- Interactive television standards
The concept of
interactive televisionis not new. Teletextwas introduced in the analogue televisionin the 80’s, leading to a limited interaction with our televisionset 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, 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 televisionwith 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 televisiondecoders we have at home, that see to receive and decode the digital signal in order to show it by the analogue televisionset. This device lets the users accede to the contents the digital televisionnet 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 softwarelayer on which the applications, broadcasted together with the audiovisual signals, run. This intermediary softwarelayer is called Middleware. There are different softwareclassified 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
MediaHighwayand The Open TV, but it must be taken into account that there are many more private standards.
This standard, defined by Canal Plus Technologies, represents the widest range of solutions in the market so that the
softwarein the STBs interprets and executes interactive applications, broadcast softwarefrom 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-5or HTMLand supports the specifications DVB-MHP, OCAP, DAVICor ATSCadding, at the same time, other own and new specifications.
Open TV Core
Is the most important product from Open TV, a
middlewarefor digital television(DTV) widely extended. The Open TV Core softwaretechnology contains a hardwareabstraction layer (to let the hardwarebe independent), TV libraries, a selection of execution environments for the applications, and support for Personal Video Recorders(PVRs), in order to create a DTTenvironment 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, ethernetor 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 HTMLbrowser, an Adobe Flash presentation environment and a Java Virtual Machine in compliance with the MHPstandard. 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
Let us define the standards according to its chronologic order of appearance in the market:
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 as HTMLdid 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.
This standard was created little later that 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 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
Once defined these profiles, we can speak about
There exist two versions that cover the mentioned profiles:
MHP1.0 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.
MHP1.1 that covers the three profiles. Nowadays we can't find any commercial receivers compatible with that version though there are a few compatible protocols.
The American company
CableLabscollaborated with DVBfor the creation of a new opened standard, which it led to the acceptance of the specification of the standard MHPas base for this standard, the OCAP ( OpenCable Application Platform), in January, 2002. With MHPin its center OCAP provides a common especificaión for the middlewarelayer for the systems of cable in the United States. Since in the United States DVBstandards are not used, OCAP is based on those parts that are not DVBspecific, replacing the rest of DVBspecific ones such as DVBIF API. Originally, OCAP was based on the 1.0.0 version of the specification MHP.
DVBpresented 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 MHPas 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. Itis 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:
*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.
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