Certified Wireless Network Administrator (CWNA)PW0-105

Chapter 12WLAN Troubleshooting

Chapter 12 Overview

• Layer 2 Retransmissions• 802.11 Coverage Considerations• Voice vs. Data• Performance• Weather

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Layer 2 Retransmissions

• Retransmissions occur when the sending STA does not receive an ACK frame from the target STA

• Layer 2 retransmissions impact performance– Increase overhead– Increase latency and jitter

• Real-time applications are impacted most by retransmissions– All communications are slower

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Layer 2 Retransmissions Causes

• RF Interference• Multipath• Adjacent Channel Interference• Low SNR• Mismatched Power Settings• Near/Far• Hidden Node

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RF Interference

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Multipath

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Adjacent Channel Interference

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Low SNR

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Mismatched Power Settings

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Near/Far

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Hidden Node (Obstruction)

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Hidden Node (Large Coverage Cell)

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Hidden Node (Distributed Antenna System)

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Hidden Node (RTS/CTS)

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802.11 Coverage Considerations

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• Dynamic Rate Switching (DRS)

• Roaming– Layer 3 roaming

• Co-channel interference

• Channel Reuse/Multiple Channel Architecture (MCA)

• Single Channel Architecture (SCA)

• Capacity vs. Coverage

Voice vs. Data

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Performance

• Transmission power rates

• Antenna gain• Antenna type• Wavelength• Free space path loss• Physical environment• CSMA/CA

• Encryption• Application use• Number of clients• Layer 2

retransmissions

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Weather

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• Lightning

• Wind

• Water

• Air stratification

• UV/Sun

Chapter 12 Summary

• Layer 2 Retransmissions• 802.11 Coverage Considerations• Voice vs. Data• Performance• Weather

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