Information Technology Reference
In-Depth Information
2
The Design of VoIP Systems with High
Perceptual
Conversational Quality
Benjamin W. Wah and Batu Sat
CoNTENTS
2.1 Introduction .................................................................................................. 42
2.2 Evaluating Conversational Quality........................................................... 47
2.2.1 Previous Work .................................................................................. 47
2.2.2 Evaluations-Generalization of Conversational Quality ............. 49
2.3 Cross-Layer Speech Codecs for VoIP ........................................................ 54
2.3.1 Previous Work on Speech Codecs ................................................. 54
2.3.2 Cross-Layer Designs of Speech Codecs........................................ 58
2.4 Loss Concealments and Play-Out Scheduling ........................................ 59
2.4.1 Previous Work .................................................................................. 59
2.4.2 Packet-Stream Layer LC and POS Algorithms ............................ 61
2.5 Network-Layer Support for VoIP............................................................... 65
2.6 Conclusions................................................................................................... 66
Acknowledgment.................................................................................................. 67
References............................................................................................................... 67
This chapter describes our work on real-time, two-party, and multi-party
voice-over-IP (VoIP) systems that can achieve high perceptual conversational
quality. It focuses on the fundamental understanding of conversational qual-
ity and its trade-offs among the design of speech codecs and strategies for
network control, playout scheduling (POS), and loss concealments. We have
studied three key aspects that address the limitations of existing work and
improve the perceptual quality of VoIP systems. Firstly, we have developed a
statistical approach based on a just-noticeable difference (JND) to significantly
reduce the large number of subjective tests, as well as a classification method
to automatically learn and generalize the results to unseen conditions. Using
network and conversational conditions measured at run time, the classifier
learned helps adjust the control algorithms in achieving high perceptual con-
versational quality. Secondly, we have designed a cross-layer speech codec to
interface with the loss-concealment (LC) and POS algorithms in the packet-
stream layer in order to be more robust and effective against packet losses.
Thirdly, we have developed a distributed algorithm for equalizing mutual
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