The document discusses the MAC sublayer in the 802.11n wireless LAN standard. It describes how the 802.11n MAC sublayer aims to improve protocol efficiency, support quality of service standards, and minimize contention overhead through techniques like selective retransmission. It also examines how the 802.11n MAC protocol operates in different modes and addresses problems like hidden and exposed nodes through physical and virtual sensing methods.

1. MAC Sublayer in
WLAN 802.11n
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Presented by
Syed Ahamad
Abhishek Raj
CS252 – Computer Network

2. Outline
 Introduction
 Architecture
 Physical layer
 MAC Sublayer
 Conclusion
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3. References
 Wikipedia
 Text book – Tanenbaum
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4. Introduction
 WLAN – most popular for mobile equipment’s
 Interoperability
 Mobility
 Flexibility
 cost-effective deployment
 Standardize and maintain as IEEE 802.11 by IEEE
LAN/MAN Standards Committee(IEEE 802)
 Established in 1997
 802.11a/b/g
 802.11n
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5. Architecture components
 Stations
 Basic Service set
 Extended Service set
 DS (Distribution System)
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6. WLAN Architecture 6
• Infrastructure
• Ad hoc

7. Factor - 802.11n
 Limited Capacity
 Channel Efficiency
 Multipath
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8. Limited Capacity 8

9. Channel Efficiency 9

10. Multipath 10

11. Key Structure – 802.11n 11

12. RF Signal Fidelity
 Parallel Streams
 Multiple antennas
 Identification of each frame
 Echo cancellation
 Timer setting
 Much reduce frame duplication
 Transmission beam forming
 When receiver is busy – sender finds the best way to
transmit.
 High quality of signal
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13. Physical layer
 Rate adaptation
 802.11b(11Mbps) – spread spectrum method
 Spreading sequence – Barker Sequence
 802.11a(54Mbps) – OFDM method
 But 5 GHz
 802.11g(54Mbps) – OFDM method
 Here 2.4 GHz
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14. Physical layer
 802.11n(100+Mbps) – OFDM and MIMO method
 Bandwidth - 20MHz to 40MHz
 Reduced the framing overhead
 Parallel streams
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15. 15Protocol Stack

16. MAC Sublayer
protocol efficiency
 WMM Mandatory
 WMM – allows AP to control devices
 Assures the quality of service standards
 802.11 – CSMA/CA protocol
 Minimum contention overhead
 Selective retransmission
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17. 802.11 MAC Protocol 17

18. 802.11n MAC Protocol 18
• Mode operation
• DCF(Distributed Coordination Function)
• PCF(Point Coordination Function)

19. Hidden and Exposed
problem
 Transmission Range
 Solution – Physical and virtual sensing.
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20. Virtual Sensing 20

21. Interframe Spacing 21

22. Frame format 22

23. Conclusion
 Limitation
 Spiky and time variant
 Transmission Range
 Power saving – beacon frames
 Trade off
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