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The New European Digital Video Broadcast (DVB) Standard ------------------------------------------------------- Markus Kuhn -- 1996-07-08 This text gives a brief introduction into the technology behind the new DVB/MPEG-2 TV broadcasting system. The latest version of this text can always be found at <URL:ftp://ftp.informatik.uni-erlangen.de/ pub/multimedia/tv-crypt/dvb.txt>. Use a monospaced font to display it. Special thanks to Hanno Basse <hb@tvhm.de> for his many very valuable comments and contributions to this text, as well as to Didier Aernoudt <didier.aernoudt@ping.be> for supplying additional information. Errors in this text are of course my fault. Any comments, additions, and corrections to this brief overview are very welcome! [The market situation description of this text is at the moment at some places not very up to date and describes the situation in early 1996, but the described standards and technical details are still unchanged. Markus -- 1996-11-16] Contents -------- 1 Introduction 2 Building blocks 2.1 MPEG-2 source encoding 2.1.1 Handling 16:9 images on 4:3 screens 2.2 Modem standards 2.2.1 Satellite transmission (DVB-S) 2.2.2 Cable transmission (DVB-C) 2.2.3 Community antenna installations (DVB-CS) 2.2.4 Terrestrial transmission (DVB-T) 2.2.5 Compatibility 2.3 System information and Electronic program guide (DVB-SI) 2.4 Teletext 2.5 Subtitling 2.6 Conditional access control (pay-TV encryption) 2.6.1 Common Interface (DVB-CI) 2.6.2 SimulCrypt 3 Market overview and system introduction schedule 4 Hints for DVB receiver buyers 5 Literature and sources for more information 1 Introduction The next generation of TV signal broadcast standards is based on digital data compression and digital data transmission. This provides both higher image quality and better bandwidth utilization than classic analog color TV broadcasting standards such as PAL, NTSC, and SECAM. In January 1995, the Digital Video Broadcasting (DVB) project organized by the European Broadcasting Union (EBU) has published a set of formal standards which define the new Digital Video Broadcast system. These DVB standards are the technical basis for implementing digital TV transmission in Europe, Asia, Australia, and many other regions of the world starting in 1996. DVB seems to be the best candidate for a single global digital TV broadcasting standard. Only the U.S. plan their own terrestrial HDTV standard which is also based on MPEG-2 but they use a modem, an audio encoder, and an electronic program guide incompatible with DVB standards. Current DVB standards describe digital TV transmission over satellite and cable; modulation standards for terrestrial broadcast are under preparation. DVB standards cover the system design and the modem standards for high bandwidth video data transmission as well as several auxiliary functions like teletext, electronic program guides, and conditional access. The compression technique used by the DVB system is the ISO MPEG-2 algorithm. The following brief description of the new DVB standards originated as my notes from a talk about the topic given by C. Schaaf from German Telekom, FTZ Darmstadt, at the INTERSAT '95 exhibition in Frankfurt am Main on 1995-02-03. Later I extended it with information taken from DVB Project Office press releases and the DVB standards. I am not an expert on the subject, only an interested observer who wants to make some information about the future of digital TV available to the interested network community. 2 Building blocks The block diagram of a DVB receiver (aka "set-top box") looks roughly like this: cable or antenna | V receiver -> demodulation -> error correction -> optional access control and decryption module | V MPEG demultiplexer | +----------------------+-----------------------+ | | | V V V MPEG video decoder MPEG audio decoder data transmission interface | | | | | +---->-----+------<----+--<-- EPG/teletext <---+ | | V V RGB/S-Video/PAL/PAL+ encoder Personal Computer or Modem | V TV set/VCR/ Hifi system The first generation of DVB consumer receivers is expected to be a set top box, i.e. a small box which contains only a receiver (satellite and/or cable) and the above MPEG decoder. These receivers will have the usual RF and SCART interfaces to the antenna, cable, and TV/VCR. In addition, the receivers are expected to have also data transmission interfaces for personal computers and other multimedia systems (EIA-232-E) as well as one or several ISO 7816 chip card slots and PCMCIA type 2 connectors for the pay-TV access control module. Additional interfaces might include digital audio. Later, DVB receivers will become integral parts of TV sets and video cassette recorders. The DVB Project Office has so far published the following standards as European Telecommunication Standards Institute (ETSI) standards: DVB-S Digital broadcasting systems for television, sound and data services; Framing structure, channel coding and modulation for 11/12 GHz satellite services, ETS 300 421, December 1994. The modem standard for satellite broadcasts with various data rates, band width requirements, and error correction capabilities. DVB-C Digital broadcasting systems for television, sound and data services; Framing structure, channel coding and modulation for cable systems, ETS 300 429, December 1994. The modem standard for cable broadcasts with various data rates, levels of noise immunity, and band width requirements. DVB-CS Digital broadcasting systems for television, sound and data services; Satellite Master Antenna Television (SMATV) distribution systems, ETS 300 473, May 1995. Description of the alternative ways in which a community sat antenna installation head-end could operate. DVB-SI Digital broadcasting systems for television, sound and data services; Specification for Service Information (SI) in Digital Video Broadcasting (DVB) systems, ETS 300 468, October 1995. Electronic program guide and automatic tuning and VCR control information broadcasted in DVB data streams. DVB-TXT Digital broadcasting systems for television, sound and data services; Specification for conveying ITU-R System B Teletext in Digital Video Broadcasting (DVB) bitstreams, ETS 300 472, May 1995. MPEG-2 encapsulation for the European analog teletext data. DVB-CI Common Interface Specification for Conditional Access and other Digital Video Broadcasting Decoder Applications, European Standard prEN 50221, Draft D, 1996-04-23. PCMCIA slot that will allow to add proprietary access control and other extensions. Not yet ready. DVB-?? A Common scrambling algorithm, pay-TV access control; will probably never be available publicly. The DVB-S standard has now also been included in ITU-R recommendations. Further DVB standards for terrestrial digital broadcast (DVB-T), subtitling, MMDS, and interactive TV are under preparation. In addition, two ETSI Technical Reports (ETR) have been published that are not formal standards but form important guidelines for system implementors: ETR 154 Digital broadcasting systems for television; Implementation guidelines for the use of MPEG-2 systems; Video and audio in satellite and cable broadcasting applications, ETSI Technical Report, draft ETR 154, 1994-11. The MPEG-2 standard ISO/IEC 13818 specifies a very large number of system parameters and optional features. This text specifies many MPEG-2 minimum parameter ranges and options which every DVB receiver is supposed to support. ETR 211 Digital broadcasting systems for television; Implementation guidelines for the use of MPEG-2 systems; Guidelines on implementation and usage of service information, ETSI Technical Report, final draft ETR 211, 1996-02-12. This text provides many important details for implementing the DVB-SI standard. 2.1 MPEG-2 source encoding The DVB project has not defined its own image encoding algorithm, but has only selected a profile (subset) of the international standard ISO/IEC 13818 (commonly referred to as MPEG-2) in the ETR 154 document. MPEG-2 is an audio/video compression algorithm optimized for broadcast quality transmissions up to HDTV quality based on the discrete cosine transform and motion estimation. The DVB project selected the MPEG-2 Main Profile at Main Level (MP@ML) with a maximum data rate of 15 Mbit/s. Main Level means that up to 720x567 pixels at 25 Hz (the TV standard frequencies used in Europe) or up to 720x480 pixels at 30 Hz (the TV standard used in North America) are supported with either 4:3, 16:9, or 2.21:1 aspect ratio. Main Profile means that MPEG bidirectional B frames are supported but that no SNR or resolution scalability is used. In ETR 154, the following parameters have been selected as minimum requirements that should be supported by all DVB receivers: Video: - Frame rate of 25 Hz in film mode and field rate of 50 Hz in video camera mode. - Aspect ratio of both 4:3 and 16:9 (2.21:1 is optional). - Receivers should support pan vectors that allow to display the most relevant portion of a 16:9 image on a 4:3 display with correct aspect ratio. Support for letterboxing (i.e., resampling the image to a smaller number of lines such that the full 16:9 image is visible on a 4:3 screen with black bars at the bottom and top) is optional. - Luminance image resolutions: 720x576, 544x567, 480x576, 352x576, 352x288. Audio: - MPEG-1 single channel, MPEG-1 dual channel, MPEG-1 joint stereo, MPEG-1 stereo, MPEG-2 compatible multichannel audio. - Sampling frequency: 32 kHz, 44.1 kHz, 48 kHz. The following three are optional: 16 kHz, 22.05 kHz, 24 kHz. - Encoded audio has no emphasis, 50/15 or ITU-T J.178 de-emphasis are optional for the receiver. - bitrates for layer I audio are in the range 32 to 448 kbit/s, for layer II in the range 23 to 384 kbit/s. Using layer II is recommended. "MPEG-2 compatible multichannel audio" means: The MPEG-2 standard allows to encode a 5+1 surround sound signal (i.e., speakers in four corners and a center speaker plus a low frequency subwoofer) in a way, that allows simpler receivers with only a normal MPEG-1 stereo decoder to decode a correctly mixed normal stereo signal, while surround sound decoders can decode a full 5+1 signal from the same bitstream. For more details about the surround sound capabilities of MPEG-2 and DVB, check <URL:http://www.keymodules.philips.com/MD/mpeg/index.htm>. There exists even a compatible extension to MPEG-2 that allows to encode 7+1 signals as they are used in good cinemas, which can be decoded as either 7+1, 5+1, dolby surround, or stereo signals in the DVB receiver. [By the way: Originally, the U.S. digital TV standard "Grand Alliance" planned to use the proprietary Dolby AC-3 encoding instead of standard MPEG audio in their U.S. broadcasting system, which is not DVB compatible but also based on MPEG-2. The results of their listening tests showed that AC-3 provided superior quality to MPEG audio coding. However, recently they discovered that the MPEG audio demo system used in the "Grand Alliance" tests contained an implementation bug and new listening tests showed now that MPEG audio and AC-3 produce fully comparable signal quality. Let's hope that the U.S. abandons AC-3 quickly and therefore will not introduce their own incompatible audio encoding system. This would make MPEG *the* single world-wide audio and video encoding standard.] The MPEG-2 standard also specifies higher levels (for high definition TV) and higher profiles (which allow for instance to broadcast different image quality layers with different error correction overhead such that the image quality can degrade smoothly under bad receiving conditions). As only an MPEG subset is used today, the DVB system can easily be upgraded to these advanced functions later in an upwards compatible way when the market is ready for HDTV. DVB systems are required to skip data structures which they not not understand in order to allow easy future backwards compatible extensions of the DVB standards. The bit rate utilized for a video program can be selected freely depending on the quality requirements. Typical bit rates are: 2 Mbit/s: approx. VHS quality, suitable for simple signals like comics 4-6 Mbit/s: approx. PAL quality (e.g., for talk shows) 8-9 Mbit/s: better than D2MAC and PAL+, comparable to studio production quality (e.g., for cinema films and sport events) >15 Mbit/s: Various levels of HDTV quality For the MPEG-2 audio encoding options, the DVB project has selected the MPEG-1 layer II algorithm from ISO/IEC 13818-2 which is based on the MUSICAM sub-band coding system. A typical audio bit rate is 192 kbit/s for a high quality stereo signal. MPEG allows arbitrary many audio channels (for various languages or surround sound) to accompany the video image. The MPEG-2 standard also defines a multiplexing system (ISO/IEC 13818-1), which allows to combine many video, audio, and data streams into one single data stream. In DVB, this multiplexing technique is used to allow to put many different programs into for example one 38 Mbit/s data stream, which the DVB data transmission standards allow to transfer per satellite transponder or per 8 MHz cable TV channel. This 38 Mbit/s bandwidth can be used to transmit simultaneously for example either: Video: each program 2 - 9 Mbit/s -> 18 - 4 video services Audio: each program 192 kbit/s -> 190 radio stations Data: each channel 64 kbit/s -> 590 data services each channel 2.4 kbit/s -> 15800 data services MPEG-2 multiplexing uses a packet length of 188 bytes, each packet consists of a 1 byte header and 187 bytes data content. SES expects that typically between six and eight programs will be placed on one Astra transponder, which leaves between 4.75 and 6.34 Mbit/s per TV program. I would not expect much better image quality than what you get with analog PAL from these bitrates. With four programs per transponder (9.5 Mbit/s), MPEG-2 image quality should be excellent. 2.1.1 Handling 16:9 images on 4:3 screens The first cinema films were filmed in 4:3 aspect ration (the "academy format"). Early TV standards adopted this format in order to stay compatible with cinema. However, movie producers went on to the wider 16:9 format in order to to allow more impressive scenes (and perhaps also to simply make cinema different from TV ;-). More recently, films are often produced in the even wider 2.21:1 cinemascope format. If a 16:9 or cinemascope image has to be displayed on a 4:3 screen, there are two commonly used techniques to adapt the aspect ration of the image: pan&scan and letterboxing. Pan&scan means, that the broadcaster or movie producer has decided for every part of the film, which 4:3=12:9 window of the full 16:9 image is most interesting for the viewer. The remaining 25% image area will be cut away on 4:3 screens: +-----XXXXXXXXXXXXXXXXX--+ | X X | | X X | X = visible 4:3 screen | X X | - = full movie image | X X | | X X | | X X | +-----XXXXXXXXXXXXXXXXX--+ Pan & Scan Method The second alternative is known as letterboxing. The size of the image is reduced by 25% such that the full 16:9 image fits exactly onto the 4:3 screen with black bars on the top and bottom border of the image. XXXXXXXXXXXXXXXXX X X X---------------X X = visible 4:3 screen X X - = full movie image X X X---------------X X X XXXXXXXXXXXXXXXXX Letterbox Method Special 3/4 vertical filtering hardware is necessary which removes every fourth line of the 16:9 image in a smooth way, in order to provide high quality 16:9->4:3 letterboxing. There are also compromise solutions possible: XXXXXXXXXXXXXXXXX +--X---------------X+ | X X| X = visible 4:3 screen | X X| - = full movie image | X X| | X X| +--X---------------X+ XXXXXXXXXXXXXXXXX Combination of Pan&Scan and Letterboxing The average viewer seems to prefer pan&scan and considers letterboxing as a waste of valuable screen area. The cinema freak however knows that pan & scan throws away 25% of the movie and that the 4:3 format is not what the director and camera operator had in mind when they produced the movie. Therefore, the expert viewer usually prefers letterboxing. It has so far been impossible for broadcasters to make both normal viewers and cinema freaks happy at the same time. This changes with digital TV! The movie is broadcasted digitally in whatever format of the original film had. Pan&scan vectors are provided in the MPEG-2 data stream. They the tell the MPEG-2 video decoder which would be a suitable place for the 4:3 pan/scan window on the wide movie image. Whether pan&scan or letterboxing or some compromise format is used to display the movie on a 4:3 screen is now decided in the DVB receiver and not any more at the broadcaster. This allows every viewer individually to switch between pan&scan, letterboxing, or some compromise format. Pan&scan or letterboxing is most important on 4:3 screens which are very different from 16:9 and 2.21:1 cinema formats. If a 2.21:1 cinemascope movie is broadcasted, even if you have a 16:9 screen, also some (much less serious) form of pan&scan or letterboxing has to be applied in order to display the 2.21:1 format on your 16:9 screen. 2.2 Modem standards As there have been no suitable international standards for digital satellite, cable, and terrestrial modem transmission available, the DVB project had to define new standards here. The various transmission mediums have very different characteristics, therefore it is not possible to use only one single modulation standard for all of them. 2.2.1 Satellite transmission (DVB-S) Channel properties of satellite transmission are: - relative low signal/noise ratio - large frequency bandwidth available - amplifier tubes in the satellites are operated in a very non-linear mode for maximum power efficiency The selected satellite modulation system is a 2 bit/symbol QPSK (quaternary phase shift keying) modulation. This modulation system is defined in the DVB-S standard ETS 300421. Some characteristics are (this is only for interested modem experts): - scrambling applied for spectral formation - outer FEC: Reed Solomon Forward Error Correction RS(204, 188, T=8) - convolutional interleaving (Forney) - inner FEC: convolutional Code - 35% half-Nyquist filtering - flexible symbol rate The DVB-S standard has a number of encoding parameters that allow to choose an appropriate set of transmission parameters for the characteristics of a specific satellite transponder. The reception parameters that the DVB-S receiver must be able to handle are - carrier frequency (GHz) - polarization (horizontal, vertical) - convolutional error correction code (1/2, 2/3, 3/4, 5/6, or 7/8) - symbol rate (Mbaud) The variable symbol rate allows the broadcaster to adjust the modem exactly to the bandwidth available by the transponder. The selected symbol rate will typically be the -3 dB bandwidth of the transponder divided by 1.28. ETS 300 421 does not restrict the symbol rate in any way. The five different forward error correction (FEC) codes allow to vary the amount of redundant information that is added to the MPEG-2 transport data stream. This way, the modem can be adapted for different signal/noise ratios. For example, it might be possible that a broadcaster who usually uses the 5/6 code goes back to the more robust 2/3 code during an important football match when many people might start to complain about reception problems caused by heavy rain in their area. 3/4 means for example that 3 out of 4 bits carry MPEG data, the remaining 25% of the bits are inserted for error correction. The available different error correction codes allow to adopt the modem transmission to the hydrometrological conditions in the reception area. The broadcaster can select with the error correction code how many expected minutes of image loss per year caused by heavy rain are acceptable for the average viewer in the reception area. The DVB-S system is optimized for single carrier per transponder Time Devision Multiplex (TDM), however it is able to be used for multi-carrier Frequency Division Multiplex (FDM) type applications. There will be applications for satellite news gathering (SNG) where a 8 MHz channel is used in Single Channel Per Carrier (SCPC) technology. SCPC means, there is only one program (with one video and its related audio streams) transmitted on that carrier. This allows several DVB-S uplink sites to share one single transponder by using different carrier frequencies (FDM). The contrary to this is MCPC (Multiple channels per carrier), which is used for normal broadcasts. All these methods are compatible to (or at least can be performed compatible to) the DVB-S standard. 2.2.2 Cable transmission (DVB-C) Typical cable channel properties are: - good signal/noise ratio - small usable frequency spectrum - echos and non-linear distortion The selected cable modulation system is a 64-QAM (quadrature amplitude modulation system with 64 symbols), which has the following characteristics: - high spectral efficiency - low required bandwidth (8 MHz) - requires adaptive pre-emphasis This modulation system DVB-C is defined in ETS 300429 and some of the technical details are: - scrambling applied for spectral formation - outer FEC: Reed Solomon FEC RS(204, 188, T=8) - convolutional interleaving - 15% half-Nyquist filtering - optional 16-QAM and 32-QAM, extensible to 128-QAM or 256 QAM. - flexible symbol rate RS forward error correction and interleaving are identical to DVB-S which reduces the implementation effort in systems that convert DVB-S into DVB-C. The reception parameters that the DVB-S receiver must be able to handle are - carrier frequency (GHz) - symbol rate (Mbaud) - QAM type (64, 32, or 16 bit/symbol) 2.2.3 Community antenna installations (DVB-CS) Several options are available for systems where one single satellite dish supplies a large number of receivers: System A: The head-end demodulates DVB-S signal and remodulates it into DVB-C, so that normal DVB-C cable receivers can be connected to the distribution network. This system is called SMATV-DTM (digital transmodulation). Because of the high price for the additional modems, this method is more interesting for very large cable TV installations. Whether the head-end implements outer error correction or simply passes data through without decoding and reencoding Reed-Solomon and convolutional interleaving is optional (this does not cause compatibility differences anyway). System B: The cheapest solution for short cables: head-end converts received signal only down to intermediate frequency above 950 MHz without touching the QPSK modulation (SMATV-IF). A slightly more expensive solution for longer cables and more receivers (SMATV-S): the head-end converts the received signal down to the intermediate frequency and then again down to a part of the VHF/UHF band like the extended S-band (230-470 MHz) without touching the QPSK modulation. 2.2.4 Terrestrial transmission (DVB-T) The DVB-T standard is not yet finished. The technical proposal currently under discussion is: - OFDM (Orthogonal Frequency Devision Multiplex) - 8192 carrier frequencies, each modulated using a QAM with between 4 and 64 Symbols - 8 MHz bandwidth - outer FEC: Reed Solomon FEC RS(204, 188, T=8) - outer convolutional interleaving - inner FEC: Convolutional Code (1/2, ..., 7/8) - inner interleaving With 8192 separate carrier frequencies, the typical elimination of some frequencies due to multi-way path reflections in terrestrial transmission becomes tolerable. On terrestrial DVB there has been a very lengthy discussion, since it is most challenging from the engineer's point of view. Now they have decided to have 8192 carriers with downward compatibility to 2K carriers. The 8K carriers make the system feasible for single frequency networks (SFN), but the 2K may be used, when SFN are not required. One of the main hurdles for terrestrial DVB is the cost of such a system. It is very expensive, because it is designed for mobile reception. Meanwhile it becomes clear, that mobile reception is not too necessary for video services. In addition there is already a standard for terrestrial digital transmissions - DAB. With DAB (Digital Audio Broadcasting) you can broadcast audio, data and even MPEG-1 video. This was recently shown at the Institute for broadcasting technology in Munich. Thus, the very complicated DVB-T standard remains with a question mark. 2.2.5 Compatibility All three transmission systems are designed for maximal compatibility, which means that they can use common circuit blocks (e.g., the Reed Solomon decoder and interleaver) if a single receiver supports several transmission mediums. Compatibility also means that transmodulation is made easy when the bitrates are selected carefully. As a practical example, let's have a look at the parameters used in the Astra 1E satellite and the cable systems fed by it: Many DVB-S satellite transponders (e.g., Astra 1E/1F/1G, DFS, Eutelsat Hotbird) have a bandwidth of 33 MHz, which allows with QPSK a symbol rate of 33 MHz / 1.2 = 27.5 Mbaud. With 2 bit/symbol, this results in 55 Mbit/s and after the convolutional 3/4 FEC decoder has removed 25% of the bits for inner error correction, 41.25 Mbit/s remain. This bit stream is sent to the second error correction algorithm (Reed-Solomon), which transforms 204 bytes into 188 corrected bytes and the final error corrected data rate is therefore 38.015 Mbit/s for the multiplexed MPEG-2 data stream. In a typical DVB-C cable system, there are 8 MHz channels, and after the 15% roll-off specified by DVB-C, a theoretical maximum symbol rate of 6.96 Mbaud is possible. For compatibility with the above DVB-S example, let's use 6.875 Mbaud with a 64-QAM, which results again in 41.25 Mbit/s including Reed Solomon redundancy. As before, after the RS-decoder, the final bit rate remaining is 38.015 Mbit/s. As both satellite and cable modem parameters can be selected to use the same final bit rate, satellite signals can easily be converted into a cable signal by pure transmodulation. A satellite->cable converter does not have to touch any Reed-Solomon codes or any MPEG-2 multiplex information. This allows cheap large community antenna installations (see DVB-CS). There are also Astra transponders with 26 MHz bandwidth and Eutelsat plans for the W24 satellites 72 MHz bandwidth transponders. For these satellites, other DVB-S symbol rates than 27.5 Mbaud will have to be applied in order to utilize the full bandwidth of the respective transponder. The required worst case bit error probability for all modulation and forward error correction (FEC) systems is 1e-11, i.e. there must not be more than one wrong bit in the 38 Mbit/s MPEG data stream every 45 minutes, in other words not more than one wrong bit in a 8 Mbit/s TV program every 3.5 hours. 2.3 System information and electronic program guide (DVB-SI) DVB defines a Service Information standard (ETS 300468), which uses an MPEG data channel in order to transmit technical parameters of the transmission as well as electronic program guide (EPG) information for the user. Technical parameters transmitted include the broadcast parameters (frequency, polarization, FEC, symbol rate, QAM type, MPEG multiplex identifier, etc.) and identification of the services available in the multiplexed channels. This allows the receiver software to configure itself completely automatically, even if broadcast parameters change (e.g., because of a satellite transponder rearrangement). The satellite receiver must only be configured once to find the first transponder. After a few minutes, the receiver will know the parameters of all channels on all other transponders. The Electronic Program Guide information transmitted includes: a) Distribution network id (e.g. "SES Astra" or "German Telekom") b) Channel id (e.g. "Sky Movies Gold" or "ZDF") c) Program (e.g. "James Bond: Goldfinger") d) Program type (e.g. "film", "news", "sports event", ...) e) Service Provider (e.g. "British Sky Broadcasting") f) Bouquet (e.g. "Sky Multichannels") g) Broadcast time (e.g. 20:15 - 22:30) h) Description text (e.g. "Classical secret service adventure, actors: ..., director: ..., etc.") All this information is not only transmitted for the current program, but also for the following program, for alternate channels and for the program of the next 2 weeks. All electronic program guide times are transmitted in Universal Time (UTC) and it is the job of the software in the receiver to translate it into the user's local time. This way, the electronic program guide times displayed all over the continent will all show the respective local time. The Electronic Program Guide also contains the information necessary to start/stop a VCR precisely with a film independent on any unscheduled delays or commercial breaks in the program, and it contains parental guidance information that allows parents to restrict their children's access to on-screen sex and violence. DVB-SI therefore also performs the functions of the VPS (Video Programming System) that was available for these purposes on analog channels in Germany and other countries since the early 1980s. 2.4 Teletext The DVB-TXT standard (ETS 300 472) defines, how EBU-Teletext, which is known for analog video services, can be transmitted within a DVB-bitstream. This has been set up, because many of the now existing analog programs will want to simulcast analog and digital signals in order to make a migration from one system to the other easier. The digital receiver is supposed to insert the teletext data into the vertical blanking interval. A connected TV-set with built-in EBU-teletext decoder can then handle this like the usual teletext. DVB-TXT is not the specification of a new next generation teletext service. 2.5 Subtitling They say it's a standard for subtitling but it is very powerful and can display many things, not just subtitles. It can be used as a very high level teletext platform. 2.6 Conditional access control (pay-TV encryption) Like the earlier pay-TV system EuroCrypt and VideoCrypt, DVB access control will be separated in two parts: decryption and descrambling. Descrambling operates directly on the MPEG transport data stream or on individual channels located inside this stream. The DVB project has standardized a Common Scrambling algorithm. It is a combination of a 64-bit block cipher followed by a stream cipher algorithm. The technical details of the Common Scrambling algorithm are secret and only made available under a Non-Disclosure-Agreement for access control hardware manufacturers. The decryption is the section of the access control system that receives reception entitlement messages from the MPEG transport stream, decrypts and processes them, manages the subscription activation status of this receiver and finally forwards to the descrambling part the control word necessary to descramble the next few seconds of the program. Unfortunately, the DVB consortium has not been able to standardize a common encryption algorithm. One of the primary reason was the fear of pay-TV piracy (e.g., cloned smart cards with the copied decryption keys and algorithms). Two alternative solutions have been discussed that would still allow to use one single receiver in order to receive channels from different pay-TV providers: The Common Interface and SimulCrypt. 2.6.1 Common Interface (DVB-CI) The Common Interface is a slot for one or even several type 1 or type 2 PCMCIA cards (now called PC-Card). The receiver can send the full MPEG-2 transport data stream as it comes out of the demodulator and error correction units through the card plugged into the Common Interface, before it will be processed by the MPEG demultiplexer in the DVB receiver. If several CI cards are present, the MPEG transport data stream will be passed sequentially through all these cards. A CI card can request control over decoder functions. It can talk to ISO 7816 smartcard slots which the receiver might also provide in order to keep parts of the decryption algorithm there, it can generate on-screen messages and receive remote control commands, and it can talk to a telephone modem which might be present in the receiver in order to handle online pay-per-view and near-video-on-demand functions. A CI card will typically contain a hardware implementation of the Common Scrambling algorithm as well as a security processor with decryption software. Parts of the decryption software might also be implemented in an ISO 7816 smartcard that can be exchanged at much lower cost in case of successful piracy hacks against the decryption system (just as this has happened several times already with VideoCrypt and EuroCrypt). After power-up, a Common Interface card acts like a PCMCIA memory card. Several memory locations act as data transmission registers that allow communication with the processor on the CI card. This way, a CI card can also be plugged into a normal laptop PCMCIA slot and some limited card functions could be accessed this way. When the descrambler in the CI card is activated, the most-significant-byte of both the address and data bus turn into 8-bit parallel input and output busses for the MPEG transport data stream. Other pins will then be used as separate byte clock and packet clock lines for both directions. Although the Common Interface was primarily intended to allow plug-in decryption modules, it is not limited to that application. May be, this interface will in the future be used to connect other extension modules to the DVB receiver, like Internet browsers, interactive TV, PC video boards for harddisk recording, high speed PC satellite data acquisition systems, etc. 2.6.2 SimulCrypt The problem of the non-existence of a common decryption standard can be solved by plugging CI cards for all required decryption standards into the receiver. The existing standard for the Common Scrambling algorithm allows however also another approach: A broadcaster might provide the decryption data for its channel in the formats necessary for various decryption systems in the data stream. This way, various different encryption system would decrypt the entitlement messages with their proprietary methods, however finally they would all find the same control word which they send to the same Common Scrambling algorithm. The SimulCrypt idea is not new: BSkyB has been using it for years on those channels like MTV on Astra that can be received both by VideoCrypt 1 and VideoCrypt 2 receivers simultaneously. SimulCrypt is a nice way of avoiding the need to have several CI cards plugged into one receiver. It is therefore cheaper and more user friendly. However, SimulCrypt works only if the broadcaster from which you bought your decryption system cooperates with the pay-TV broadcaster from which you want to see a channel. For full broadcaster independence, you will still need the Common Interface in your decoder. 3 Market overview and system introduction schedule German Telekom has installed in >150 German CATV networks hardware for three digital 8 MHz channels which will reach 80% of all German cable users (11.5 million households). Astra 1E, the first satellite of the European Astra series designed completely for DVB-S compatible digital broadcast has been launched in late 1995 and is currently already broadcasting several DVB channels. DVB-S consumer receiving equipment for Astra 1E and other DVB-S satellites will start to be available in 1996, when the Astra 1E test phase ends. The second DVB-S satellite Astra 1F has also been launched recently. Eutelsat on 13 degrees east is also broadcasting a number of DVB-S channels. In the far future, the German Telekom CATV system might perhaps use all channels for digital transmission, which gives a total bit rate of >2 Gbit/s. This would allow to transmit for instance 237 highest image quality TV programs (8 Mbit/s each) or 950 medium quality TV signals (2 Mbit/s each) or a combination of various quality levels somewhere between. Although DVB is a European system, it was used for the first time outside Europe (Australia and South Africa). Within Europe, we have in some countries very clear constellations and in others very unclear ones. In the UK there's ol' Rupert Murdoch and BSkyB and nobody else who might launch digital satellite services. Since Sky has a lot of analog transponder capacity, they don't seem to hurry towards DVB. But, there is a strong momentum towards DVB-T with 2K carriers (other broadcasters than Sky). In France, the major player is of course Canal+. They plan to start a regular service spring 1996. The largest TV-market in Europe, Germany, lies down paralyzed by the silly fight of two very big companies: Kirch and Bertelsmann/MMBG. Both of them want to introduce their own decoders, which are, in spite of the existence of standards, NOT compatible. Thus, the market is splitted in two and a potential customer has to decide between two boxes. With one box you can watch the Kirch package, with the other box Bertelsmann's. If you want both packages - buy two boxes. The advantage of Kirch is his immense stock on movies and licenses. Bertelsmann is now the third largest media company in the world. Recently, they have joined forces with Rupert the Australian, mainly to overcome the problem with the lack of movie licenses. So there is a fight between two systems just like VHS versus Beta for home video. My personal estimation is, that services will not start before the end of this summer. Another big fish is Nethold, planning services in Italy, the Benelux countries and Scandinavia. 4 Hints for DVB receiver buyers So what reception equipment is available? Up to now, there's only expensive professional equipment available. Most of these devices have still some software bugs and other teething troubles. Some of them only work with a certain kind of encoder so in some cases you can tell, what encoder they have on the transmitter side. It's all still in a stadium of experimenting. Consumer equipment (set top boxes) will become available together with the launch of services. The closest estimation one can make: this year. Here are a few things on which you might want to pay attention to when you decide to buy a DVB receiver. Keep in mind that especially the first generation will have a number of limitations like - not all modem parameters are supported (which might limit you to reception from a specific satellite type or broadcaster) - the DVB-CI common interface is not yet supported (which might limit you to a single pay-TV provider) - the subtitling standard is not yet supported Especially the common interface (CI) is a very important feature in case you are interested in pay-TV. I highly recommend not to buy a DVB receiver that is not equipped with a CI slot (which will cause around around 80 DEM additional manufacturing costs). As there will be no common single DVB encryption standard, by buying a DVB receiver with only a built-in fixed decryption module, you will be bound to the offerings of one single pay-TV provider. With the CI slot, you will be able to easily exchange the complete encryption module yourself and your DVB receiver will not get obsolete very quickly. Unfortunately, the DVB-CI standard has not yet been finished, so it will take quite some time until the first DVB receivers with common interface become available. When the DVB-CI standard is ready, ask specifically for the common interface slot when you buy your receiver! Better DVB receivers might even provide several common interface slots such that you don't have to switch PCMCIA modules when you switch channels. Good DVB receivers will display the current bit error rate of the signal, which will help you to position the dish very accurately in order to avoid image dropouts caused by bad weather. An optional audio signal indicating the signal strength is also very helpful when you are sitting on the roof aligning your dish onto the satellite. Good DVB receivers should be able to display the MPEG-2 parameters (bitrate, resolution, etc.) of the current channel in some technical information submenu so that you can get an objective information about which image quality the broadcaster has decided to be good enough for you (especially important if you are technically interested and pay for the quality you get!). MPEG-2 theoretically allows to bring full studio quality to the home, but the actual image quality depends on the bitrate assigned to a channel which depends on the number of channels per transponder. When managers decide which image quality is sufficient to their viewers, the result might be something around 4 Mbit/s which is not necessarily any better than current analog PAL, while a critical eye would prefer twice the data rate for a really good image quality. Although a DVB receiver will be able to configure itself completely automatically, it should still offer you to easily rearrange the allocation of the channels on the channel selection menus and the remote control channel numbers. In a good DVB receiver you can easily change the initial channel parameters (frequency, polarization, FEC, symbol rate, etc.), so that you can get the electronic program guide information not only from one fixed transponder on one satellite, but can use other future DVB satellite systems as they emerge. You should also be able to enter the reception parameters manually in order to be able to have a look at those channels which are not mentioned in any electronic program guide. Good DVB receivers will not only provide pan&scan display of 16:9 and 2.21:1 movies on your old 4:3 TV set, but also allow you to switch to a letterboxing presentation or to select a combination of pan&scan and letterboxing. As MPEG-2 can optionally encode not only stereo but also 5+1 surround sound, you might want to check whether the DVB receiver you plan to buy is supporting 5+1 surround sound decoding. If you own a video cassette recorder with VPS support or a TV set with VPS parental guidance password lock, then you should check, whether the DVB receiver you are interested in can automatically reproduce the VPS signal from the Electronic Program Guide information, so that your VPS video recorder still works. If you want to use a community antenna installation, make sure your DVB receiver supports the DVB-CS SMATV alternative that your community antenna is using (see the section on DVB-CS): For SMATV-DTM, you will need a DVB-C cable receiver, for SMATV-IF or SMATV-S you'll need a DVB-S receiver that has an IF or S-band receiver, respectively. Good DVB receivers will allow over-the-air updates of their microcontroller software, which is important especially for first generation devices that usually have a few software bugs and compatibility problems. 5 Literature and sources for more information The DVB-related standards and further information are available from: DVB Project Office European Broadcasting Union Case postale 67 - 17A Ancienne Route CH-1218 Grand Saconnex (Geneva) Switzerland phone: +41 22 717 27 19 fax: +41 22 717 27 27 e-mail: dvb@pax.eunet.ch Web: <URL:http://www.ebu.ch/dvb_home.html> International Organization for Standardization (ISO) Case Postale 56 CH-1211 Geneve 20 Switzerland phone: +41 22 749 01 11 fax: +41 22 733 34 30 e-mail: sales@isocs.iso.ch Web: <URL:http://www.iso.ch/> European Telecommunication Standards Institute (ETSI) F-06921 Sophia Antipolis CEDEX France phone: +33 92 94 42 00 fax: +33 93 65 47 16 Web:: <URL:http://www.etsi.fr/> Quite good information about the DVB market situation and new rumors and developments can be found in the monthly German sat-TV magazine "infosat" (ISSN 0933-6907). A German book that covers in detail the modem and compression technology behind the DVB and MPEG standards is Ulrich Reimers: Digitale Fernsehtechnik -- Datenkompression und ▄bertragung fⁿr DVB, Springer-Verlag, Berlin, 1995, 291 pages, ISBN 3-540-58993-7, DEM 98,- Goetz Kluge <goetz.kluge@p54.mch2.siemens.net> mentioned that there is now a 2nd revised edition: Ulrich Reimers: DVB, 1996, ISBN 3-540-60945-8. An English translation might be available at the end of this year. An English book about DVB is HervΘ Benoit: Digital Television : MPEG-1, MPEG-2, and Principles of the DVB System, Arnold, London, 1997, ISBN 0-470-23810-4. A very good source of information on DVB for people in North America is http://www.coolstf.com/mpeg/ Copyright (C) Markus Kuhn 1996. [end]