| What is DVB? | | | | representation of ones and zeros. In an analog |
| DVB stands for Digital Video Broadcasting, and is | | | | transmission, the wave will carry a signal to |
| a technology standard allowing the broadcast of | | | | represent the picture and audio directly by |
| video, audio and indeed any type of data. | | | | varying intensities of the components that make |
| Broadcasting means that the audience can be | | | | up the picture, and by varying some central |
| unlimited, usually millions of people in one or more | | | | frequency to represent variations in audio |
| countries. Compare this to a telephone | | | | (frequency-modulation). The three DVB standards, |
| conversation whereby the number of | | | | DVB-S, DVB-C and DVB-T, specify how the ones |
| communicating parties involved is limited, usually | | | | and zeros are carried over their carrier frequency |
| two. | | | | band. |
| The most popular type of content for DVB is | | | | A frequency band for cable or digital terrestrial is |
| television, which consists of a video stream, and | | | | called a MUX (multiplex), while in case of satellites |
| an audio stream, and usually teletext data and | | | | it is called a transponder. Essentially they are the |
| EPG (Electronic Programme Guide). Anyone who | | | | same. Each MUX or transponder carries a |
| has used a DVB set-top box (STB) from a digital | | | | transport stream (TS). Each transport stream |
| TV service provider will be familiar with these | | | | carries tens of services (TV, radio, data), |
| terms. | | | | multiplexed (split in time) inside the stream. Each |
| The medium along which DVB is transmitted can | | | | satellite provider, cable provider or digital terrestrial |
| be via cable, via satellite, or via a terrestrial | | | | transmitter will typically broadcast tens of |
| transmitter (digital terrestrial). The DVB standard | | | | transponders/MUXes, since frequency bands can |
| is widely adopted in Europe, Australia, South | | | | be tuned into separately from each other (same |
| Africa, India, while most Asian, African and many | | | | concept as an analog radio). This effectively |
| South American countries use it for cable and | | | | means that there will be hundreds of services |
| satellite only. Canada, Mexico and South Korea, | | | | available in the air or on cable, thanks to the digital |
| while adopting DVB for cable and satellite | | | | revolution! |
| transmissions, have adopted the ATSC standard | | | | Signal Encryption |
| for digital terrestrial transmissions. ATSC is | | | | One cannot have an exposition on DVB without |
| another digital broadcasting standard adopted | | | | mentioning signal encryption. Producing content, |
| widely in the United States for all types of digital | | | | such as running TV stations and building and |
| broadcasts. | | | | maintaining the distribution of the signal is a |
| How does DVB work? | | | | commercial activity. If everybody was able to |
| Like any digital storage and communication | | | | receive digital television without paying, soon |
| systems, DVB uses ones and zeros to represent | | | | these companies will run out of business and |
| the content being transmitted. With the aid of | | | | there would be nothing more to watch! That is |
| error detection and correction data stored within | | | | why not all services provided would be free to all |
| the signal itself, a DVB signal is more robust to | | | | (technically called free-to-air). Most services, i.e. TV |
| noise, and hence does not suffer interference in | | | | or radio stations, would be encrypted/scrambled. |
| the same way that an analog signal does. | | | | To be able to watch encrypted services, you |
| Furthermore, its digital nature assures that the | | | | need what is called a Conditional Access Module |
| quality of the picture being transmitted does not | | | | (CAM), and a key-card compatible with your CAM. |
| deteriorate due to electromagnetic noise | | | | The key-card can be bought from your service |
| introduced from the transmitting station to the | | | | provider retail outlet. Most set-top boxes supplied |
| receiving entity (e.g. a set-top box). You receive | | | | by content service providers (CSP) as part of the |
| exactly what is being transmitted. This guarantees | | | | paid service will already have pre-installed CAMs in |
| a sharp picture that is only limited by the quality | | | | the STB. These CAMs will be compatible with the |
| of the transmission and the quality of one's | | | | key-cards used by that service provider. If you |
| television (or screen). | | | | bought your STB from some other place, you |
| There is another major advantage of digital | | | | must make sure that the CAM you have is |
| transmission: the contents are not just limited to | | | | compatible with the key-cards your CSP supplies. |
| audio and video, but data such as Internet | | | | The key-card will contain information about the |
| packets, teletext and EPG information can be | | | | type of service you purchased, hence allowing |
| broadcast together with other services. | | | | only decryption of those services for which you |
| Furthermore, one single channel (frequency band) | | | | paid. |
| can carry a number of services (e.g. TV stations), | | | | If, instead of a STB, you use a PCI/USB card, |
| unlike its predecessor, analog transmission, which | | | | there are two choices. Some PCI cards allow an |
| could only carry only one TV station per channel. | | | | extension to be attached for holding a CAM which |
| This is why a set-top box (satellite, cable or digital | | | | you can purchase separately. So in effect you |
| terrestrial) may provide hundreds of services, | | | | plug your CAM on this CAM holder which installs |
| including radio, while analog transmission (VHF or | | | | into another PCI slot inside your computer. The |
| UHF) could only supply a handful. In digital | | | | CAM will now be linked to your DVB card via a |
| broadcasting, we do not call a TV station a | | | | cable, and if you have the correct key-card |
| channel, but rather, we call it a service. A service | | | | inserted, the CAM will be able to decrypt the |
| may consist of a group of data streams, such as | | | | service for your viewing. Another choice is using a |
| video, audio, teletext, EPG and subtitle information. | | | | Software CAM. A Software CAM is a programme |
| Satellite, Cable or Digital Terrestrial? | | | | that does the work of a hardware-based CAM. |
| The media by which a DVB signal, called a | | | | However, you still need the key-card and a |
| transport stream (TS), is transmitted can be | | | | card-reader (which is much cheaper than a CAM). |
| satellite, cable, or digital terrestrial, in the same | | | | The card-reader must be able to read your type |
| way that analog transmissions could have used | | | | of card. It usually plugs into your computer either |
| any of these. Due to the nature of the different | | | | through a serial port or USB. There are different |
| media, there are slight variations in the TS when | | | | Software CAMs available, so make sure you read |
| originating from the various sources, which are | | | | their documentation first to see what you will |
| defined by three standards: DVB-S for satellite, | | | | require. |
| DVB-C for cable and DVB-T for digital terrestrial. | | | | Conclusion |
| When purchasing a set-top box or a PCI/USB | | | | This tutorial just skimmed the surface of the |
| card for your computer, you have to decide for | | | | information that is available with respect to DVB |
| which medium you need it. This is because the | | | | technology. For instance, we said nothing about |
| hardware will still consist of an analog tuner that | | | | the actual video and audio encodings used to |
| works quite differently for each of the three | | | | broadcast the various services. This would usually |
| types of media. One has to keep in mind that, like | | | | be MPEG-2, however recent high-definition (HD) |
| its analog counterpart, content has to be | | | | technologies require the use of different encoding |
| modulated, i.e. carried onto an electromagnetic | | | | types, such as H.264 and AC3 for digital surround |
| wave. You cannot send ones and zeros right into | | | | sound. |
| the air! In DVB, the wave will carry a | | | | |