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NBC Moves to Flexible Digital Distribution

With the pace toward total digital broadcasting quickening and vast enhancements to the TV experience on the near horizon, television giant NBC is taking a major step toward the future. The network recently installed its new Digital Skypath distribution system, hinging on a small but powerful Miranda router, in 182 affiliates across the country.

The Digital Skypath system is an evolutionary change for NBC as it replaces the analog Skypath system in use since 1983. "The former system was reaching the end of its life," says Larry Thaler, NBC’s director of distribution projects. "It was difficult to maintain because stuff was old, parts were hard to find." Most of all, "it didn’t support changes. Going into the future, we want a system that can support future business needs."

The new system gives NBC more options for transmitting its programming to affiliates. "One special feature is that it can create a custom feed for an affiliate," says Thaler. "The idea is that, depending on where you are in the country, you might need one feed or another. Some affiliates might take the feeds in a different order than others nearby." By supplying a "rack of equipment that sits at each affiliate, they’re able to switch between the feeds in a frame accurate manner as determined by scheduling systems."

Each affiliate’s rack has five receivers from Alteia, Evertz digital-to-analog converters, Intel PC servers running software from Andrew Corp., and a regular PC station for viewing scheduling. The package, integrated and installed by Live Wire Network Systems, hinged on an important element: a reliable router that switches feeds.


During development, NBC tested several routers with the following criteria: the router needed an 8 x 8 serial digital switch, a small chassis, a low price, and, most importantly, high reliability. Montreal-based Miranda fit those qualifications with its SDI 8 x 8 serial digital router from the company’s Network series.

"As part of the system, the router switches between different incoming satellite sources among the four satellite receivers at each location," says Pietro Censi, the Miranda product manager. "It serves multiple purposes such as network distribution, backup, and is ready to send stuff to affiliates later. With the router, the network can switch to a new satellite and wait for the lock up in the receivers."

"Our router is small, inconspicuous, and can sit unattended reliably," says Michel Proulx, the company’s vice president of product development. "That’s its big advantage, and it’s only 1.6 inches deep and 1 RU high. It uses a redundant power supply, but also has an alarm scheme, so if the router does fail, it can send a signal back to NBC in New York so the operators can do something about it. NBC also wanted it to be able to use simple protocol, which NBC wrote."

The Network series of routers is a success for Miranda, which offers them in 16 x 2 to 128 x 2 sizes and in 8 x 8, 16 x 16, 32 x 32 and 64 x 64 matrices. The control panels also come in a range of sizes and options. The company has sold 200-300 units of various sizes, many to Midwestern stations looking to move to HD, because the router comes in video and audio formats for analog, digital, DVI/ASB and HD options.

"It used to be that buying an HD router was complex and expensive. Miranda made it simpler," says Proulx. "The beauty of the Network series is that the router is demystified and was simplified to a compact package without complexity. Now stations are doing what they need to do to become HD, but not building huge, expensive HD systems. They will expand when they need to. They’re building small HD islands with a Network router that is simple to use, works like a plug-and-play tool and has nothing to configure."


The Digital Skypath system now allows multichannel broadcasting and feeds and remote control from the New York headquarters of NBC to its affiliates. The network can send multiple signals over a satellite, but the router and the affiliate selects only the feed it wants.

The process starts upstream at the affiliate clearance system. An affiliate calls the department to subscribe to a channel, and they are placed in that feed. The system sends info to Genesis, NBC’s central switching system, which creates the feeds and passes the info to the Andrew control software. The software alerts the stations getting the feed, and then takes the info and transmits it through a command channel through a Tandberg encoding system, which is in New York with a backup in Burbank.

The transmitter sends the signal over satellite, which is received by the affiliate receivers and processed by the Andrew software at their end. The software processes the events in realtime, and tells the Miranda switcher which feed to pick.

"The switcher is also cleaned up," says Thaler. "Even the best SDI feeds don’t synchronize clock rates perfectly, so the D-to-A units correct inconsistencies downstream. From there the stations put the signal through to the master control and then to the antenna or cable."


Besides the switch to digital, the main benefits are the multichannel feed selection, automated communication and remote control from NBC headquarters. "Now we can regionalize programming, including promotions," says Thaler. "The affiliates can receive the network schedule, which is beamed from New York. The schedule describes what programming will be broadcast at what time," and the affiliate can pick its feed.

Thanks to the remote control capability, "If NBC changes the satellite feed, the network can automatically change the feed route without calling the affiliate, so you can reconfigure the distribution straight from New York," says Censi.

The Digital Skypath system and its component parts reflect a wave of changes that has already arrived. Digital equipment improves quality and is more flexible toward changes down the road. Increased automation and remote control reduces communication time and staffing requirements. As to the pieces of the system, the simplification of the Miranda router, the standardized total-system integration of the affiliates’ new technical packages and the omnipresence of control software point toward a steady transition to easy customization and control that will result in smoother operations for broadcasters and better choices for consumers.