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Performance Characterization of Voice over Wireless LANs

Performance Characterization of Voice over Wireless LANs. Lionel PEREZ xxxxxx, 2005. Agenda. Introduction to IEEE 802.11 Different MAC mechanisms Quality of Service and 802.11e Related Work How does our solution work? Modelisation Measurements Simulation. Logical Link Control (LLC).

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Performance Characterization of Voice over Wireless LANs

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  1. Performance Characterization of Voice over Wireless LANs Lionel PEREZ xxxxxx, 2005

  2. Agenda • Introduction to IEEE 802.11 • Different MAC mechanisms • Quality of Service and 802.11e • Related Work • How does our solution work? • Modelisation • Measurements • Simulation

  3. Logical Link Control (LLC) Datalink Medium Access Control (MAC) Physical IEEE 802.11 • 1997 • WLAN or Wi-Fi • RFCs • Defines PHY and Data Link Layers

  4. PHY Layer • DSSS • FHSS • Infrared • 802.11 • 802.11b • 802.11g • 802.11a

  5. Data Link Layer • MAC and LLC • LLC • MAC • DCF • PCF

  6. DCF • CSMA CA • Parameters: • DIFS • SIFS • Slot duration • Cwmin • CWmax

  7. PCF • Above DCF • Polling • Parameters: • PIFS • SIFS

  8. Compatibility with Voice • Naive calculation: 85 VoIP calls • In reality, 6 or 7.. 20 ?! • General frame structure • Encapsulation overhead • Intrinsic Overhead • Transmission time

  9. QoS and 802.11e • New MAC Mechanism • HCF • EDCF + EPCF

  10. Related Work • Model, Measure, and Simulate • DCF, PCF and 802.11e • Performance in terms of: • Capacity (Number of connections) • Delay, Jitter, throughput • Voice Quality • Enhancements • Nothing specific to VoIP traffic yet !! (seen as payload in RTP over UDP over IP packets)

  11. Related Work cont’d • In details: • Markov chain • Petri Nets • Entry Parameters: • Cwmin • IFS times • Codec

  12. Alcatel’s solution • Architecture: • Infrastructure mode • Partners: • Aruba • Spectralink • Proprietary protocols and QoS mechanisms • How to measure and predict QoS ?

  13. Traffic Analysis • Identify the QoS mechanism • Modified DCF? Expectations not true • Voice only: • polling (PCF) • Voice + Data: • Ixchariot • PCF • Propose a model

  14. Frame Analysis • Frame structure • Open system • WEP • WPA

  15. Measurement Plan • Open system: • Capacity measurements • Voice + Data: • Voice capacity and Data throughput

  16. Model accuracy • With our QoS scheme (PCF), G.711 • The key factor is framing: 30 ms !!! • Calculations: • Open system capacity • Residual Data throughput • With WEP • With WPA (prioritisation problem)

  17. Thank you.

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