2001 | OriginalPaper | Buchkapitel
Intrastandard Hybrid Speech Coding for Adaptive IP Telephony
verfasst von : Francesco Beritelli, Salvatore Casale, Mario Francese, Giuseppe Ruggeri
Erschienen in: Quality of Service in Multiservice IP Networks
Verlag: Springer Berlin Heidelberg
Enthalten in: Professional Book Archive
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This paper presents new speech coding issues and algorithms involved in IP telephony. To develop an efficient system of adaptive voice over IP (VoIP), in fact, besides traditional networking aspects, a series of speech processing issues need to be carefully considered. More specifically, two important aspects of discontinuous transmission are dealt with: the impact of the VAD on source throughput and the need for an efficient system of comfort noise. In addition we propose a variable rate, toll quality CS-ACELP coder that uses coding modes compatible with the three 6.4, 8, and 11.8 kbit/s coding schemes standardised by ITU-T in G.729. In particular, the algorithm presents 4 coding categories, with an average bit rate ranging between about 3 and 8 kbit/s, that adapt the rate to changes in network conditions.