ATSC standards are, by and large, modular in scope. One standard builds upon the functionality of another. This point is demonstrated in the development of the ATSC's latest Candidate Standard known as "Programming Metadata Communication Protocol" (PMCP).
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:
- Program management
- Listing services
- MPEG encoder
(click thumbnail)Table 1 - Key tables of the PSIP standard.To provide full functionality, the PSIP generator needs to convey information from these sources to the receiver in the consumer's home. To make this happen, the data must populate the appropriate tables of the ATSC Program and System Information Protocol (PSIP) standard (see Table 1).
PSIP is a critical element of digital television that provides the methodology for transporting DTV system information and electronic program guide data. Because PSIP and other DTV metadata is typically developed and/or processed by several separate systems, communicating the appropriate metadata to the PSIP generator can be problematic.
PMCP is intended to solve this problem by defining a method for communicating metadata for the PSIP generator. The overall goal is to ensure proper PSIP implementation while requiring minimum manual intervention by the broadcaster.
Equipment manufacturers, system designers and broadcasters can use the tools provided in PMCP to help achieve that goal. Although targeted primarily at PSIP, the schema is extensible for other types of metadata, and can be used for carrrying of private information within the current structure. The protocol is complementary to and references existing ATSC standards. It also supports the ISO V-ISAN standard for unique identification of program content.
PMCP communication is based on a protocol utilizing extensible markup language (XML) message documents and schema. XML is widely recognized as flexible and usable for various system architectures. Equally important, it is capable of deployment 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 so that it is both human and machine-readable.
PMCP is now at Candidate Standard status within the ATSC. The Candidate Standard phase signifies the specification has reached a level of maturity for possible trial implementations. As field results are gathered from such trials, the specification can be modified to address any problems found. Following a defined Candidate Standard period, the specification is expected to advance to a final, approved standard according to the normal ATSC process.
A companion "Guide to the Use of the PMCP Standard" is also planned. The Programming Metadata Communication Protocol Candidate Standard (document number CS/75) is available for download at www.atsc.org/standards.html.
Other important efforts currently underway in ATSC include:
• A/96, "Interaction Channel Protocols," which has been approved and published as ATSC's latest standard. A/96 defines the protocols and performance requirements of transport facilities for a return channel to support digital broadcast interactivity.
• Comparative testing of advanced video codecs is being conducted for a proposed enhanced transmission mode, including subjective evaluation of candidate systems. This work, carried out in specialists group T3/S6, is a key element in the emerging Enhanced-VSB system.
• Progress continues the development of a "Recommended Practice" for operation of multiple transmitter networks, including distributed networks, on-channel repeaters and translators. This effort is being carried out in T3/S9 and compliments Candidate Standard CS/110A, the "Synchronization Standard for Distributed Transmission."
• A draft voluntary "Recommended Practice on Receiver Performance Guidelines" has been developed that describes signal conditions under which DTV receivers are expected to function in the field. This work has taken place in the ATSC Specialists Group on Receivers, T3/S10.
All the current ATSC Standards, Recommended Practices and related Informational Guidelines are available ATSC's Web site: http://www.atsc.org