Nov. 3, 2000 Adaptive Playout Scheduling in Packet Voice Communications

Group Meeting TalkYi 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 TalkYi Liang QoS Concerns at the Receiver Delay Jitter DelayPacket Loss Obstructs proper reconstruction of voice packets at the receiver Impairs interactivity of conversations Impairs speech quality

Group Meeting TalkYi Liang Different Scheduling Algorithms (1)

Group Meeting TalkYi Liang QoS Tradeoffs (1) Playout Jitter DelayPacket Loss

Group Meeting TalkYi Liang Jitter Absorption vs. Jitter Adaptation Jitter Absorption Jitter Adaptation

Group Meeting TalkYi 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 TalkYi Liang QoS Tradeoffs (2) Playout Jitter DelayPacket Loss

Group Meeting TalkYi Liang Problems How to set the playout schedule? How to scale the packet? How does playout jitter affect audio quality?

Group Meeting TalkYi Liang Setting the Playout Schedule

Group Meeting TalkYi Liang Packet Scaling

Group Meeting TalkYi Liang The Jitter Adaptation Procedure

Group Meeting TalkYi Liang Jitter Adaptation

Group Meeting TalkYi Liang Loss Concealment

Group Meeting TalkYi Liang QoS Tradeoffs (3) Playout Jitter DelayPacket Loss

Group Meeting TalkYi Liang 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 TalkYi Liang Performance Comparison Traces measured between a host at Stanford and hosts in: 1)Chicago 2)Germany 3)MIT 4)China

Group Meeting TalkYi Liang 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 TalkYi Liang Test on the Quality of Scaled Audio (2) 5 Degradation is inaudible 4 Degradation is audible but not annoying 3 Degradation is slightly annoying 2 Degradation is annoying 1 Degradation is very annoying

Group Meeting TalkYi Liang 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 TalkYi Liang Quality of Speech Processed by Different Algorithms (2) Quality Score Excellent 5 Good 4 Fair 3 Poor 2 Bad 1 MNRU (dB) Source MOS

Group Meeting TalkYi 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 …