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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