voice comm.

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Overview : 

Overview Requirements of VoIP Packet path diversity for low delay VoIP Adaptive multi-stream playout scheduling Internet experiments Demo

Requirements of VoIP : 

Requirements of VoIP Small end-to-end delay for conversational services ( <150ms ) Delay variations (jitter) have to be smoothed using receiver buffer Late packets are lost, no time for retransmissions Small residual packet loss rate is ok Trade-off between end-to-end delay and late loss rate

Packet Path Diversity : 

Motivation for Packet Path Diversity for VoIP In up to 80% better alternative path [Savage ‘99] Multi-path routing [Sidhu ‘91, Bahk ‘92] Uncorrelated packet loss on independent paths [Apostolopoulos ‘01] Efficiency of FEC limited by packet loss and delay correlation [Bolot ‘93, Bolot ‘99] Delay jitter is the major killer of delay sensitive applications Our contributions: Exploitation of statistically independent jitter behavior for VoIP Adaptive multi-stream playout scheduling technique R S Second path 1 2 Speech Packet Path Diversity Default path

Two-path speech coding : 

Two-path speech coding Redundant description of voice stream (MDC) Two bitstreams for two paths Stream 1: [Jiang 2000] Even samples: (8-bit, PCM) Odd samples: (2-bit, ADPCM) Stream 2: Vice versa 25% Overhead Loss of one packet  small reduction in speech quality Loss of both packets  error concealment E s1 s2 O E O E O O E O E O E  E O Packet length Time

Packet Path Diversity for Low Delay VoIP : 

Packet Path Diversity for Low Delay VoIP Time 1 2 3 4 5 6 Sending on path 1 Packet Path Diversity reduces effective delay jitter and therefore late loss rate

Adaptive Playout Scheduling : 

Adaptive Playout Scheduling Adaptive playout scheduling and speech scaling allow us to use more packets for playout at given mean target delay Time 1 2 3 4 5 6 Sending on path 1 If past delay values indicate congestion  delay playout of next packet(s) by stretching speech signal If past delay values are small  advance playout of next packet(s) by compressing speech signal

Modification of Playout Speed : 

Modification of Playout Speed Based on time-domain interpolation algorithm WSOLA [Verhelst et al., 1993, Liang 2001] Original packet Pitch- period 0 2 1 3 4 Template

Adaptive Two-stream Playout Scheduling : 

Adaptive Two-stream Playout Scheduling playout deadline estimate of loss probability Histogram of past delay values Combination of Packet Path Diversity and Adaptive Playout Minimization of Lagrangian cost function Delay Variation of

Internet Experiment : 

Qwest Internet Experiment Explicit path selection using relay server [Apostolopoulos ‘01] UDP packets with payload of 240 bytes Exodus Comm. BBN Planet Netergy Networks 192.84.16.176 MIT 18.184.0.50 Harvard 140.247.62.110 (5ms) (45ms) (40ms) (5ms) (5ms) Sender Relay Server Receiver

Measured Packet Delay Trace : 

Measured Packet Delay Trace Delay in ms Packet number

Adaptive Two-stream Playout Scheduling : 

Adaptive Two-stream Playout Scheduling Delay in ms Packet number

Comparison: Single-path Transmission with FEC : 

Comparison: Single-path Transmission with FEC 2 3 4 1 1 2 3 2 4 1 1 3 2 3 4 1 Stream received with packet loss Stream reconstructed 3 Stream sent Packets protected with FEC  FEC: adds redundancy by sending one or more copies of the source signal in the following packet(s) [Bolot ‘96] FEC protected single-stream For fair comparison Primary copy: quantized at fine resolution (8-bit) Secondary copy quantized at coarser resolution (2-bit) Same data rate as transmission with Packet Path Diversity Same adaptive playout scheduling technique

Results : 

Results delay (ms) Packet loss rate in %

Demo : 

Demo Original Average total end-to-end delay: 84 ms Error concealment: speech segment repetition Path Diversity Single-stream with FEC at same data rate

Conclusions : 

Conclusions Packet Path Diversity for real-time voice communication over IP Multiple Description Coding of speech signal Quality improves with each description received Exploitation of statistically independent jitter behavior Improvement of delay versus speech quality trade-off Adaptive Playout Scheduling Flexible playout deadline using time-scale modification Reduction of late loss rate for given target delay Lagrangian cost function for two-path transmission Internet experiments Implementation of path diversity using relay server Observation of largely independent delay jitter behavior Significant speech quality improvement in comparison to single-path transmission with FEC at the same data rate and end-to-end delay

PESQ Results : 

PESQ Results Perceptual Evaluation of Speech Quality (ITU-T Rec. P.862, Feb. 2001) PESQ can be used for end-to-end quality assessment Ranges from –0.5 to 4.5 but usually produces MOS-like scores between 1.0 and 4.5

Internet Experiment II : 

Internet Experiment II VBNS IP Backbone Service DANTE Operations UUNET Tech. Erlangen 131.188.130.136 Harvard 140.247.62.110 (7ms) (40ms) AT&T (5ms) (5ms) (10ms) New Jersey 165.230.227.81 Path 1 (direct): N. J. – Erlangen Path 2 (alternative): N. J. – Harvard – Erlangen

Result : 

Result Path 1 (direct): N. J. – Germany Path 2 (alternative): N. J. – Harvard – Germany Mean delay 61.3/65.0 ms link loss 0.6% / 1.1% Significant reduction of late loss and end-to-end delay by packet path diversity

Constant Playout : 

Constant Playout Trade-off between packet loss and delay Constant playout deadline late loss

Adaptive Playout : 

Adaptive playout deadline Adaptive Playout Adaptation to delay variation (jitter)

Late Loss  Mean Delay : 

Late Loss  Mean Delay

Speech Scaling : 

Speech Scaling

Demo 2 : 

Demo 2 Original Average total end-to-end delay: 108 ms Path Diversity (PESQ: 4.1) Single-stream with FEC (PESQ: 3.5)

Voice over IP (VoIP) : 

Voice over IP (VoIP) VoIP is rapidly growing 900% 1998-1999 5000% 1999-2004 2004 1999 1998 135 billion minutes 2.7 billion minutes 310 million minutes [Source: IEEE Spectrum, Mai 2000]

Limits of Speech Stretching : 

Limits of Speech Stretching More than 25% is annoying Original Stretching: s=1.3

Speech and Audio Scaling : 

Speech and Audio Scaling Speech scaling Audio scaling original stretched: s=1.3 compressed: f=0.7 original stretched: s=1.3 compressed: f=0.7

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