Bridging the DTV gap

The business complexities of figuring out what portions of the over-the-air DTV signal will be carried by cable operators promise to be interesting. But, with today's cable multiplexers unable to transcode data transport packets so that PSIP and other information can be passed to the viewer, many discussions over what should be carried are moot.

Triveni Digital is looking to remove that technical hurdle. Its ATSC Cable StreamBridge system sits alongside the multiplexer and allows it to see what is in the PSIP or other data streams, regenerate it, and place it into the program stream.

Program and System Information Protocol (PSIP) is a part of the ATSC DTV spec that allows a DTV receiver to identify program information from the station.

"Most of the multiplexers are not PSIP-aware," says Nandhu Nandhakumar, Triveni Digital vice president of engineering and chief technical officer. "When they see transport packets in the stream that are not signaled as audio or video, they just drop those bits. And PSIP has several very useful roles for tuning and navigation."

PSIP information is important to DTV. It allows the receiver to tune to the audio and video signals. It also handles parental-control information, preserves channel branding, and signals the presence of secondary audio services.

Capitol Broadcasting Vice President John Greene Jr. points up the problem facing his group's WRAL-TV Raleigh-Durham, N.C., and other broadcasters whose DTV signals are currently carried on cable. The PSIP information is carried in the over-the-air signal but not on the cable system. With a signal that offers a standard-definition 24-hour news channel, datacasting and HD signal, channel information isn't available to the viewer.

"I think the program guide, in our case, is really critical," he says. "The way we let viewers know now is by promoting the 24-hour news channel on the local analog station, and we send out e-mails. But that doesn't reach the universe."

The StreamBridge is to be used with a remultiplexing device like the Terayon CherryPicker, Cisco RateMux, BigBand Network's BMR or Harmonic's multiplexer. It is slated to be available in the third quarter at pricing that is still to be determined.

Terayon and Triveni Digital are working on a system that allows the CherryPicker and StreamBridge to exchange information via SNMP-based interface, according to Matt Gregory, Terayon senior product marketing manager, digital networks.

"Right now, the incoming programming is seen by the CherryPicker, but we drop the non-compliant PSIP data streams," he explains. With an integrated system, such streams will be sent to the StreamBridge, which will process them, and then the CherryPicker will add the stream back into the multiplex. "We will manage the video and audio services and the bit rates, they will manage the data, and we will recombine them," says Gregory.

Given the potential for contention as broadcasters and cable operators debate limits on data carriage, the new product at least makes it easier for cable operators to carry that data.

"If a broadcaster provides program-related data that the cable operator has agreed to carry through, this does the filtering transformation merging," says Triveni Digital President and CEO Mark Simpson. "It's focused on processing data embedded in an ATSC stream and ensuring that it's formatted appropriately at the headend."

Where the software sits in the headend depends on the type of multiplexers and control platform being used. Most headends have a general-purpose PC or Sun workstation used for controlling the multiplexer.

The relationship between broadcaster and cable operator in the DTV era remains to be defined. But Simpson says StreamBridge could help.

"There will be business and regulatory agreements," he says. "This product can be configured to implement any of those, whether it's a contract between the cable operator and broadcaster or the FCC mandates something."