Quality of VoIP service in todays Internet

1
Quality of VoIP service in todays Internet

• Athina Markopoulou, Fouad Tobagi
• SNRC Retreat
• 11/15/01

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System under evaluation approach
3
Measurements
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Voice Quality Classes
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Emodel

• Computational model (ETSI, ITU G.107, G.108,
  G.113, G.114)
• Use it as a framework to bring all impairments
  together
• R (Ro-Is) - Id(echo, m2e delay) Ie(codec,loss)
  A

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Loss impairment

• The starting point Ie(loss0) depends on the
  Codec.
• The curve Ie(loss rate) depends on the
  parameters
• codec, PLC, loss model (bursty/uniform, packet
  sizeunit of loss)
• Combine data from the following sources Emodel,
  R.Cox, S.Voran, J.Gruber

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Delay Impairment

• Consists of echo Id_echo and interactivity Idd
  impairments
• Id(task, EL, m2e)Idd(task, m2e)Id_echo(EL, m2e)

• Notation
• EL Echo loss (dB)
• Task type of conversation 1,..6
• References
• Kitawaki, Emodel

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Time varying quality of a call

• Telephone calls last several minutes both Ie and
  Id may vary with time
• Recency effect perceived vs. theoretical Ie.
• Overall rating at the end of the call

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Example call

• 15min (1400- 1415), Wed 06/27/01
• From Thornton, CO, to AshburnVA

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Performance of example paths

• Example of an inherently bad path for VoIP
• 30 of the calls have MOS lt 3.6
• under the most tolerant assessment

• Example of a potentially operational path for
  VoIP
• only 6 of the calls have MOS lt 3.6
• if the adaptive playback is appropriately tuned

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Improving adaptive playout to maximize MOS

• Objective so far to follow the trace as closely
  as possible
• Problems
• Overshooting a la TCP over-estimates the delay
• Exiting spikes slow moving average often
  under-estimates the delay (loss)
• Very sensitive to the tuning of the parameters
• New scheme
• Include explicitly the delay impairment into the
  objective maximize MOS(delay, loss)
• Do not follow closely the trace overestimate
  the delay up to the interactivity threshold

q
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Example results from improved playout

• Baseline playout for adapting per talkspurt
  R.Ramachandran, J.Kurose, D.Towsley,
  H.Schulzrinne, Adaptive playout mechanisms for
  packetized audio applications in wide-area
  networks, Infocom 1994.
• Baseline playout sensitive to tuning (weights,
  ENTER/EXIT spikes)
• Here we show in red a reasonably tuned baseline
  playout it still fails sometimes