- Interactive television standards
The concept of
interactive television is not new.Teletext was introduced in the analoguetelevision in the 80’s, leading to a limited interaction with ourtelevision set to obtain information about the telecast schedule, the weather, and so on. 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, asCanal+ , 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 formattelevision 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 asinteractive television .All of these can happen thanks to the Set-Top-Boxes or
Set-Top-Box (STBs), thetelevision decoders we have at home, that see to receive and decode the digital signal in order to show it by the analoguetelevision set. This device lets the users accede to the contents thedigital 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 intermediarysoftware layer on which the applications, broadcasted together with the audiovisual signals, run. This intermediarysoftware layer is calledMiddleware . There are differentsoftware classified depending on they were of public or private property. Next, we will go over that classification.Private Standards or private property
We will just mention a couple of standards in this article: the
MediaHighway and The Open TV, but it must be taken into account that there are many more private standards.Media Highway
This standard, defined by Canal Plus Technologies, represents the widest range of solutions in the market so that the
software in the STBs interprets and executes interactive applications, broadcastsoftware 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 orHTML and supports the specificationsDVB-MHP ,OCAP ,DAVIC orATSC adding, at the same time, other own and new specifications.Open TV Core
Is the most important product from Open TV, a
middleware fordigital television (DTV) widely extended. The Open TV Coresoftware technology contains ahardware abstraction layer (to let thehardware be independent), TV libraries, a selection of execution environments for the applications, and support forPersonal Video Recorders (PVRs), in order to create aDTT environment for the decoders (STBs). The TV libraries include support for rich graphics (RG) andHigh 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, aHTML browser, an Adobe Flash presentation environment and a Java Virtual Machine in compliance with theMHP standard. The ‘C’ Virtual Machine is an execution environment that allows theAPI s 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
Let us define the standards according to its chronologic order of appearance in the market:
MHEG
If we go over the history we will see that the notation “open standards” is not new. As early as 1997 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 asHTML did for documents at the proper time that is, to give a common exchange format that should be executed in every receiver.There were created several versions:
"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. Because of that, in April 1997, they create a new version, the "
MHEG-5 ", that should be a simpler picture of the first version.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.Though the MHEG-6 was not extended, it was the base of the
DAVIC 's (Digital Audio Video Council ) standard.DAVIC
This standard was created little later that the MHEG-6 in 1998. It was created adding a new series of
API s Java to MHEG's sixth version. TheAPI s 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 receiverDAVIC , theAPI s [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 one is the standard 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.Once defined these profiles, we can speak about
MHP 's versions.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 we can't find any commercial receivers compatible with that version though there are a few compatible protocols.OCAP
The American company
CableLabs collaborated withDVB for the creation of a new opened standard, which it led to the acceptance of the specification of the standardMHP as base for this standard, the OCAP (OpenCable Application Platform ), in January, 2002. WithMHP in its center OCAP provides a common especificaión for themiddleware layer for the systems of cable in the United States. Since in the United StatesDVB standards are not used, OCAP is based on those parts that are notDVB specific, replacing the rest ofDVB specific ones such asDVB IFAPI . Originally, OCAP was based on the 1.0.0 version of the specificationMHP .Later,
DVB presented the specificationGlobally Executable MHP (GEM) to facilitate the use ofMHP 's elements in other specifications. OCAP's recent versions use GEM instead ofMHP as base, but they refer to someMHP '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. Itis also based on GEM and adds some OCAP's elements that are adapted for the USA market.Interesting webs
For more information you can visit these pages:
*MHP: http://www.mhp.org/
*MHEG: http://www.mheg.org/
*Canal+ Technologies: http://www.canalplus-technologies.com/
*Open TV: http://www.opentv.comalso you can read next book:
*Steven Morris and Anthony Smith-Chaigneau, "Interactive TV Standards: A Guide to MHP, OCAP, and JavaTV". Elsevier 2005.
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