1.7 Technologies

1.7.1 Forms of Interactivity

The technologies that render the TV interactive enable both local and remote interactivity . Whereas remote interactivity relies on an Internet Service Provider (ISP) to produce responses to viewer's commands, local interactivity relies on the receiver to respond without reaching to the Internet. Local interactivity implies downloading and executing interactive content locally, by the receiver, and enables customizing a single uniform broadcast to the individual preferences of millions of viewers . Remote interactivity implies converting viewers' commands into messages sent over the Internet, or other return channel technologies (e.g., the Quadrature Phase Shift Keying (QPSK) return channel used by Cable providers) and subsequently transforming responses received (e.g., HTML pages) for display.

1.7.2 Content Transport Technologies

This book surveys and presents two types of content transport technologies: MPEG-based and IP-based. MPEG-based transport techniques are best suited for over-the-air broadcasts, as well as for noisy cable transmissions. IP-based technologies are best suited for controlled transmission environments such as electromagnetically sheltered cables.

1.7.2.1 MPEG

The Moving Picture Expert Group (MPEG) 2 Standard, ISO/IEC 13818, for encoding and decoding of audio and video streams, developed the Digital Storage Media Command and Control (DSM-CC) ISO/IEC 13818 Part 6 standard for the delivery of multimedia broadband services. The initial charter of the DSM-CC group was driven by the need for a trick-mode standard, allowing the replay of content at various speeds. This work has evolved into a generic data delivery mechanism capable of broadcasting file systems. Of specific interest for iTV broadcasting is the specification of the DSM-CC data and object carousels protocols. A carousel is a chunk of structured data that is transmitted periodically, to allow receivers that tune at random intervals during the transmission to acquire the data.

The primary advantage of MPEG data delivery over IP-based delivery is robustness in noisy environments. To deliver data (in addition to audio and video) using MPEG-2, the data is fragmented into packets. To place the data within those packets, a rich library of encapsulation methods is available to render the transmission reliable even in the noisiest environments.

1.7.2.2 IP

The IP is concerned with two basic issues: addressing and fragmentation. Addresses are used to identify data transmitters and receivers. On transmission, data is fragmented into small packets and transmitted over small packet networks. Participants in an IP network are referred to as hosts , each of which must have software or hardware modules that know how to receive, send, and process IP packets, also known as Internet datagrams. These modules share common standard rules for interpreting addresses and for fragmenting and assembling Internet datagrams.

1.7.3 Content Presentation Technologies

1.7.3.1 Display Technology

Display technologies can be classified into two successful groups: CRT-based and LCD-based. In a Cathode Ray Tube (CRT) based display, an electron beam hits a phosphor surface and causes it to emit light (i.e., photons ). With a Liquid Crystal Display (LCD), the display is composed of a matrix of tiny crystals each capable of emitting light (i.e., photons), when faced with an electric voltage. Plasma display technology is yet another advanced method. Since the cost of achieving an HDTV resolution with a CRT-based display is much higher than with an LCD-based or Plasma-based display, most HDTVs are not CRT-based. Recent LCD-based technologies prove to achieve HDTV resolution more effectively than plasma display.

1.7.3.2 Video Encoders and Decoders

Video encoders are components of an emission system that take video in various formats and produce a sequence of packets. Video decoders are receiver components capable of taking, as input, a sequence of packets, and producing, as output, graphic information in a format that can be readily rendered on a TV display. MPEG-based encoders and decoders perform their function while making the assumption that the sequence of packets complies with the rules laid out in the MPEG specifications.

1.7.3.3 Application Execution Environments

An application execution environment is a collection of hardware and software modules capable of identifying and extracting TV-program- related software code and data from a collection of transports, processing it, and executing it to generate a graphic user interface that can be directly rendered onto the TV display. Typically, an application execution environment includes interfaces to, and may contain as components, MPEG decoders, IP stack modules, a file system, a Web browser, a Java Virtual Machine (JVM), multimedia players, and graphics libraries. On detection of an iTV software application within an iTV transport, the execution environment is responsible for performing all steps, culminating with the launch of the application.