wlan 802.11n - mac sublayer
TRANSCRIPT
MAC Sublayer in
WLAN 802.11n
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Presented by
Syed Ahamad
Abhishek Raj
CS252 – Computer Network
Outline
Introduction
Architecture
Physical layer
MAC Sublayer
Conclusion
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References
Wikipedia
Text book – Tanenbaum
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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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Architecture components
Stations
Basic Service set
Extended Service set
DS (Distribution System)
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WLAN Architecture 6
• Infrastructure
• Ad hoc
Factor - 802.11n
Limited Capacity
Channel Efficiency
Multipath
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Limited Capacity 8
Channel Efficiency 9
Multipath 10
Key Structure – 802.11n 11
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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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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Physical layer
802.11n(100+Mbps) – OFDM and MIMO method
Bandwidth - 20MHz to 40MHz
Reduced the framing overhead
Parallel streams
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15Protocol Stack
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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802.11 MAC Protocol 17
802.11n MAC Protocol 18
• Mode operation
• DCF(Distributed Coordination Function)
• PCF(Point Coordination Function)
Hidden and Exposed
problem
Transmission Range
Solution – Physical and virtual sensing.
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Virtual Sensing 20
Interframe Spacing 21
Frame format 22
Conclusion
Limitation
Spiky and time variant
Transmission Range
Power saving – beacon frames
Trade off
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