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PSIP Revisited: Getting it Right - TvTechnology

PSIP Revisited: Getting it Right

Nearly two years after the FCC mandated the use of PSIP, reports can still be heard of stations struggling to get it right.
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Nearly two years after the FCC mandated the use of PSIP, reports can still be heard of stations struggling to get it right.

Anecdotal evidence indicates that some stations do a much better job than others, and some are apparently still not doing everything required. The FCC incorporated the entire ATSC Program and System Information Protocol for Broadcast and Cable (ATSC document A/65) into its rules in February 2005. Fortunately, ATSC has developed tools that promise to make PSIP implementation easier and more accurate.

BACK TO BASICS

PSIP is a collection of data structures within every DTV broadcast that enables receivers to find the components needed to create a TV program. This information is organized into virtual channels and programs or events. The virtual channels are identified using a two-part major/minor channel number. The major channel number allows broadcasters to leverage the NTSC channel number brand for DTV.

The three core PSIP tables are:

• System Time Table

• Virtual Channel Table

• Event Information Table

These tables contain information to enable receivers to find the components needed to present a particular program at a certain time.

Each event can have TV parental advisory, or V-chip information; it must indicate the presence of each closed-caption stream, and can provide extended text messages.

There are certain must-have items and must-do rules of operation. If the PSIP elements are missing or wrong, there may be severe consequences, depending on the type of receiver-including not being able to tune your station. Table 1 summarizes the key parameters that must be set and/or checked by each station.

ATSC and Consumer Electronics Association recommended practices advise that three days (24 EITs) of program titles should be sent-with real titles-to enable a meaningful program guide to be presented to the consumer who watches more than one channel.

Several operating parameters may be automatically set by the DTV equipment, sometimes manually by the original equipment installer.

However, for some of these parameters-unless an automated control system is in place-a change in one piece of equipment or the configuration of channels in a multicast can result in nonconformance, or worse, the inability of a receiver to tune the channel. See Table 2.

A checklist of key PSIP items is at http://www.nab.org/scitech/PSIP_checklist.pdf.

To facilitate automated generation and update of PSIP data, the ATSC developed A/76, "Programming and Metadata Communication Protocol." This standard makes it possible to integrate the various information sources needed to compile the key PSIP tables.

PMCP is designed to permit broadcasters, professional equipment manufacturers and program service providers to interconnect and transfer data among systems that eventually must be communicated to the PSIP generator. These systems include:

• traffic

• program management

• listing services

• automation

• MPEG encoder

The overall goal is to ensure proper PSIP implementation while requiring minimum manual intervention by the broadcaster.

PMCP is based on a protocol utilizing XML (eXtensible markup language) message documents. The heart of the standard is an XML schema that defines the message structure, the elements allowed, their relationships and attributes. XML is widely recognized as flexible and usable for various system architectures.

Equally important, it can be deployed without extensive development costs on the part of equipment vendors and/or service providers. XML is a W3C standard that allows structuring of information in a text document that is both human- and machine-readable.

On the operational side, the ATSC is working to finalize a recommended practice on DTV transport stream verification. Document PS-697, "Proposed ATSC Recommended Practice: Transport Stream Verification," outlines a common methodology for describing transport stream conformance criteria.

This document explicitly describes the elements and parameters of ATSC Standards A/53 and A/65 that should be verified in a transport stream for it to be considered a proper emission. The document does not cover RF, captioning, or elementary streams.

PS-697 has been approved by a letter ballot of the ATSC Technology and Standards Group and will go before the ATSC membership for final approval shortly. If all goes as expected, PS-697 could be approved and finalized before the end of the year.

While ATSC standards strictly define the contents and characteristics of the DTV emission transport stream, there may be a number of interactions and interrelationships amongst various components. Successful tuning and display of programs can be ensured if the transport stream adheres to the applicable specifications.

The Proposed Recommended Practice identifies transport stream issues by type, dividing errors into the general following categories:

• Program Specific Information (PSI) errors

• PSIP errors

• Timing model and buffering errors

• Consistency errors

• General errors

Each error type is provided with a defined "error severity," as detailed below:

• Transport stream off-air

• Program off-air

• Component missing

• Quality of service

• Technically nonconformant

Example error conditions for the PSIP Master Guide Table are in Table 3.

All ATSC standards, recommended practices, and informational documents are available for download at no charge from the ATSC Web site ( http://www.atsc.org ). For additional information on PSIP, visit http://www.psip.org.