Digital Visual Communications over Telephone Networks

Abstract Telephone networks have been evolving for more than a century. Traditional voice communication is expected to be enhanced and eventually replaced by visual communication in the future. This paper addresses two key elements in digital visual communication: video compression and access link technology. Remarkable advances in video compression have come about in just the past few years, especially through international standardization endeavors. For video compression, we review existing and ongoing standards including JPEG, H.261, MPEG1/2, H.26P, MPEG4, and North American HDTV. These standards cover a broad spectrum of applications and are considered the main standards to be used in visual communications. An overview of access technology for POTS, ISDN, HDSL, ADSL, and ATM broadband networks is given. Video coding standards that can be used to transport visual information over these networks are described. Possible future developments for access technology are also discussed.