ns and "Internet over the air" services for PCs and TVs equipped with set-top boxes (STBs).
In Franc
e, for example, Canal Plus's C:Direct residential software broadcast service transmits 500 software titles to a subscriber's STB every month. Users can select the titles they want and pay for them via a credit-card-like on-line transaction over the telephone return channel. Out of Canal Plus's 500,000 digital TV subscribers, 10,000 users in France and nearly 4000 users in Spain subscribe to C:Direct.
Several of Europe's national carriers and alternative telecommunications operators are starting to provide access
to the Internet
over asymmetric digital subscriber lines (ADSLs) and cable TV modems. This is happening in France, Germany, Switzerland, the Netherlands, and Austria.
Media companies and equipment manufacturers are also launching Web services based on analog TV broadcast signals that go beyond the traditional teletext or videotext services. For example, MediaNet's NetOnAir, Intel's Intercast, and Philips' Webcast services use the vertical blanking interval (VBI) with
its one-way 230-Kbps throughput to deliver selected "Best of the Web" content into European homes. Deutsche Telekom is working on a service delivery via the horizontal blanking interval (HBI). However, it will not be commercially available before 1999.
NetChannel, an Internet access and content provider, launched a European Internet-on-TV service in the U.K. last October. It builds on a standard TV, the telephone network, and an inexpensive STB for interactive Web access and e-mail. The company is also exploring cable TV networks in addition to the Public Switched Telephone Network (PSTN).
WebTV, a similar operation that also delivers Web services to TV and PC users via an STB, is planning its first European launch in the U.K. later this year.
The Bandwidth Problem
Digital Audio Broadcasting (DAB) is a possible broadband channel for consumers. Standardized by the European Telecommunications Standards Institute (ETSI) and the International Telecommunication Union (ITU), any combinati
on of radio programs, data services, and Web content with a throughput capacity of up to 1.8 Mbps can be transmitted over a DAB network.
Although its downstream data transmission rate isn't suitable for MPEG-2 video compression, it is a reliable medium for datacasting and may well be used to stream MPEG-1 and other video formats that require less bandwidth. Offerings from early commercial services coming up on DAB networks this year in Europe will include electronic newspapers, selected Web pages, and stock information.
Many receiver and DAB-chip manufacturers will have products ready by the middle of the year. Product designers at radio equipment manufacturer Robert Bosch Multimedia Systems see DAB as a multimedia channel to deliver video to passengers on subways, trains, and minivans with its videocasting-over-DAB application. The idea is to deliver not only interference-free audio but also crisp TV pictures to moving vehicles. Trials performed in Sweden and Germany have shown that it is possibl
e to deliver VCR-type video quality on 1.7-Mbps channels.
Hooking Consumers
Most of these services aim, at least initially, at PC users at home and in businesses, because of the PC's ability to efficiently process and display multimedia data. But the average home PC penetration rate of just 20 percent in Europe is a clear barrier to the growth of these new services.
That's why the media and computer industries are so excited about digital TV and so many electronics companies are in the STB business. Digital TV is widely seen as the first broadband path to the huge consumer market in Europe.
Digital TV satellites based on DVB may ultimately be the most promising distribution platform for multimedia services. They provide pure data-broadcast services and real-time interactive services, and may cover most of the world.
Digital direct-to-home satellite TV services are already available in Scandinavia, Germany, France, Benelux, and Italy. They offer digital bouquets from broadcaste
rs such as Telepiu, DF1, Canal Plus, BSkyB, and TPS.
Canal Plus's C:Direct was the first to offer commercial data broadcasts over a digital TV satellite to consumers last year. News Corporation's technology subsidiary, NDS, started pilots in the U.K. last summer. Beta Business TV, an offshoot of Kirch Group's Beta Digital, and Pro Sieben Digital Media are offering business-oriented data-broadcasting services in Germany. Further broadband data services delivered via digital TV this year will come from Astra, called European Satellite Multimedia (ESM), and Eutelsat.
However, especially in urban areas, data broadcasting over digital TV will not replace wireless or cable networks. Instead, it will bring broadband multicasting to closed user groups or the distribution of Web data. "As an overlay network, it adds multicasting capabilities to the Internet," says Bernhard Collin-Nocker, a researcher at the University of Salzburg's department of computer studies.
Nearly 1000 broadcasters are using DV
B satellites on five continents. DVB satellite data services use a broadcaster's extra satellite transponder space to broadcast data into the home. Users receive the data streams on their PCs via a standard 10,700-12,500-GHz satellite dish and a DVB-compliant STB or a DVB-compliant PC extension board.
Although DVB has the capacity to offer an overall throughput of up to 38 Mbps, most services available in Europe this year will use one 700-Kbps channel. To enhance bandwidth, the transponders carry a multiplex system that allows for the aggregation of multiple channels.
DVB data broadcasting lets you receive large multimedia files such as MPEG-2 video, multimedia-rich HTML pages, or large binary files. However, pure data broadcasting limits interactivity to what the service provider sends to everybody. In this case, STBs and PCs store broadcasted data locally, so you can browse, play back data, and select the files you want.
Better DVB Return Channels
Browsing the whole Web interactiv
ely, however, needs a return channel. That's why DVB satellite STBs are being equipped with modems. Users can interactively purchase a book, book a movie ticket, and browse the Web sites they want. In addition, the DVB consortium has already issued specifications for Digital European Cordless Telecommunications (DECT), Global System for Mobile Communications (GSM), and ISDN back channels. Says Martin Jaecklin of the DVB organization in Geneva, "The DVB data-broadcasting and return-channel specifications pave the way for a high-speed 'Turbo-Internet.'"
In the long term, DVB satellites will even be able to establish point-to-point connections with users' satellite dishes. The Astra consortium, for example, plans to launch later this year the Astra 1H satellite, which carries a Ka-band payload capable of communicating on the return path at 2 Mbps. Bidirectional satellite communications require a new receiver component in your satellite dish, but you don't have to replace the complete system.
However,
don't expect this functionality at your home anytime soon. The target markets will be large multinational organizations. According to an Astra spokesperson, "Fully interactive transmissions, allowing the bypass of terrestrial networks will be offered to business users in 1999."
In contrast to bidirectional satellite communications, service providers will commercially deploy asymmetric Web/satellite gateways such as AINS's Advanced Data Broadcast System (ADBS) this year. ADBS gives you full interactive Web access and supports unicast (i.e., point-to-point), multicast, and broadcast applications. The return link is usually a telephone line plus a modem to access an ISP. Eutelsat's Multimedia Platform, Italian RAI, and Com.Net say they'll offer ADBS-based services.
ADBS sits between a Web proxy server and the satellite uplink (
see the figure
). You configure your Web browser so that it directs all requests to this proxy server. The system then processes requests by loading Web p
ages from its local cache or fetching the requested pages from the Internet. Instead of sending the pages back over the telephone line, it sends data via satellite back to the PC.
ADBS supports several levels of conditional access, security, and privacy. Only authorized users may connect to the proxy, which serves users according to the scheduling strategies implemented by the system manager. Every user station has a unique hardware identification number that is used for individual addressing of stations. The current implementation can deliver data at a rate of about 8 Mbps.
A Carousel of Multimedia Data
DVB systems deliver multimedia streams, including compressed video and audio. Expressed in more technical terms, DVB's specification is based on the MPEG-2 Digital Storage Media Command and Control (DSM-CC) in combination with the DVB Service Information standard. DSM-CC is a set of ISO/IEC13818-6 protocols that are independent of the transport layer. This lets applications be delivered o
ver a multitude of broadband networks.
DSM-CC comprises four generic application-delivery mechanisms. The Data Carousel protocol periodically broadcasts data to the DVB decoders. It sends a list of available modules, so that each client can identify the appropriate software modules to download.
This mechanism doesn't require a return channel from client to server, because the decoder software receives all the relevant control information (e.g., start time and channel number) from the DVB server. Although the Data Carousel was originally intended to access multimedia libraries, it has been adapted for first-generation "Internet over the air" services on the upcoming digital TV networks. It provides an efficient way to make multimedia Web sites available to a large audience without increasing Internet traffic.
However, the Data Carousel's revolving data broadcast is not appropriate for interactive applications. DVB offers three alternatives for interactivity. All of them involve encapsulating
or wrapping data inside several headers.
The Data Piping mode transports nonsynchronized bit streams. Data Streaming supports synchronous data. The Multi-Protocol Encapsulation transport mechanism best supports various packet-switching protocols. Note that you can use any one of these protocols to transfer TCP/IP data packets. Most of the recent interactive DVB Internet trials that offer a broadband back channel via cable or ADSL modem have used Multi-Protocol Encapsulation, although some have also deployed the Data Carousel.
The flexibility of DVB broadcasting protocols is inspiring a good deal of development work in Europe and the U.S. "A lot of researchers are working on DVB-based solutions for broadband Internet access," says Collin-Nocker, who has conceived several experimental DVB design studies and product prototypes. According to Collin-Nocker, many product studies use DSM-CC to transmit IP. Some products, however, use the Packetized Elementary Stream (PES) protocol.
In contrast to D
SM-CC, PES contains timing information to synchronize different data streams and allows for selective coding of control information. PES is more efficient than DSM-CC, but not all MPEG-2 chips can reassemble PES packets. AINS's SatServer, for example, is based on PES. New DVB products from Nokia, IBM, ComAtlas, and Sat/Sagem are also expected to use this protocol.
Home Networks
The STB is the central relay station in the multimedia home envisioned by digital TV proponents. It not only receives digital TV signals from the satellite dish, it also handles e-mail communication, Web browsing, and general multimedia decoding in a couch-potato environment.
Various STB designs have emerged from vendors such as Sat/Sagem, Nokia, Sony, Pace, and Acorn during the last three years. Features vary, but all have interfaces to the PC. Sat/Sagem, for example, uses a bidirectional, asynchronous parallel interface (IEEE-1284), where others deploy RS-233 or SCSI ports.
In the near future, however, thes
e boxes will most likely have an IEEE-1394 FireWire connector. This enables several STBs and other multimedia devices to be connected to each other. The decoder would then function much as a hub for all the in-home networks and services.
But before an STB can become the multimedia platform of the home, it needs a certain level of hardware and software standardization. "Only a common STB standard will allow consumers to receive content from a wide range of service providers and broadcasters," says Graham Mills of BT.
Although today every vendor uses its own set of APIs, there are some solid candidates for a standard API. The Digital Audio/Video Council (DAVIC), for example, promotes an API based on ISO standard MHEG5 (Multimedia and Hypermedia Information Coding Expert Group) and Java, now called MHEG6. According to Philip Laven, director of the EBU technical department, "Several DVB members seem to favor the choice of an open API based on MHEG5 and Java."
Another candidate for an STB API sta
ndard is OpenTV, developed by the company of the same name, a software solution company that's owned by Myriad International Holdings, Thomson Multimedia, and Sun Microsystems. OpenTV is expected to come out with its first detailed specification of an open API soon. The company has already announced that it intends to develop STB reference designs based on Sun's MicroSparc and JavaChip processors. In either case, it's likely that the next generation of STBs will capitalize on Java's virtual machine.
Super TV
While many companies are working on standardizing separate STB designs, a lot of the functionality is moving into TV sets. With an internal storage capacity, signal processing, and MPEG-2 decoding, this integrated design is called the smart TV or super home TV.
Says Peter Bondar, senior vice president for technology and engineering at Acorn, "For the stand-alone home market, the network computer (NC) has lost its opportunity, at least in the volumes that were originally conceived. But
there are now new types of devices emerging that rely on the NC concept."
Super home TV systems have e-mail, Web browsing, picture-in-picture (PIP) functionality, videoconferencing, home automation, fax, and voice messaging.
Says Acorn's Bondar: "We expect product designs to quickly cluster around the key concepts of super home TVs."
Where to Find
Acorn
Cambridge, U.K.
Phone: +44 1223 725005
E-mail: kcoleman@acorn.com
Internet: http://www.acorn.com
Webcasting Over the Air
