QNX on the Airwaves:
A. L. Digital's Satellite-Based "Digital Jukebox" for MC Europe

Paul Leroux, QNX Software Systems Ltd.

Backed by industry giants Sony, Time Warner International, and General Instrument, MC Europe offers the ultimate in consumer choice - 60 channels of CD-quality music.

When was the last time you picked up a radio station that played non-stop music, with absolutely no talk and no commercials? Or that broadcast everything in CD-quality sound? Or that actually let you choose the kind of music you wanted to hear?

Traditional radio stations had better watch out. Because that's exactly the kind of service offered by Music Choice Europe (MC Europe), an industry newcomer that offers cable subscribers 60 channels of continuous, CD-quality music - everything from opera through hard rock to easy listening.

MC Europe is arguably the world's most technologically demanding radio station. All 60 channels must play 24 hours a day, 365 days a year, without fail. To achieve both the high data rates and the high degree of fault tolerance that make this possible, the design and programming team behind the project chose QNX.

Playing to a Different Audience

MC Europe opened its doors in 1993 as a sister company to American-based Digital Cable Radio (DCR). DCR had been delivering music via the American cable network since 1987 and already operated an analog playout center based in Long Island, New York.

It would have been simple enough for MC Europe to pipe these existing channels across to a European satellite. Instead, they chose to develop an entirely new system, based on the latest digital technologies, and geared directly to the European market.

Nic Hopewell-Smith, MC Europe's Director of Operations, cites two reasons for the decision. "First of all, the coming of digital-satellite TV made us think that increasing our investment in analog satellite technology after 1995 wouldn't be in our best interests. Also, the American and European markets differ greatly, even in classical music. The composers, orchestras, and recordings that are popular in North America bear little comparison to those that enjoy prestige and popularity in Europe. In fact, you're as likely to find Scott Joplin or the Boston Pops Orchestra on a US classical channel as you are Mozart or Bach."

Making the Grade

The search was on for an entirely new system that could deliver sixty channels of digital audio for direct output to satellite. With no off-the-shelf solutions available, and the April 1995 launch date looming ever closer, MC Europe turned to A. L. Digital to design and program the equipment for the playout center. By this time it was September 1994, and several other companies had already tendered for the contract. However, their proposals had all failed to make the grade. Why? Because of a single major problem inherent with the design of such a system - the lack of bandwidth.

The Net Effect

On the surface, the design spec for the MC Europe system is simple: maintain up to one hundred audio channels, all simultaneously playing stereo digital audio, and control them entirely from a computer-based playlist. Also, design the system so that it runs non-stop 365 days a year, with human intervention limited to choosing the recordings and entering them on the playout database.

On closer inspection, however, achieving a constant data rate that's high enough to keep all those channels playing simultaneously becomes a major problem. QNX networking to the rescue! To achieve the bandwidth the system needed, A. L. Digital's programming team, headed by directors Ben and Adam Laurie, took advantage of QNX's ability to run multiple networks simultaneously.

"We chose QNX as the main OS for several reasons," says Ben Laurie. "First of all, it's a multitasking operating system, much like Unix, which we know and are comfortable with. Second, it's designed for realtime applications and has a respectable track record so we felt confident that we could get the continuity and reliability we needed. And third, its excellent built-in networking provides automatic load balancing across multiple network connections. Simply invoke it and you're on your way!"

Multiple Networks

With the software programming in full swing, Dominic Hawken, A. L. Digital's third director, tracked down the playout hardware:

• 22 SCSI-based jukeboxes, each containing 500 CD-ROMs and controlled by its own PC
• 60 Playout PCs (one for each channel), each containing a Digigram professional sound card

A. L. Digital connected all these machines using two main networks - one for the audio data and one for the control information used to operate the system (see diagram).

To connect to the data network, each playout PC uses one networking card. Each jukebox PC, on the other hand, uses two networking cards for data - at any one time, each jukebox is feeding up to four different audio tracks into the system! Every PC, whether jukebox or playout, also contains a single networking card to connect to the control network, which runs TCP/IP.

Non-stop Play

Making the system work is an orchestrated effort. First, music programmers in MC Europe's head office choose the recordings to be played. Next, they download the playlists via an ISDN link to one of the radio station's four SCO Unix servers, which run the system's SQL database. Then, dedicated QNX PCs at the playout center copy the selected audio tracks from CDs - these could be commercial CDs or pre-release versions - and store the tracks on bar-coded CD-ROMs ready for playout. To do this, the PCs run CD-GRAB, a utility A. L. Digital developed that digitally reads and verifies the CD via the data bus.

Next, the jukeboxes play the tracks, according to the playlists provided by the SQL servers. The QNX-based PC attached to each jukebox then routes the audio data across the QNX network to a high-speed crossbar switch, which, in turn, forwards the data to the appropriate playout PC. This happens in the background, while the playout PC is playing its current track.

Doesn't Miss a Beat Thanks to QNX, A. L. Digital didn't have to take any special precautions to ensure that the music plays uninterrupted. Because the playout program runs at a slightly higher priority than everything else, it always carries on in real time - even when other applications, such as network file copies, are launched in the background. The system never misses a beat.

Built-in Fault Tolerance Each playout PC caches up 12 hours of audio tracks on a large local hard disk. So if any part of the network fails, the engineers have plenty of time to fix the problem. And in the unlikely event that the problem can't be fixed within 12 hours, the playout PC simply starts to play the stored tracks in random order.

On most networks, you can't afford to lose sight of another section. If you do, your machine may hang or slow down while it goes off in search of the missing section. Not so with QNX. One of A. L. Digital's favorite demonstrations at the playout center is to go up to the live network rack - which is about eight feet high and crammed with network switches, hubs, and patch panels - and cut the power to it. Once the assembled visitors get over their heart attacks, they notice that the music is still coming out!

Remote Possibilities

Signals from each playout PC are encoded in Dolby AC-1 format and multiplexed for modulation onto MC Europe's satellite carrier. The satellite broadcasts the output to the major cable operators across Europe, who then redistribute the service among their subscribers. The final signal emerges from a set-top box connected to the subscriber's stereo system.

The set-top comes equipped with a remote control that not only lets the listener select channels, but also displays the title of the current song, the name of the artist, and the CD catalog number. The remote can even display text messages that announce upcoming special events for that channel.

Off the Shelf and on Schedule

At A. L. Digital, the philosophy is to use as much off-the-shelf hardware and software as possible, and to put the "smarts" in their own software to work around any problems. This is much cheaper than trying to build customized hardware, and the solutions tend to last longer and work better as the hardware is upgraded.

With its broad PC hardware support, QNX helped A. L. Digital take the off-the-shelf approach for MC Europe. Not only that, but QNX's modular architecture - which provides the freedom to change the runtime environment without having to repeatedly recompile the kernel and reboot - helped A. L. Digital deliver the solution on time.

QNX has lived up to its expectations as a solid OS, capable of performing under stressful mission-critical conditions. As a result, MC Europe's multichannel audio-on-demand is now a reality, and pulling in new subscribers every day.

Based in West London, A. L. Digital started off specializing in digital audio and video, but has since grown to encompass Internet services, teleconferencing, and a variety of other multimedia applications. Current Internet projects include "Virtual UK," which is a 3-D map of the UK being created in conjunction with Silicon Graphics and the Ordnance Survey. A. L. Digital also works with promoters worldwide to provide audio and video links between simultaneous parties.

A.L. Digital is a client of Anglia Technology, QSSL's distributor in the U.K. To reach Anglia, phone (+44) 160-378-9432 or send email to sales@anglia.demon.co.uk.