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% ( Infonetics Research, 2008 ) not being there, but better than being there

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

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) 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 ms gap), 60 byte packet – Detailed packet-level traces collected

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

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

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 Replication RatioAir Time (us) 170 279 387 496 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. Impact of Relay on Jitter Relay has negligible impact on end-to-end jitter

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

14. 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

15. 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 Cape Town: attend in person Elsewhere: use WiFi Relay