VoIP over 802.11 Wireless LAN

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VoIP over 802.11 Wireless LAN

• Brandon Wilson
• PI Alexander L. Wijesinha

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(No Transcript)
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Network configuration

• Linksys Cable/DSL Router w/ an 8-port switch
• Cisco Aironet 1200 series Access Point
• 4 Linksys Wireless-G USB adapters (Soft phones on
  Windows)
• 3-Com Wireless PCI adapters on Linux PCs

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Research Objectives

• Obtain a basic understanding of the 802.11
  protocol
• Examine the bandwidth consumption of one VoIP
  call (wireless to wireless)
• Research the effectiveness of the back-off
  algorithm (in the 802.11 standard)
• Look closer at the tradeoff between call quality
  and background traffic throughput

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Making a Call
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Beacons

• Frequency 100ms
• Packet Size 240 bytes
• Beacons/sec 1/.1 10/sec
• (10240 bytes8 bits)/106 0.0192 Mbit / sec

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1 Call Theoretical Bandwidth

• 50 Packets/sec Voice Data ? G.711
• Total bytes to transmit all voice packets (100
  380) (102 158) 221 22654563 bytes/sec
• Theoretical Bandwidth of one call (545638) /
  106 0.436504 Mbit/sec

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TCP Traffic

• FTP Server on the wired LAN and a FTP client on
  the wireless LAN
• Measure bandwidth as only TCP packets and
  corresponding 802.11 acknowledgement packets

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TCP Alone
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TCP with one call
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TCP with two calls
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Average TCP Bandwidth
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UDP Traffic

• UDP packets generated on wireless LAN by
  PackETH
• With each added call, adjust UDP packet delay to
  retain call quality
• Measure Bandwidth as only UDP packets and their
  corresponding 802.11 acknowledgements (ignore all
  other traffic)

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UDP Only
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UDP with one call
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UDP with 2 calls
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Average UDP Bandwidth
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Conclusions

• TCP
• The results of the experiments showed that TCP
  traffic degrades to a significant extent when a
  VoIP call is added to the network
• A possible explanation for the decrease is the
  TCP congestion control mechanism or the access
  point may be giving priority to the VoIP traffic
• 0.85 Mbit / sec drop in TCP Bandwidth which is
  very significant compared to 0.45 Mbit / sec of
  bandwidth require by a VoIP call

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Conclusions contd
UDP Losses in bandwidth are far greater than the
average bandwidth used by a VoIP
call and show that the call, with
assured voice quality, consumes a much greater
portion of the 802.11 bandwidth than
expected 1 call ? 1 Mbit / sec bandwidth
loss 2 call ? 1.5 Mbit / sec bandwidth loss
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Future Work
Future work will consist of repeating the same
experiments on a 802.11g network and looking at
the effects and behavior of the network when the
only variation is the bandwidth is increased by
about a factor of 5