback of DCF Mechanism and development of EDCF and HCF 
• Packet User Priority
• 802.1p priority in ethernet frame
• 802.1p mapping to 802.11 (WMM) Quality of service
• Enhanced Distributed Co-ordination Function (EDCF) – Part 1
• Enhanced Distributed Co-ordination Function (EDCF) – Part 2
• EDCF Information Elements – Part 1
• EDCF Information Elements – Part 2
• Hybrid Co-ordination Function (HCF)
• Power Save in WLAN – Legacy Power Save
  • Traffic Indication Map (TIM) Explained
  • Traffic Indication Map (TIM) Bitmap calculation
  • Legacy Power Save – PS-POLL Mechanism
• WMM Unscheduled Automatic Power Save delivery (U-APSD) 
  • Access Point behaviour in U-APSD
  • Delivery Enabled U-APSD
  • Trigger Enabled U-APSD
  • Understanding ADDTS Add Traffic Stream for U-APSD
• Understanding Transmit Opportunity (TXOP)
• Introduction to Block ACK
  • Block ACK Mechanism Session Negotiation
  • Block ACK Frame Formats – ADDBA Request Frame
  • Block ACK Frame Formats – ADDBA Response Frame
  • Block ACK Frame Formats – DELBA Frame
  • Block ACK Frame Formats – Block ACK Request
  • Block ACK Frame Formats – Block ACK
• Regulatory Requirements in 802.11
  • Country Element – operating extension identifier < 201
  • Country Element – operating extension identifier > 201
  • Station operation when entering a new Regulatory domain
  • Dynamic Frequency Selection (DFS) in WLAN
  • Access Point detection of DFS signal and operation
  • Extended Channel Switch Announcement and Its usage
  • Radar Signals and its signatures
  • Radar Signal Detection method in Network driver
• The Advent of Multi-Input-Multi-Output(MIMO)
• Channel Bonding
  • Channel Bonding – 802.11n
  • Channel Bonding – 802.11ac
  • Channel Centre Frequency Calculations – 802.11ac
• MCS Rates in 802.11n
• MCS Rates in 802.11ac
• Aggregation in 802.11
  • A-MSDU Aggregation
  • A-MPDU Aggregation
    • A-MPDU Parameters
  • 802.11n High ThroughPut (HT) Immediate Block ACK
  • 802.11n High Throughput (HT) Delayed Block ACK
  • Compressed Block ACK Bitmap
  • Partial State Information and Full State Information for Compressed Block ACK
• co-existence between 20/40 MHz Stations in 2.4 GHz 
• 20/40 BSS Co-existence Elements and 40 MHz Intolerance bits
• 802.11n High Throughput (HT) transmission modes
• HT Protection and OBSS Protection
• 802.11 PLCP Frame Formats
  • 802.11b PLCP Frame Format
  • 802.11g PLCP Frame Format – Part 1
  • 802.11g PLCP Frame Format – Part 2
  • 802.11g PLCP Frame Format – Part 3
  • 802.11a PLCP Frame Format 
  • 802.11n PLCP Frame Format
  • 802.11ac PLCP Frame Format – Part 1
  • 802.11ac PLCP Frame Format – Part 2
  • 802.11ac PLCP Frame Format – Part 3
• Transmit BeamForming in 802.11n and 802.11ac
  • Channel sounding for Transmit Beamforming
  • Implicit Feedback and Explicit feedback for Transmit Beamforming
  • Explicit Transform Beamforming feedback methods
  • Transmit Beamforming Capabilities fields
  • 802.11ac Explicit Transmit Beamforming
• TX-VECTOR and RX-VECTOR
• Spatial Multiplexing Power-save (SMPS)
  • Dynamic SMPS and Static SMPS
  • Spatial Multiplexing Power Save Action Frame
• Reverse Direction Grant Protocol
  • Reverse Direction Grant Protocol explained
• Management Frame Protection
  • Management Frame Protection – Frame Parameters
  • Management Frame Protection – IGTK
  • Management Frame Protection – understanding BIP – Part 1
  • Management Frame Protection – understanding BIP – Part 2
  • Security Association Teardown Protection – Part 1
  • Security Association Teardown Protection – Part 2
• Introduction to 802.11ax (WiFi 6/e)
  • Major PHY related changes in WiFi 6
  • Resource Units in 802.11ax
  • Trigger Frames in 802.11ax
  • Basic Trigger Frame in 802.11ax
  • MU-RTS Frame in 802.11ax
  • Buffer Status Reports (BSR) – Unsolicited BSR
  • Buffer Status Reports (BSR) – Solicited BSR
  • Down Link Multi-User OFDMA in 802.11ax
  • UpLink Multi-User OFDMA in 802.11ax
  • Co-Channel Interference and BSS coloring
  • Inter-BSS and Intra-BSS PPDU
  • Dual NAV Operation
  • Spatial Reuse Operation
    • Spatial Reuse Groups (SRGs)
    • Identifying packet received as SRG or non-SRG PPDU
    • OBSS Packet Detect Threshold Spatial Reuse
    • OBSS PD Non-SRG Packet Procedures in 802.11ax
    • OBSS PD SRG Packet Procedures in 802.11ax
    • OBSS PD Level Requirements for OBSS PD operation
    • Transmit Power Restriction period and TX power level for OBSS PD operation
    • OBSS PD Example Operation
    • PSRR PPDU and PSR-based Spatial Reuse
    • PSR-based Spatial Reuse Operation – MAC settings 
  • Target Wake Time in 802.11ax
    • Target Wake Time – HE MAC Capabilities Settings
    • TWT Element, TWT Information Field and TWT parameter set Field
    • TWT Setup Command and Flow Type description
    • Example Operation for Individual TWT and Broadcast TWT

Introduction to WLAN