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

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
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
VoIP calls using WiFi significantly worse than
those not (field data from Microsoft UC system)

• 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

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
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

Replication Ratio Air Time (us)
1 70
2 79
3 87
4 96
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