Evolving Infrastructures for a Nationwide Data Broadcasting Service

Abstract

This paper reviews implementation and operation considerations for supporting a nationwide data broadcasting transmission architecture for non-program-related data. It reviews architectures utilized by PBS National Datacast: VBI, dNTSC, and migration to DTV. Network management requirements to support data delivery are also discussed. For over ten years, PBS National Datacast (NDI) has embedded data streams into existing PBS analog broadcast signals through use of the vertical blanking interval (VBI), and has datacast a variety of multimedia services. Currently NDI delivers data via 260 of the 348 TV transmitters in the PBS system. While VBI has provided a viable option in the past, and continues to provide a niche for certain applications, the data environment today demands more bandwidth; savvy users utilize multiple applications requiring varied types of data. The next step for NDI is implementation of the Dotcast dNTSC (data in NTSC video) technology. The Outcast system uses patent-pending technologies that can inject a 4.5 Mbit/sec digitally encoded data stream into an NTSC broadcast television signal without degrading the signal or interfering with regular television reception. The dNTSC system can make valuable use of existing NTSC assets and provide a smooth transition path to DTV data broadcasting. This paper lays the framework for a data broadcasting architecture where multiple data services contend for a piece of the transport stream, and local data broadcasting opportunities at the station compete with national opportunities for bandwidth.