From Digital Television to Internet? A general technical overview of the- DVB- Multimedia Home Platform Specifications Vita Hinze-Hoare Abstract • System Core This paper provides a general technical The MHP is based around a Java virtual machine overview of the Multimedia Home Platform specification from Sun Microsystems to provide (MHP) specifications. MHP is a generic generic application program interface. interface between digital applications and user machines, whether they happen to be set top • MHP Profiles boxes, digital TV sets or Multimedia Pc’s. MHP This is a specification to provide a consistent set of extends the DVB open standards. Addressed features and functions. Enhanced broadcast profile are MHP architecture, System core, and MHP concerns one-way services. Interactive broadcast Profiles. profile supports the interactive services (two- way). The Internet access profile provides a gateway to Keywords: Digital Video Broadcasting, the World Wide Web. Interactive Television, MHP. 2. MHP Overview 1. Introduction MHP is produced by the Digital Video Broadcasting Multimedia Home Platform (MHP) extends Project (DVB) a European based Consortium and existing Digital Video Broadcasting (DVB) the standards (about 1400 pages long) are standards and defines a generic interface published by the European Telecommunications between interactive digital applications and a 2 Standards Institute (ETSI). range of terminals such as set top boxes, integrated digital TV sets and multimedia PC’s. DVB-MHP adopts the Java programming language and has created the DVB-Java version for broadcast application. Existing application formats can be “The Multimedia Home Platform attempts to 3 supported using optional plug – in decoders. adapt existing Internet and Web standards to digital Television. The aim is to provide 2.1. What will MHP be used for? interactive digital content that can be viewed on 1 The MHP specification envisages three modes of set top boxes and multimedia PC’s.” use The following areas are addressed: • Enhanced Broadcasting Profile (One way services) • Interactive Broadcasting Profile (two-way • MHP Overview services) This addresses how the MHP will be used what • Internet Access profile (Internet Services) it will carry and the set-top box. This will lead to the availability of such services as: • Electronic Program Guides (EPG’s) • MHP Architecture • Super Teletext The three-layer architecture of resources, • Video Synchronized content system software and applications will be • E-commerce reviewed. • Control of Access to TV content 1 2.2. How will MHP be used? passed to the on screen display. The data streams are examined for system information, teletext or MHP will transport its data through a broadcast MHP data object, and then routed via device drivers stream, which will provide the bulk of the to the hardware/software modules for interpretation content using broadcast channel protocols. and execution. These are defined in DVB standards (EN 301 192 1.2.1) and are transmitted in the same way 2.4. What will MHP carry? as conventional TV. Static formats will allow the use of basic images The Interaction Channel will use the Internet such as JPEG, Gif etc., as well as simple text, Protocol Transmission (IP), which requires a MPEG 1 Audio and MPEG 2 Video. Streaming dial-up, wireless or cable TV connection. It is formats involve MPEG Audio, MPEG Video and intended that this can in future also be used for Subtitles. There is one built in font, which is sans purely Internet based service so the Internet is serif and called Tiresias available in four sizes. fully accessible through the television. Downloadable fonts are also available. 2.3. MHP-compliant Set Top Box (STB) MHP will allow the use of Hypertext or Super The MHP places additional requirements upon Teletext referred to as DVB-Html, which is in reality the standard STB. Figure 14 below illustrates XHTML. Cascading Style sheets are supported, as the main hardware components of a typical is a Java script based language called ECMA script. digital TV STB together with the additional The document object model DOM level 2 is included components (shaded in blue) needed to for the content and structure of documents. support MHP functionality Cookies are supported, and security is available Figure 1 MHP Compliant STB4 The Radio Frequency (RF) Input within a sandbox, which limits (from satellite dish/aerial) is demodulated into access to system resources. an MPEG-2 stream. This is spliced into its video, audio, subtitle, and data streams, and 2.5. MHP Services passed on to the CPU and Operating system. The various types of MHP content presented The data stream (usually image files) has its together are called a service. Services contain own dedicated rendering engine and is directly 2 Audio, Video, Data and stored material. These can be presented simultaneously. API (Application Programming Interface) Application Application Application Application MHP presents these on three planes: Background, Video and Graphics as shown in 5 figure 2 here . System Software Application Manager Resources Figure 4: Three layer architecture 3.1.MHP resources These include Mpeg processing, I/O devices, CPU, Memory, Graphic systems etc. The resources are provided to the MHP transparently. The application Applications are provided with regions of the should be able to access all the local resources as Graphics plane to place video and graphics. though they were part of a single entity. Video is placed on the Video Plane and still 8 images on the Background Plane. Different The following table shows typical hardware applications can operate in different regions of requirements of MHP profiles. the screen in such a way that Video can be Platform Processor RAM FLASH/ROM displayed on one part of the screen with text Basic STB 30 MHz+ 1-2MB 1-2 MB appearing in a different region of the screen. MHP 8—130 MHz+ 8-16 MB 4 MB Enhanced broadcast 3. MHP Architecture profile The architecture is in three layers, and at its MHP 80-130 MHz+ 8-16 MB 8 MB Interactive basic level MHP is set in context as shown in broadcast 6 figure 3 below profile MHP Internet 150-200 MHz+ 16-32 MB 16 MB Access Profile The MHP receives viewer input via keypad controls. Output communication is presented via a screen and loudspeakers. Data streams 3.2.System Software are accessible to the MHP, which can write the This includes the real-time Operating System, Java data to storage (sink or store). The MHP also virtual machine and device drivers. Applications are may have access to remote entities. not allowed to address the resources directly. The System software is a middle layer, isolating the application from the Hardware. The purpose of this is to provide portability of the Application so that it can be used with any resources. This enables the available resources to provide an abstract view of the platform to the applications and includes the Application manager. 3.2.1 Application Manager (Navigator) The Application Manager runs the life cycle of all MHP compliant applications based on the application signaling information that is embedded in the MPEG-2 transport stream received from the DVB The diagram in figure 4 below shows the 9 software architecture with the various layers.7 broadcaster. 3.3 Applications 3 Interactive services are implemented by the Applications. These include 4.1 Java Virtual Machine (JVM) • Electronic Program Guides With the view of possible future convergence of • Information services broadcasting and the Internet Java emerged. It was • Play along Games originally designed for networked environments, has • E-Commerce built in support for Internet protocols, and many • Secure transactions security features to protect platforms from hostile or • Educational Applications damaging applications. Furthermore security is aided by the fact that Java does not permit any direct memory access. The source code for Java 4. MHP System Core applications is compiled to produce Java byte code, MHP is based around a platform known as which can be interpreted by the Java Virtual DVB- J which includes a Java virtual machine machine. Java was attractive to MHP developers specified by Sun Microsystems. Software because it too does not favour one manufacturer's Packages provide Application program operating system technology over another. Interfaces (API's) and MHP gains access to the Moreover most competing technologies already platform only through the API's. used or opted for Java for future technological developments. DVB therefore took the decision to Applications use the API to access the actual adopt Java for the MHP and developed a version resources of the receiver including databases, called DVB-J that would be suitable for interactive streamed media decoders, static content TV applications. decoders and communications. These resources are functional entities of the receiver To sum up, Java has been adopted as the and may be finally mapped onto the hardware programming language for the MHP for four main of the receiver. reasons: Figure 5 indicates a functional diagram of the enhanced broadcast profile.10,11 4 i) It was designed for a networked 2 or accessed over Internet Protocol client/server environment with build in support for connection. Most MHP compliant receivers include TCP/IP. writeable non-volatile storage allowing Xlets to be dynamically upgraded, replaced, or augmented from ii) It does not favour one a remote location.13 Tools for conditional access microprocessor over another nor one (CA), including the DVB common scrambling Operating System over another. algorithm for the encryption of transport streams like pay per view programs are available. iii). Already competitively and widely developed, which means that 5. MHP Profiles interactive TV can benefit from the MHP provides a consistent set of features in three tools and expertise developed in areas. other industries.12 5.1 Enhanced broadcasting one way services. iv) Java has a number of built in This combines digital broadcast of audio/video security features.