PSIP: Trojan Horse, or Information Sherpa?
by Leslie Ellis // August 19 2002
Lo and behold, just two columns into the intricate hues of digital and high-definition TV, a rule on the subject emerges from the Federal Communications Commission.
It says that big screen TV sets (>= 36″) made in and after 2005 must include circuitry, interchangeably referred to as “tuner” and “receiver,” that can recognize and administer digitally-transmitted, over-the-air TV signals. By 2007, the rule continues, all new TVs need a way to receive and display the stuff that comes in digitally, from the antenna on the roof.
In the fog of digital TV lingo, the FCC’s mandated tuners tune the stuff of “digital terrestrial television” — the digitized programs you get, or will get, from broadcast stations.
As with most other entertainment media, the very process of “going digital” usually includes methods to automate related business functions. Remember the column (4/15/02 edition, “How a Film Becomes a VOD”) about “metadata,” the data that describes other data? It discussed how a digitized, compressed film gets packed along with things like its promotional materials, trailer and airing dates, before it makes its journey to become a VOD offering.
Traditionally, those materials would either go on the sticker of the hand-delivered film can, or arrive under separate cover.
Digitally, they’re all in the bit stream.
The same is true of broadcast digital signals. The extra stuff that goes with a broadcaster’s digital signal goes by an acronym: “PSIP,” as in, rhymes with “key clip,” or “be hip.” PSIP stands for “Program and System Information Protocol.” It’s a standard, built by the Advanced Television Systems Committee. (For those who care, it is the ATSC’s A65/A standard.)
In a sense, PSIP is mega-metadata — an information sherpa, hauling a ton of descriptive data, organized into lots of tables – eight, at a minimum.
One table keeps track of time. Another holds ratings information. A third tells the tuner where to look to pluck the digital channel, or channels, out of the incoming bit stream. Yet another table contains data describing the programs on those channels. A minimum of four other tables, each with three hours worth of upcoming program information, make the TV smart enough to know what’s on digital broadcast stations for the next 12 hours.
Those tables get sliced into sections, and slotted into the MPEG-2 transport stream – picture an airplane, with 188 seats, one for each byte of info. It flies the chopped-up PSIP tables to rooftop antennas, and down into digital tuners inside TVs.
Some of these tables matter to cable because they describe merchandise that may or may not be a part of carriage agreements.
Indeed, in the technical documentation that describes the PSIP standard, it is a foregone conclusion that the 19.2 Megabits per second of digital throughput, originally awarded to the broadcast industry for high definition television, will also be used to convey multiple, “standard definition” channels. Even NVOD applications are discussed.
Those standard definition channels are known in the PSIP standard as “minor channels,” as opposed to a “major channel,” which is whatever channel a particular broadcaster is on today, in analog. So if PBS is on channel 12, its extra programming goes on “12-1,” “12-2,” “12-3,” and so on. Channel 12 is the major channel. Anything after the delimiter (the dash, or the dot, or whatever is ultimately decided) is the minor channel. Both are held in a PSIP table called a “VCT,” for “Virtual Channel Table.”
If cable is the storefront, and its bandwidth the shelves, then PSIP looks sort of like a supply truck that pulls up out front to unload the thing you’ve agreed to put on a shelf – and with it, several other things that you perhaps didn’t agree to display.
Therein lies some concern: If those minor channels fall outside the bounds of a cable/broadcaster carriage agreement, can the DTV receiver tune them anyway? Probably. The fact that this kind of activity is technically capable is disturbing, to some cable strategists.
However, it probably also makes sense to consider the overall likelihood of PSIP as a Trojan horse. Broadcast TV, at least for now, is free. For broadcasters to fill the “minor channels,” they need more content. That takes resources and money. If the plan is to somehow forge a for-pay model, the logistics involved in setting up provisioning and billing systems, not to mention mitigating consumer backlash, are daunting.
Either way, expect to run into this “PSIP” term on a fairly regular basis, especially if you’re the one that will undertake operational, tactical or strategic liaisons with broadcasters and TV manufacturers.
This column originally appeared in the Broadband Week section of Multichannel News.