Performance Characterization of Voice over Wireless LANs Lionel PEREZ August 3rd, 2005

Master Thesis Project - Lionel Perez – June 2005 — 2 Project Overview - 1 > Alcatel R&D VoWLAN Team: Aim: Provide a Wireless VoIP Solution Tasks: Validation, Interoperability, Integration Own products + partnerships WLAN Infrastructure: Airespace, then Aruba Wireless IP Phones: Spectralink

Master Thesis Project - Lionel Perez – June 2005 — 3 Project Overview - 2 > Problem: Cost and time intensive systematic tests Capacity Mixed voice and data behaviour Security, Roaming, QoS > Needs: Models, prediction, simulation

Master Thesis Project - Lionel Perez – June 2005 — 4 Project History - 1 > Purpose: Identify key parameters impacting voice quality > bibliographical research (DCF and PCF) > About QoS: no standard!! (802.11e: still Draft) > Temporary solution : Proprietary protocols No information about QoS implementation used

Master Thesis Project - Lionel Perez – June 2005 — 5 Project History - 2 > One doc about the phones: modified MAC layer, DCF based, for QoS > Traffic capture and Analysis: No DCF, more PCF > Define a model > Perform simulation

Master Thesis Project - Lionel Perez – June 2005 — 6 Agenda > Introduction to IEEE > Different MAC mechanisms: DCF and PCF > Quality of Service and e > Related Work > How does our solution work? > Modelisation > Measurements > Simulation

Master Thesis Project - Lionel Perez – June 2005 — 7 IEEE > Late 90’s > Wireless Local Area Network: WLAN (or « Wi-Fi ») > Defines PHY and MAC Layers > Base standard: (802.11: 1997, 2 Mbps) b: 2.4GHz, DSSS 5.5, 11 Mbps Max

Master Thesis Project - Lionel Perez – June 2005 — 8 IEEE > Additional standards for: Higher Data rates: a, g, n Security: i QoS: e (Draft) >

Master Thesis Project - Lionel Perez – June 2005 — 9 PHY Layer > DSSS: Direct Sequence Spread Spectrum > FHSS: Frequency Hopping Spread Spectrum > OFDM: Orthogonal Frequency Division Modulation > Infrared > Widespread products: b: 2.4GHzDSSS11 Mbps g: 2.4 GHzOFDM54 Mbps a: 5 GHzOFDM54 Mbps

Master Thesis Project - Lionel Perez – June 2005 — 10 MAC Layer > Media Access Control: Every node: When am I allowed to talk? > Two modes: DCF PCF > DCF: Distributed Coordination Function Mandatory Best Effort > PCF: Point Coordination Function Optional Real Time

Master Thesis Project - Lionel Perez – June 2005 — 11 DCF - 1 > Best Effort > Carrier Sense Multiple Access / Collision Avoidance

Master Thesis Project - Lionel Perez – June 2005 — 12 DCF - 2 > Parameters: DIFS SIFS Slot duration CWmin CWmax

Master Thesis Project - Lionel Perez – June 2005 — 13 PCF > Optional implementation > Above DCF > For Real time applications > Based on Polling > Parameters: PIFS SIFS

Master Thesis Project - Lionel Perez – June 2005 — 14 Medium Access Times: Summary > Between 10 and 50 µs IFSInterframe Spacing SIFSShort IFSHighest Priority ACK,CTS, Poll Messages and Poll Responses, CF- End PIFSPCF IFS2 nd priorityPCF Operation Mode (Beacon, Retransmitted Poll Messages) DIFSDCF IFS3 rd priorityDCF Operation Mode (back-off, RTS) EIFSExtended IFSLowest priorityAfter detection of erroneous frame

Master Thesis Project - Lionel Perez – June 2005 — 15 Compatibility with Voice > Naive calculation: 85 VoIP calls > In reality, 6 or ?! > General frame structure > Encapsulation overhead > Intrinsic Overhead > Transmission time

Master Thesis Project - Lionel Perez – June 2005 — 16 QoS and e > New MAC Mechanism > HCF > EDCF + EPCF

Master Thesis Project - Lionel Perez – June 2005 — 17 Related Work > Model, Measure, and Simulate > DCF, PCF and e > 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)

Master Thesis Project - Lionel Perez – June 2005 — 18 Related Work cont’d > In details: Markov chain Petri Nets > Entry Parameters: Cwmin IFS times Codec

Master Thesis Project - Lionel Perez – June 2005 — 19 Alcatel’s Solution > Architecture: Infrastructure mode > Partners: Aruba Spectralink > Proprietary protocols and QoS mechanisms > How to measure and predict QoS ?

Master Thesis Project - Lionel Perez – June 2005 — 20 Traffic Analysis > Identify the QoS mechanism > Modified DCF? Expectations not true > Voice only: polling (PCF) > Voice + Data: Ixchariot PCF > Propose a model

Master Thesis Project - Lionel Perez – June 2005 — 21 Frame Analysis > Frame structure > Open system > WEP > WPA

Master Thesis Project - Lionel Perez – June 2005 — 22 Measurement Plan > Open system: Capacity measurements > Voice + Data: Voice capacity and Data throughput

Master Thesis Project - Lionel Perez – June 2005 — 23 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)

Master Thesis Project - Lionel Perez – June 2005 — 24 WLAN Support in OPNET Modeled data rates : 1 and 2 Mbps b: 5.5 and 11 Mbps a and g: 6, 9, 12, 18, 24, 36, 48, and 54 Mbps > Supported physical layers Direct-Sequence Spread-Spectrum (DSSS) Frequency Hopping Spread-Spectrum (FHSS) Infrared light (IR) > DCF MAC operation: Contention based (CSMA/CA) > PCF MAC operation: Poll based

Master Thesis Project - Lionel Perez – June 2005 — 25 Next Points > Perform measurements > Perform simulation: Find relevant models Define the topology What kind of traffic? > Compare and Match the results

Master Thesis Project - Lionel Perez – June 2005 — 26 Thank You.