Globally Executable MHP
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A few years ago, the DVB project started the development of a Java-based application platform (a set of APIs), called MHP, intended to support software applications running on digital television platforms. Such applications could include Electronic Program Guides (EPG's), interactivity, Video on Demand (VOD), email through your television, etc. The MHP specification defines the download of MHP applications ("xlets") over transmission networks based on other DVB specifications (i.e. over-the-air or terrestrial networks using DVB-T, satellite networks using DVB-S, cable networks using DVB-C). As other specification bodies such as CableLabs and the Blu-ray Disc Association chose to base their own DTV software standards on MHP it became necessary to define a subset of MHP which removes the transmission-related elements of the MHP specification but retains the application API's, thus allowing broad content compatibility across a range of delivery platforms. This "subset" specification is known by DVB as Globally Executable MHP (GEM) and by the ITU as "Recommendation ITU-T J.202". GEM is not intended to be directly implemented, but rather forms the basis for broader specifications targeting a particular network infrastructure (i.e. US cable) or class of device (i.e. Blu-ray Disc players).
At the time of writing, the following platforms are defined, which base on/extend GEM:
- the Multimedia Home Platform (MHP), the open, multi-platform middleware specification developed by the DVB project,
- the OpenCable Application Platform (OCAP), which is an ITV middleware software layer for US cable,
- the Advanced Common Application Platform (ACAP) from North America’s ATSC,
- the ARIB B.23 specification from Japan's ARIB,
- BD-J the Java-platform for the Blu-ray disc, and
- GINGA-J specification from Brazil's GINGA.
As all these platforms are based on the common GEM-core, it is possible to write Java applications that will run interoperably on all these systems.
