This document discusses the IEEE 802.11 MAC architecture. It describes the frame types, authentication and association processes, and power management techniques in wireless networks. Management frames like beacons are used to broadcast network information during scanning. Authentication establishes the identity of stations, while association allows stations to use network resources. Control frames provide functions like acknowledging frames and protecting transmissions. Power management helps conserve battery life for mobile devices.

1. TELE25892
WIRELESS NETWORK PRINCIPLES
Winter 2023
802.11 MAC Architecture

2. Agenda
 IEEE 802.11 MAC Architecture Elements
 Fames types
 Frame subtypes
 Protection mechanism
 Power management
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3. Reference/Reading
 Reading:
 Ch 10 [COL3]
 Reference:
 Most of the slides are taken from the text book
 Web reference:
 See inline
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4. Learning Objectives
 Explain encapsulation of IEEE 802.11 frames
 Explain the phases of Wireless connection formation
 Name and describe various types of roaming
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5. IEEE 802.11 MAC Architecture Elements
 Packets, Frames, and Bits
 Physical Layer
 Data Link Layer
 802.11 and 802.3 Interoperability
 Three 802.11 Frame Types
 Beacon Management Frame (Beacon)
 Passive Scanning
 Active Scanning
 Authentication
 Authentication and Association States
 Basic and Supported Rates
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6. IEEE 802.11 MAC Architecture Elements
 Roaming
 Reassociation
 Disassociation
 Deauthentication
 ACK Frame
 Fragmentation
 Protection Mechanism
 RTS/CTS
 CTS-to-Self
 Data Frames
 Power Management
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7. Packets, Frames, and Bits
 Packets
 Data Units at the Network Layer
 Frames
 Data Units at the Data Link Layer
 Bits
 Binary Digits
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8. Data Link Layer
 Data Link Layer (DLL) has two sublayers
 Logical Link Control (LLC)
 Establishes Flow control
 Maintains Flow Control
 Media Access Control (MAC)
 802.11 Specified Operations
 Where the MAC address resides
 MAC Service Data Unit (MSDU)
 Data portion of MAC coming from LLC
 MAC Protocol Data Unit (MPDU)
 After encapsulation in MAC frame
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9. MAC Service Data Unit (MSDU)
 Contains Data From Layers 3-7 and the LLC
 The Data Payload
 Only Data Frames Carry the MSDU
 Maximum Size of 2,304 bytes
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10. MAC Protocol Data Unit (MPDU)
 Encapsulates the MSDU
 Is an 802.11 Frame
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11. Physical Layer
 Has two Sub-Layers
 Physical Layer Convergence Protocol (PLCP)
 Physical Media Dependent (PMD)
 PLCP Services Data Unit (PSDU)
 PLCP Protocol Data Unit (PPDU)
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12. PLCP Data Units
 PLCP Services Data Unit (PSDU)
 The Same Frame as the MPDU
 PLCP Protocol Data Unit (PPDU)
 Adds Preamble and PHY Header
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13. Data Link Layer and Physical Layer
Expanded
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14. 802.11 and 802.3 Interoperability
 802.3 Frames are encapsulated within 802.11 frames for Transmission
 802.3 standard frame Max. Size = 1,518 bytes
 802.11 standard frame Max. Size = 2,347 bytes
 802.11 has four address field in header
 Possible addresses are
 Receiver Address (RA)
 Transmitter Address (TA)
 Basic Service Set Identifier (BSSID)
 Destination Address (DA),
 Source address (SA)
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802.11 MAC header

15. 802.11 Frames
 Frame Types
 Management Frame
 Control Frame
 Data Frame
 All have many Sub-Types
 All are Identified by Frame Control Field of the Frame Header
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16. Management Frames
 Association request, and response
 Reassociation request and response
 Probe request, and response
 Beacon
 Announcement Traffic Indication Message (ATIM)
 Disassociation
 Authentication, and Deauthentication
 Action
 Action No ACK
 Timing advertisement
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17. Beacon Frame
 Beacon Frame content
 Time Stamp
 Parameter Sets
 Channel Information
 Data Rates
 BSS Capabilities
 SSID
 TIM and DTIM
 QoS Capabilities
 Security Capabilities
 Vendor Proprietary Information
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18. Beacon Frame
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19. Passive and Active Scanning
 Passive Scanning Stations Listen for Beacon Frames
 Active Scanning Stations Use Probe Request and Response Frames
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20. Authentication
 Stations Must Authenticate to Begin Connection with an AP
 Failed Authentication is the #1 Cause of Failed Association
 Many Authentication Methods Exist
 Open (no credentials required)
 Shared key (uses WEP key)
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21. Authentication Frame
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22. Association
 Occurs AFTER Authentication
 Requires Mutually Supported Functions
 Once Associated, Stations can Contend for the Medium and Pass Data
onto the Network
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23. Association Request
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24. Association Reply
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25. Authentication and Association States
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26. Basic and Supported Data Rates
 Basic Rates are the MANDITORY Data Rates of the BSS
 Supported Rates are the OPTIONAL Data Rates of the BSS
 Information is Found in the Beacon Management Frame
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27. Control Frame
 Power Save Poll (PS-Poll)
 Request to send (RTS)
 Clear to send (CTS)
 Acknowledgment (ACK)
 Contention Free-End (CF-End)
 CF-End + CF-ACK
 Block ACK Request (BlockAckReq)
 Block ACK (BlockAck)
 Control wrapper
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28. Acknowledgement Frame (ACK)
 Every Unicast Frame by the Standard Should be Acknowledged
 Used due to Inability to Detect Collisions
 Provide Delivery Verification
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29. Protection Mechanisms
 Request to Send / Clear to Send (RTS/CTS)
 Clear to Send to Self (CTS-to-Self)
 Help Combat Hidden Node Issues
 Allows Mixed Mode Operations
 Creates Additional Overhead
 Frames Sent at Lowest Basic Rate
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30. RTS and CTS Frames
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31. Timing Diagram of RTS/CTS
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32. Request to Send / Clear to Send
(RTS/CTS)
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33. Clear to Send to Self (CTS-to-Self)
 Less Overhead than RTS/CTS
 From the Station to Itself
 Used in Mixed Mode BSS Operations
 Creates Additional Overhead
 Frames Sent at Lowest Basic Rate
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34. Data Frames
 Can be Pure Data
 Can be Null Data
 Can be Combined with other Functions
 Contains the MSDU
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35. Power Management
 Conserves Battery Life
 Require use of TIM (Traffic Indication Map), DTIM or ATIM
 Two Modes Used
 Active Mode (Always On)
 Power Save Mode (On and Off)
 Legacy Power Save Still used
 WMM-PS Used on Newer Devices
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36. Legacy Power Management
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37. Summary
 In this lesson we reviewed the concept of encapsulation and decapsulation
 We studied the fields of MPDU and relationship between MPDU and PPDU
 We studied the IEEE 802.11 frame types
 We studied the different types of management frames used in IEEE 802.11
standard
 We studied how authentication and Association are performed in IEEE
802.11
 We studied how roaming takes place
 We studied where fragmentation can be useful and where it add overhead
 We studied various types of control frames and the use of
acknowledgement as well as RTS-CTS and CTS-to- self messages
 We studied power management features of IEEE 802.11 and how
interoperability can be achieved while power saving mode is being used by
the clients
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38. Key Terms
 Beacon
 RTS/CTS
 Traffic indication map (TIM)
 Delivery traffic indication message (DTIM)
 Announcement traffic indication message (ATIM)
 WMM Power Save (WMM-PS)
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39. Some Sample Questions
 Describe the main functions of the sublayers in data link layer and
physical layer of 802.11 MAC architecture.
 What are the four addresses in 802.11 MAC frames?
 With a flow diagram, mention the states of authentication and
association in 802.11.
 What are the three types of frames in 802.11? Briefly describe the
functions/purpose of each. Give some examples of each.
 List some important information you find in a beacon frame.
 What is the difference between active scanning and passive scanning?
 Explain why every unicast frame in 802.1 1 requires
acknowledgement.
 With a diagram, explain why and how RTS/CTS mechanism is used in
802.11.
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