1. Enhancing Conversational Speech Quality of VoIP in a Wired/Wireless Environment Batu Sat and Benjamin W. Wah Illinois Center for Wireless Systems Background Proposed Solutions Results VoIP Providing interactive speech among multiple users Utilizing public and private wired/wireless IP networks Independent of locations of users and devices used IP Networks Long-haul, WAN, LAN wired/wireless networks Non-stationary real-time packet arrivals and losses Large disparity in delay and loss behavior among clients Complex QoS with multiple IP providers and without cost model Quality measured and maintained at end-points Better scalability with end-to-end strategies Conversational Dynamics Different network delays among clients Multiple realities in VoIP in contrast to face-to-face conversation Perception of delays and efficiency affected by conversational switching (turn-taking) frequency Conversational Dynamics & Quality Goals Challenges Design of VoIP End Clients Achieving high and consistent perceptual conversational quality Enabling natural and efficient conversation among users Real-time adaptation to changing network delay & loss conditions Suitable for any communication device using any IP network Quality Metrics No objective metrics for quantifying conversational speech quality Costly non-repeatable subjective tests with full implementation Design of Play-out Scheduling and Loss Concealment Under dynamic packet delays and losses Trade-offs among mouth-to-ear delay (MED), redundancy, and amount of packets not received in time for play-out (UCFLR) Difficulty under dynamic delay spikes and bursty losses With longer MED Improved one-way speech quality Degraded symmetry and efficiency of interactive conversation Trade-off between minimizing pair-wise MED and maintaining a balance among MEDs perceived by users in a conversation Conversational Speech Quality Multiple dimensions in user perception of quality Quality of one-way speech segments Naturalness and rhythm of conversation, mutual-silence durations Trade-Offs Collection of Traces on Delays and Losses Using Planet-Lab nodes for collecting end-to-end traces With packet periods and payloads typical of VoIP applications Modeling of Two-Party and Multi-Party Conversations Utilizing human psychological models when possible Subjective tests to obtain parameters for simulating dynamics Evaluation of Conversational Speech Quality (CSQ) Identification of human-observable and system-measurable metrics Modeling CSQ as function of these metrics Designing human subjective tests Designing Play-out Scheduling/Loss concealment schemes Trade-offs on system measurable and human-observable metrics Schemes for real-time collection and relay of network statistics Schemes for real-time adaptive POS and LCS Face-to-face setting: (A & B’s common perspective) ABAB time VoIP setting: (A’s perspective) (B’s perspective) time A A’B B’A A’B B’ A speaks B speaks A thinks B thinks MED(A  B) MED(B  A) Legend: Public Internet Public Internet Wireles s Private IP Network Trace # JitterLoss 2Low1.7% 5-17% 9High0.1% 10-33% None of the previous algorithms provides consistent balance between one-way speech quality and conversational interactivity Our scheme Hugging delay curve closely Minimizing delay degradations Providing good one-way quality Maximizing human quality perception