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A Case for WiFi Relay: Improving VoIP Quality for WiFi Users

A Case for WiFi Relay: Improving VoIP Quality for WiFi Users. Amit Mondal, Northwestern University Cheng Huang , Microsoft Research Jin Li, Microsoft Research Manish Jain, Akamai Aleksandar Kuzmanovic, Northwestern University. Booming of Unified Communications.

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A Case for WiFi Relay: Improving VoIP Quality for WiFi Users

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  1. A Case for WiFi Relay: Improving VoIP Quality for WiFi Users Amit Mondal, Northwestern University Cheng Huang, Microsoft Research Jin Li, Microsoft Research Manish Jain, Akamai Aleksandar Kuzmanovic, Northwestern University

  2. Booming of Unified Communications • Attending meeting in person is nice, but the overhead due to travel is high • SEA  CPT • Planned: ~24 hours • Actual: ~42 hours • Unified Communications promises • VoIP service double in next 4 years, with an annual growth rate of 26% (InfoneticsResearch, 2008) not being there, but better than being there

  3. Booming of Unified Communications • Widely validated in the consumer world • Gradually being adopted by enterprises • Cisco acquired WebEx • Google announced acquisition of GIPS, which powers • Microsoft Unified Communications

  4. Problem due to WiFi • Large number of WiFi users in enterprises • more than 43% enterprises provide only WiFi connections to their employees • 36% of organizations use VoIP over WiFi VoIP calls using WiFi significantly worse than those not (field data from Microsoft UC system)

  5. SureCall and WiFi Relay • SureCall • a measurement and experiment platform • understand problems and experiment solutions • WiFi Relay • a simple application-layer solution to improve VoIP QoS over WiFi

  6. SureCall Platform • A distributed measurement and experiment platform • Agents are installed on volunteers’ machines • Measurements and experiments driven by a master • Deployment status • 80 unique machines • across geographical regions, enterprises and homes • SureCall VoIP measurement • Emulated voice sessions • 5-minute (per hour), 50 fps (20 msgap), 60 byte packet • Detailed packet-level traces collected

  7. Impact on WiFi links of VoIP WiFi links can significantly degrade VoIP performance

  8. Effectiveness of Redundancy • Passive analysis with voice packet replication • Replication ratio r = 2, 3, 4 or 5 Packet losses can be effectively mitigated using application layer packet replication

  9. Overhead of Replication • Typical voice packet size = 60 bytes • Encapsulated with RTP (12 bytes), UDP (8 bytes), IP (20 bytes), 802.11 MAC (28 bytes), PHY (20 us for 802.11g) headers • Airtime • DIFS + PHY header + ((60 + 76 bytes) / 54Mbps) = 70 us Replicating audio packet at application layer causes only marginal increase in air time

  10. WiFi Relay Solution • Nearby wired endpoints as relays • Heavy replication between relays and wireless endpoints • No dedicated infrastructure

  11. Evaluation • Evaluated on the SureCall platform • Upgrade SureCall agents to support relay • Simultaneous direct and relayed VoIP calls between each pair of SureCall agents • apple-to-apple comparison • Relay node selection based on enterprise internal location database

  12. Improvement with WiFi Relay WiFi Relay greatly reduces packet loss

  13. Improvement with WiFi Relay • Mean Opinion Score (MOS) • Calculated from packet loss rate and jitter (Cole et al., CCR 2001) • Fixed de-jitter buffer of 100 ms WiFi Relay significantly improves VoIP quality for WiFi users

  14. Conclusion • WiFi links greatly degrade VoIP quality • Application layer packet replication is an effective way to mitigate packet loss • WiFi Relay significantly improves VoIP quality Cape Town: attend in person Elsewhere: use WiFi Relay

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