DVB standards consist of more than 50 technical specifications, technical reports and guidelines making up a diverse and multifaceted family of specifications and guidelines. Broadcasters (terrestrial, cable and satellite) are also not the only intended user, as the DVB standards address all the layers of the well-known OSI stack. The standards are of interest to network operators, including mobile phone and wireless terminal network operators, professional equipment vendors, consumer electronics manufacturers, software developers, content providers and many others.
Because DVB has taken more than 10 years to build this imposing and polyvalent architecture, it can be a challenge to identify which DVB standards are required and which are recommended reading. For the purposes of this article, let us say we are a user of a DVB system, not an end user or consumer, nor solely focused on creating video or interactive content. Authoring DVB-compliant interactive content is another story!
Where to start?
It is not always necessary to become a DVB member, but it can be very valuable, depending on your organization's core business. While the presence of future users and early adopters in drafting the specs was critical, the current activities of DVB are mainly so-called “last 20 percent” work items — refining existing specifications and addressing gaps, new niche solutions, and emerging delivery modes and media.
DVB standards reside at the European Telecommunications Standards Institute (ETSI), at www.etsi.org, where they can be downloaded for free upon subscription. Each key standard is denoted by a short code, and ETSI maintains a handy table giving a complete list of these reference codes, titles and brief descriptions of each document.
One of the most useful places to start reading the family of DVB specifications is the “DVB Cookbook,” which is easily the most readable document in the pile. It is maintained by DVB as a “bluebook” (A020) and by ETSI as a “Technical Report” (TR 101 200).
The “DVB Cookbook” is authored by the leader of DVB's Technical Module, professor Ulrich Reimers. It is a beginner's guide and goes through the basics of DVB systems by layer — baseband processing, transmission, conditional access and interactive services. DVB also has worked on clarifying its extended family of standards into groups, using colored graphics. (See Figure 1.)
DVB is first and foremost a solution to the needs of broadcasters, organizations that operate or hire networks to distribute signals containing video and audio. The physical layer, by a number of common television delivery media, is critical to DVB and served as an area of primary focus when the project was created.
DVB-S, DVB-C and DVB-T are each small families of specifications in their own right and were developed in that order to provide a physical layer for satellite (based on QPSK modulation), cable (QAM) and terrestrial (Coded OFDM), respectively.
In addition, the DVB-MS and DVB-MC standards specify framing, channel coding and modulation for microwave multipoint distribution services above and below 10GHz, respectively. DVB-CS is next chronologically, with a solution for satellite master antenna television (SMATV).
A new development is DVB-S2, a family of specifications for a second-generation satellite system that makes use of advanced modulation and coding techniques. It can be used in broadcasting, interactive services, newsgathering and other complex broadband operations.
Furthermore, mobile TV is supported with the DVB-H family of specifications. This area is interesting to broadcasters who may be interested in going mobile, but it is fascinating to mobile phone manufacturers and network operators who wish to receive return-channel business. DVB-H receivers face common problems with respect to battery life and power consumption, and coexisting with telephony and PDA functionality in little chips and expensive memory. There is still much work going on in this area of DVB work, and there are already several DVB-H services on the air and terminals on the market.
Mobile TV is also addressed by the DVB-RCT (Return Channel Terrestrial) specifications, which fit in-to the next category — interactive networking.
DVB always envisioned an interactive future, where the established delivery media for television would be complemented in offering interactivity via a variety of other networks. One of its first standards was a set of network independent protocols for interactive services. The fundamental concept this entails is having heterogeneous interactive loops, return traffic over a different network.
Here DVB-RCT stands out too, designed to use the same frequency at lower power for return-channel traffic. The full suite includes return channels for the three major delivery media — satellite, cable and terrestrial — and for each of the most common telephony systems — ISDN, PSTN, DECT, GSM, GPRS and UMTS. The most widely used of these is the Interaction Channel for Satellite Distribution Systems, or DVB-RCS, which is the largest family of documents, for the same reason.
DVB's Multimedia Home Platform standard is the first international standard for interactive TV. Perhaps equal in sheer weight of printed PDF to the rest of DVB's specifications, it is a family of specifications using Java and other technologies for interactive content-based services, enhanced television, interactive television and gaming.
Because the MHP is vastly different in nature to the other specifications DVB routinely works on, it has its own Web site (www.mhp.org), where the components of this family of software specifications can be more fully explained. The MHP standards also include the required functionalities useful in personal video recorder operations.
Baseband processing: video, audio and data
DVB is designed to deliver an MPEG transport stream, audio video and ancillary data to the home. DVB did not reinvent a compression system for video; rather, it chose MPEG-2. It has a set of guideline documents recommending MPEG-2 levels and profiles for HDTV and SDTV, as well as recommendations for advanced audiovisual content. This set of references and recommendations of existing ISO/IEC (MPEG) and ITU standards is grouped under the appellation DVB-MPEG.
Alongside the more obvious compressed video and audio, today's commercial operations will routinely process streams of synchronous inline data or metadata, links to asynchronous data sources, subtitles, program information, graphics, text, data or objects. In most DVB operations, several subtitle sets, as well as several soundtracks, are sent with movies.
Using program-specific information fields in this transport stream, service navigation information also is transmitted alongside the video in a set of tables, widely known as DVB Service Information (DVB-SI).
Most DVB-SI these days will contain content-specific information for a variety of standard EPG functions, basic metadata. For interactive or rich services, the ancillary data content is delivered via the various options in the DVB Data Broadcasting specification, DVB-DATA, which features the use of data and object carousels and multi-protocol encapsulation.
To support the trend toward advanced functionality such as home personal video recorders, which offer local storage for asynchronous consumption, DVB has produced a set of guidelines (DVB-TVA) for the use of TV Anytime content management and metadata signalling in DVB operations.
In the multiplexing area, DVB also has standards for conveying ITU-R Teletext, VBI Data and system software updates.
Satellite and cable delivery-based DVB operations are usually protected by one or more of a variety of available conditional-access systems (CAS). DVB has provided a package of standards in this area, from the DVB Common Scrambling Algorithm (DVB-CSA), to the widely used DVB Simulcrypt approach (DVB-SIM), which allows different CA systems to coexist on one service.
Tools and interfaces
One of the most important reasons for the quality, stability and success of DVB-based technology in the marketplace is that DVB paid close attention to developing a full set of professional tools and interfaces, and DVB-M for Measurement represents a large family of guidelines for measurement of DVB systems.
Professional interfaces defined by DVB include interfaces to PDH and SDH networks, ATM signal handling, Home Access and Home Local Networking (HAN and HLN), In Home Digital Network Signalling (IHDN), and Integrated Receiver Decoder Interfaces (IRDI).
These days, it is all online. There are three recommended paths available to the pilgrim into this labyrinth of acronyms:
Subscribe to ETSI at www.etsi.org, and download and read the standards.
Depending on the level of commercial intensity of your interest, contact a specialized digital television broadcasting consultancy.
Martin Jacklin is a technology writer and principal consultant at Broadcast Projects (www.broadcastprojects.com).