test

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
TELE_25892_Princuples of Wreless Networking
2

3. Reference/Reading
 Reading:
 Ch 10 [COL3]
 Reference:
 Most of the slides are taken from the text book
 Web reference:
 See inline
TELE_25892_Princuples of Wreless Networking
3

4. Learning Objectives
 Explain encapsulation of IEEE 802.11 frames
 Explain the phases of Wireless connection formation
 Name and describe various types of roaming
TELE_25892_Princuples of Wreless Networking
4

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
TELE_25892_Princuples of Wreless Networking
5

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
TELE_25892_Princuples of Wreless Networking
6

7. Packets, Frames, and Bits
 Packets
 Data Units at the Network Layer
 Frames
 Data Units at the Data Link Layer
 Bits
 Binary Digits
TELE_25892_Princuples of Wreless Networking
7

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
TELE_25892_Princuples of Wreless Networking
8

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
TELE_25892_Princuples of Wreless Networking
9

10. MAC Protocol Data Unit (MPDU)
 Encapsulates the MSDU
 Is an 802.11 Frame
TELE_25892_Princuples of Wreless Networking
10

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)
TELE_25892_Princuples of Wreless Networking
11

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
TELE_25892_Princuples of Wreless Networking
12

13. Data Link Layer and Physical Layer
Expanded
TELE_25892_Princuples of Wreless Networking
13

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)
TELE_25892_Princuples of Wreless Networking
14
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
TELE_25892_Princuples of Wreless Networking
15

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
TELE_25892_Princuples of Wreless Networking
16

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
TELE_25892_Princuples of Wreless Networking
17

18. Beacon Frame
TELE_25892_Princuples of Wreless Networking
18

19. Passive and Active Scanning
 Passive Scanning Stations Listen for Beacon Frames
 Active Scanning Stations Use Probe Request and Response Frames
TELE_25892_Princuples of Wreless Networking
19

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)
TELE_25892_Princuples of Wreless Networking
20

21. Authentication Frame
TELE_25892_Princuples of Wreless Networking
21

22. Association
 Occurs AFTER Authentication
 Requires Mutually Supported Functions
 Once Associated, Stations can Contend for the Medium and Pass Data
onto the Network
TELE_25892_Princuples of Wreless Networking
22

23. Association Request
TELE_25892_Princuples of Wreless Networking
23

24. Association Reply
TELE_25892_Princuples of Wreless Networking
24

25. Authentication and Association States
TELE_25892_Princuples of Wreless Networking
25

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
TELE_25892_Princuples of Wreless Networking
26

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
TELE_25892_Princuples of Wreless Networking
30

28. Acknowledgement Frame (ACK)
 Every Unicast Frame by the Standard Should be Acknowledged
 Used due to Inability to Detect Collisions
 Provide Delivery Verification
TELE_25892_Princuples of Wreless Networking
31

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
TELE_25892_Princuples of Wreless Networking
32

30. RTS and CTS Frames
TELE_25892_Princuples of Wreless Networking
33

31. Timing Diagram of RTS/CTS
TELE_25892_Princuples of Wreless Networking
34

32. Request to Send / Clear to Send
(RTS/CTS)
TELE_25892_Princuples of Wreless Networking
35

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
TELE_25892_Princuples of Wreless Networking
36

34. Data Frames
 Can be Pure Data
 Can be Null Data
 Can be Combined with other Functions
 Contains the MSDU
TELE_25892_Princuples of Wreless Networking
37

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
TELE_25892_Princuples of Wreless Networking
38

36. Legacy Power Management
TELE_25892_Princuples of Wreless Networking
39

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
TELE_25892_Princuples of Wreless Networking
41

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)
TELE_25892_Princuples of Wreless Networking
42

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.
TELE_25892_Princuples of Wreless Networking
43