Publicité
Publicité

Contenu connexe

Publicité

TELE25892-4.3 802.11 MAC Architecture.pptx

  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
Publicité