It's third down with one yard to go in a tight championship football game, which a cable subscriber is watching intently. The home-team quarterback prepares to receive the snap from center when, unexpectedly, an emergency-alert message crawls across the screen: There's a tornado watch in a county one-hour's drive from the subscriber's home.
Unfortunately, the message takes up enough space on the screen to block the subscriber's view of a successful forward pass.
This hypothetical example of the lack of targeted emergency-alert messages illustrates a sore spot that has plagued cable engineers. But a new initiative spurred by the Society of Cable Telecommunications Engineers (SCTE) should address that problem.
The SCTE's Digital Video Subcommittee has asked interested parties to respond to its call for information on emergency-alert issues by Sept. 15.
The sometimes irritating delivery of alert messages has become more problematic since the development of large digital headends, which often consolidate smaller analog headends.
In some systems, service areas for these large or master headends may be 100 or more miles away. Often, digital headends are located in states adjacent to the areas they serve.
Because these new facilities may be out of range of the VHF radio links and other local-transmission methods that deliver emergency information, alerts are often broadcast to areas larger than those actually affected.
Alert messages are typically carried with Program System and Information Protocol (PSIP) information as an in-channel or out-of-band data signal, depending on a specific system's channel allocation.
The Federal Communications Commission revised its rules regarding emergency-alert systems (EASs) in 1994, and placed stiff requirements on operators. Cable systems with 10,000 or more subscribers were required to broadcast national-alert messages starting Dec. 31, 1998, while systems with less than 10,000 subscribers were required to install the needed equipment to receive and broadcast the bulletins by Oct. 1, 2002. Participation in local and state emergency alerts varies from franchise to franchise.
The requirements have forced cable operators to obtain EAS equipment, including an EAS encoder/decoder, a minimum of two radio receivers, a character-generator system, and a multichannel audio/visual (A/V) switching arrangement or A/V radio frequency comb generator-all of which take up a large equipment rack.
Wendell Woody, executive director of broadband technology for Sprint North Supply, an EAS distributor, said the gear can run between $5,000 and $80,000-a huge potential burden on smaller operators.
The local alerts that a cable operator must broadcast can vary from weather warnings and watches to chemical spills or other disasters, depending on franchise agreements and the operator's discretion, said SCTE Emergency Alert System subcommittee chairman Steve Johnson, who is director of engineering and technology for Time Warner Cable.
Some franchises also require local overrides that allow officials to make emergency announcements, said Arthur Leisey, applications engineer for Trilithic Inc., another EAS systems supplier.
The list of government "event codes" runs the gamut from hurricane warnings, flash-flood watches and natural-gas leaks to prison escapes.
Given the industry-wide move toward larger digital headends, Johnson's committee is looking to establish a standardized method to target alert messages to the pertinent audience.
Two approaches are under consideration, according to Johnson: filtering messages at the digital set-top box level, or filtering alerts at the headend or hub.
In theory, set-top filters would recognize and respond only to messages sent to boxes in a certain geographic area and could target specific areas more precisely. EAS messages issued by the National Weather Service, for example, include Federal Information Processing Standard (FIPS) location codes, which indicate which areas, down to the county level and subdivisions of a county, are affected by a particular alert.
But set-top filtering would mean extra activity within a digital box, taking up valuable processing power. Also, set-tops would need to include the FIPS code information and the ability to discard irrelevant alerts.
An easier approach would be filtering at the hub level, Johnson said. That method involves sending less data into the network, but may sacrifice some targeting accuracy.
Also, Scientific-Atlanta Inc. and Motorola Broadband Communications Sector headends implement the alerts differently.
According to Woody, a former SCTE president, the Motorola/General Instrument system typically "force tunes" the set-top to an analog channel, such as 3 or 9, when an alert is received. It then returns to the channel a subscriber was watching before the alert.
The S-A system, said Leisey, conforms to the SCTE Digital Video Subcommittee (DVS) 168 specification, and allows a crawl message, with audio, to be displayed on the channel that's tuned in at the time the EAS message is received. Leisey said the Motorola DCT-5000 box would conform to the DVS specification.
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