Skip to main content

In 1953, children could interact with the “Winky Dink and You” program by drawing on a piece of clear plastic affixed to the TV screen. Kids would be asked to draw items on the screen that would help their hero, Winky, during his adventures. For many, it is considered the first interactive TV show. Interactive TV has progressed significantly since then. In the early '70s, interactive services such as Teletext used the VBI of an analog TV signal to transmit auxiliary data during a regular broadcast. Today, new DTV services offer viewers VOD or instant access to the scores of their favorite teams, all by using the TV remote control. This month, we review some of the existing interactive TV services and examine how current ATSC standards will support interactive services in the home or on the road.

Defining interactive TV

There are multiple levels of interactive TV. At the lowest level, viewers interact with the TV by using a remote control to change the volume or channel. At a medium level of interactivity, users can actually select the desired program to watch, independent of a fixed broadcast schedule, and can control how the program is being viewed. For example, DVR functionality allows users to rewind, pause or fast-forward, on demand. In addition, Internet applications (or widgets) may overlay on top of standard TV programming and allow users to access user-defined data (such as game scores) in parallel with regular programming. All of these are local interactivity functions in that users' feedback directly affects only the behavior of the local device. At the highest level of interactivity, users (audiences) truly interact with a program and can affect how the show continues. For example, in a game show, the audience can vote in real time and help (or trick) contestants with multiple-choice questions. In that case, the interactivity operates at a system or network level.

For our discussion, we define interactive TV as any TV with a back channel. This back channel can be a dedicated uplink channel in a wired distribution system (e.g., cable or IPTV) or a separate connection to a service provider via a telephone modem or broadband connection. Figure 1 shows an example of such a system. A content provider broadcasts a TV program through any of the available broadcast media: satellite, cable, OTA or IPTV. Users receive the program either directly to their TV or through an STB. The TV or the STB is also connected to the user's home network via a wired or wireless connection. By connecting their TV receiver to the Internet via the home network, users can interact with the TV program.

Current interactive TV services

Cable and IPTV services can implement a return channel without a separate broadband connection. Some cable operators combine traditional TV programming with a variety of Internet-based features, including access to VOD, local weather and sports results. While these services are usually implemented by means of a common set of standards that allow for harmonized services and interoperability, the extent of full interactivity is usually in the ordering of VOD content.

Cable operators are also moving toward tru2way, a Java-based software platform that allows content providers to integrate a variety of new features, including interactive guides, services and VOD. Tru2way defines two types of applications: bound and unbound. Bound applications are tied to a specific channel and are delivered as part of the channel's video stream. Unbound applications allow users to interact with multiple channels and set-top applications.

Satellite operators also provide interactivity to subscribers, but a telco or broadband connection is needed. On-screen widgets that allow users instant access to a variety of Internet-based services, such as local weather, scores and image collections, are now emerging, and customized mixes allow users to view multiple sports and news programs on one screen. Also, on-demand programming can be downloaded using a home network and broadband (Internet) connection. Other interactive TV services allow users to customize how to view scores and statistics from their favorite teams. Similarly, users of the latest Internet-connected TV or Blu-ray player models can access a variety of Internet-based services, including VOD, regardless of how they receive their main TV broadcasts.

Broadcast now supports interactivity

Because of the one-way nature of broadcast, a return channel to provide full interactivity must depend on a separate, out-of-band mechanism. Two ATSC standards form the basis for how interactivity can be integrated with broadcast services: ATSC A/96 Interaction Channel Protocols and A/101 Advanced Common Application Platform (ACAP). In the ATSC A/96 specification, ATSC provides guidelines and specifications for interactive services using an ATSC broadcast. A/96 uses a five-layer reference model that includes a data-link layer, a network layer, a transport layer and an application protocol layer. In addition, network layer-related protocols are all standards-based, using TCP/IP and UDP. At the application level, A/96 uses standard HTTP 1.1 protocols. The A/96 specification does not define the physical and data-link layers.

The ACAP standard was developed as a harmonization effort between the ATSC DTV Application Software Environment (DASE) and CableLabs' Open Cable Application Platform specifications. The standard gives content providers, broadcasters, cable and satellite operators, and consumer electronics manufacturers the technical details necessary to develop interoperable services and products by defining a set of standard APIs.

Mobile DTV is built around interactivity

The ATSC A/153 Mobile DTV standard enables local TV stations to deliver live TV broadcasts to a variety of emerging ATSC-capable mobile devices. Part 3 of A/153 defines the system service multiplex and transport subsystem characteristics, which include the definition of an optional “interaction (return) channel” for interactive TV services. Mobile DTV is agnostic to the type of return channel, which could be a local Wi-Fi network or other wireless service. Although optional, this interaction channel must conform to the ATSC A/96 specification discussed earlier. Because the primary objective of the ATSC Mobile standard is to define the delivery of video and audio services, a specific method or middleware for handling applications is not currently described. The A/153 standard does, however, provide a framework for the delivery of auxiliary (graphical) components, based on the Open Mobile Alliance Rich Media Environment (OMA-RME) specification, written specifically for mobile devices.

In its report on mobile TV use cases, the Open Mobile Video Coalition (OMVC) envisions a variety of interactive TV features, including: interactive polling, interactive overlays, chat sessions and E-commerce.

As mobile devices become more common, interactive TV services will migrate from the home TV to mobile platforms, with a seamless integration of broadcasting and Internet applications.

Aldo Cugnini is a consultant in the digital television industry.

Send questions and comments to: