Nov. 3, 2000

Adaptive Playout Scheduling in Packet Voice Communications

Group Meeting Talk Yi Liang

Outlines QoS concerns and tradeoffs The jitter adaptation scheme as a

playout scheduling algorithm Setting the playout schedule Packet scaling and loss

concealment Results of listening tests and

performance comparison

Group Meeting Talk Yi Liang

QoS Concerns at the Receiver

Delay Jitter

Delay Packet Loss

Obstructs proper reconstruction of voice packets at the receiver

Impairs interactivityof conversations

Impairs speech quality

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Different Scheduling Algorithms (1)

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QoS Tradeoffs (1)

Playout Jitter

Delay Packet Loss

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Jitter Absorption vs. Jitter Adaptation

Jitter Absorption

Jitter Adaptation

Group Meeting Talk Yi Liang

Different Scheduling Algorithms (2)

1. Method which uses fixed playout time throughout the whole session;

2. Method which estimates delay dynamically but only adjusts playout time during silence periods;

3. Method which dynamically estimates and adjusts playout time, and scales packets within talkspurts using time-scale modification.

Group Meeting Talk Yi Liang

QoS Tradeoffs (2)

Playout Jitter

Delay Packet Loss

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Problems

How to set the playout schedule? How to scale the packet? How does playout jitter affect audio

quality?

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Setting the Playout Schedule

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Packet Scaling

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The Jitter Adaptation Procedure

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Jitter Adaptation

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Loss Concealment

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QoS Tradeoffs (3)

Playout Jitter

Delay Packet Loss

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Three Algorithms under Comparison

1. Method which uses fixed playout time throughout the whole session;

2. Method which estimates delay dynamically but only adjusts playout time during silence periods;

3. Method which dynamically estimates and adjusts playout time, and scales packets within talkspurts using time-scale modification.

Group Meeting Talk Yi Liang

Performance ComparisonTraces

measured between a host

atStanford and

hostsin:

1) Chicago2) Germany3) MIT4) China

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Test on the Quality of Scaled Audio (1)

Three short network traces with different jitter statistics

Six samples are simulated over each trace; Samples are given and evaluated in pairs, in the format of “reference sample – processed sample” to provide higher sensitivity

Eighteen people participated the tests

Score for each condition is obtained by averaging 6x18 ratings

Group Meeting Talk Yi Liang

Test on the Quality of Scaled Audio (2)

5 Degradation is inaudible                          4 Degradation is audible but not annoying3 Degradation is slightly annoying               2 Degradation is annoying                          1 Degradation is very annoying                 

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Quality of Speech Processed by Different Algorithms (1)

Four network traces with different jitter/loss statistics

Four samples are simulated over each trace using two different playout scheduling algorithms (4x2 conditions)

Score for each condition is obtained by averaging all the ratings

Group Meeting Talk Yi Liang

Quality of Speech Processed by Different Algorithms (2)

Quality      Score Excellent      5 Good           4 Fair             3 Poor            2 Bad             1

MNRU (dB)

10 18 24 30 Source

MOS 1.4

2.7

3.6

4.1

4.4

Group Meeting Talk Yi Liang

Conclusions

Small jitter can be traded for lower delay and lower loss rate

Infrequent packet scaling does hardly impair sound quality

Using adaptive scheduling, both delay and loss rate can be significantly reduced – improved overall performance

Being the results of the new tradeoffs …