Interactive television standards
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Teletext was introduced in the analogue television in the 80's, leading to a limited interaction with television sets to obtain information about things like the schedule and weather. But nowadays this concept goes even far away and a new and improved way of interaction with the user has been developed. The early private broadcasters, as Canal+, were the pioneers in adopting this new form and today are preceded by their digital formats.
As a consequence of the Analogue Switchoff the Project known as Digital Terrestrial Television (DTT) was developed creating a public digital format television with more features, in competition with private broadcasters. Among this features one can found interactive menus that, as in the case of the private broadcasting, give information to the user and let them adapt the product to their own needs. This user-television interaction is today known as interactive television.
All of these can happen thanks to the Set-Top-Boxes or Set-Top-Box (STBs), the television decoders that households usually have at home, that see to receive and decode the digital signal to show it by the analogue television set. This device lets the users accede to the contents the digital television net offers. One of their many functions is running the interactive applications, being this the object of this article.
For interactivity, it is required that the STBs could be dynamically programmed and updated. For that, there are some different solutions in the market, among them, the definition of an intermediary software layer on which the applications, broadcast together with the audiovisual signals, run. This intermediary software layer is called Middleware.
Private Standards or private property
It was defined by Canal Plus Technologies, which represents the widest range of solutions in the market so that the software in the STBs interprets and executes interactive applications, broadcast software from the server for the broadcasting of applications and data via satellite, cable and terrestrial nets, moreover runs interactive applications and their execution environment. Also, includes different profiles to better respond to the broadcasters needs.
These standard runs applications written in different programming languages as Java, MHEG-5 or HTML and supports the specifications DVB-MHP, OCAP, DAVIC or ATSC adding, at the same time, other own and new specifications.
Open TV Core
The most important product from Open TV, a middleware for digital television (DTV) widely extended. The Open TV Core software technology contains a hardware abstraction layer (to let the hardware be independent), TV libraries, a selection of execution environments for the applications, and support for Personal Video Recorders (PVRs), to create a DTT environment for the decoders (STBs). The TV libraries include support for rich graphics (RG) and High Definition (HD), net communication from phone line up to broad band IP (via DSL, ethernet or fibre), management of the digital audio and video signals (DVB, as well as another standards and proprietary formats), and support to authentication and encryption by using CA/DRM systems. Open TV Core supports a number of Applications environments execution(AEE) including the 'C' Virtual Machine, a HTML browser, an Adobe Flash presentation environment and a Java Virtual Machine in compliance with the MHP standard. The 'C' Virtual Machine is an execution environment that allows the APIs of the Open TV software Developers Kit, that lets the content providers create, in O code, applications centred on TV by using the development tools from Open TV or another sellers.
Open or Public Standards
As early as 1995 the ISO (International Organisation for Standardisation), together with the Multimedia and Hypermedia Experts Group, published the MHEG standard. This gave a statement approach to the creation of multimedia applications that could work in every operative system in compliance with this standard. Conceptually, MHEG intended to do for multimedia applications the same as HTML did for documents at the proper time that is, to give a common exchange format that should be executed in every receiver.
MHEG-1: this version included support for objects containing procedure codes, that could widens the basic model of MHEG-1 adding decision making functions, as it was not possible in other way.
MHEG-3: this version defined a standard virtual machine and a byte representation code that allows its portability through hardware platforms.
These versions were unsuccessful, since they were based on concepts very complicated and the industry was not ready for the characteristics they offer. MHEG-5, the simpler version of MHEG-1, was created in April 1997.
Many of the functions that were shaping it were equal but simultaneously there were many differences between the two versions. MHEG-3 was overcome by the success of Java and in 1998 they decided to create the sixth version, MHEG-6, which was based on the fifth version adding a support for the use of Java to develop objects script, mixing the declarative force of MHEG with the procedure elements of Java. For doing this, they defined a Java application programming interface (API) for MHEG so that the code Java could manipulate MHEG objects in its mother application.
This standard was created little later than the MHEG-6 in 1998. It was created adding a new series of APIs Java to MHEG's sixth version. The APIs of the above-mentioned standard were allowing the objects Java the access to some services of information, control of services of audio content and video and the managing of the management of the resources in the receiver. Though the creation of an application was not possible pure Java for the receiver DAVIC, the APIs Java already was capable of controlling more elements of the receiver of what was possible with other standards.
DVB-MHP(The Multimedia Home Platform)
This is defined by the Digital Video Broadcasting (DVB) to offer interactive services in the DTV. It is a limited version of the virtual machine of Java, where a set of extra functionalities are added for the adjustment to the environment of the DTV. With the purpose of arranging the specification of this standard there are defined three profiles related to the capacities of the STBs:
- 1. Enhanced Broadcast Profile: interactive applications are downloaded via broadcasting. It does not incorporate backward channel in the STB.
- 2. Interactive Broadcast: incorporates bidirectional communications via backward IP channel towards the server, allowing the download of applications.
- 3. Internet Access: STB processes extreme internet contents.
There exist two versions that cover the mentioned profiles:
- MHP 1.0 that covers the first two profiles. This version is the one that the current receivers use and the majority implement the second profile. Many countries have adopted it to offer their DTV's interactive services, like Spain, Italy or Finland.
- MHP 1.1 that covers the three profiles. Nowadays it could not be found in any commercial receivers compatible with that version though there are a few compatible protocols.
The American company CableLabs collaborated with DVB for the creation of a new opened standard, which it led to the acceptance of the specification of the standard MHP as base for this standard, the OCAP (OpenCable Application Platform), in January, 2002. With MHP in its center OCAP provides a common especificaión for the middleware layer for the systems of cable in the United States. Since in the United States DVB standards are not used, OCAP is based on those parts that are not DVB specific, replacing the rest of DVB specific ones such as DVB IF API. Originally, OCAP was based on the 1.0.0 version of the specification MHP.
Later, DVB presented the specification Globally Executable MHP (GEM) to facilitate the use of MHP's elements in other specifications. OCAP's recent versions use GEM instead of MHP as base, but they refer to some MHP's elements that are not included in the especificaión GEM.
ACAP (Advanced Common Application Platform)
This platform was created by the Advanced Television Systems Committee (ATSC), as common base for all the systems of interactive TV in USA, for cable, terrestrial or satellite. It is also based on GEM and adds some OCAP's elements that are adapted for the USA market.
For more information you can visit these pages:
- MHP: https://web.archive.org/web/20060421101018/http://www.mhp.org/
- MHEG: http://www.mheg.org/
- Canal+ Technologies: http://www.canalplus-technologies.com/
- Open TV: http://www.opentv.com
also you can read next book:
- Steven Morris and Anthony Smith-Chaigneau, "Interactive TV Standards: A Guide to MHP, OCAP, and JavaTV". Elsevier 2005.