Program and System Information Protocol
The Program and System Information Protocol (PSIP) is the protocol originally defined by General Instrument for the DigiCipher 2 system and later extended for the ATSC digital television system for carrying metadata about each channel in the broadcast MPEG transport stream of a TV station and for publishing information about television programs so that viewers can select what to watch by title and description.
What PSIP does 
PSIP can also send:
- the exact time referenced to UTC and GPS time;
- the short name, which some stations use to publish their callsign. A maximum of seven characters can be used in a short name.
PSIP is defined in ATSC standard A/65, the most recent revision of which is A/65C, published in 2006. A/69 is a recommended practice for implementing PSIP in a TV station.
PSIP also supersedes the A/55 and A/56 protocol methods of delivering program guide information (which the ATSC has deleted). TV Guide On Screen is a different, proprietary system provided by datacasting on a single station, while PSIP is required, at least in the United States, to be sent by every digital TV station.
PSIP information may be passed through the airchain using proprietary protocols or through use of the XML-based Programming Metadata Communication Protocol (PMCP, or ATSC A/76) facility metadata scheme.
Included tables 
- STT (system time table)¹ - current time, transmitted at least once per second, with an accuracy of new time values within 1 second or better
- MGT (master guide table)¹ - data pointers to other PSIP tables
- TVCT (terrestrial virtual channel table)¹ - defines each virtual channel and enables EITs to be associated with the channel
- CVCT (cable virtual channel table) - assigns numbers to each virtual channel and enables EITs to be associated with the channel
- RRT (rating region table) - content ratings for each country (region) covered by the station, save the U.S., as that region is loaded into TV sets already
- EIT (event information table)¹ - titles and program guide data
- ETT (extended text table) - detailed descriptions of channels (Channel Extended Text Table or CETT) and aired events (Event Extended Text Table or EETT)
- DCCT (directed channel change table) - see below
- DCCSCT (directed channel change selection code table) - provides for the ability to update states, counties and program genres used in DCCT tables
¹ indicates a US FCC requirement
Directed channel change 
The DCC function lets broadcasters tell a DTV receiver where to change, based upon the viewer's settings. This is most likely to be a ZIP or other postcode, which can select demographically-based programming to show, such as television commercials or weather bulletins, possibly taken from an accompanying datacasting channel.
Implementation of the DCC feature is entirely optional, and depends on development of receiver and decoder technology. For example, a digital video recorder could record commercials broadcast at other times for later replay, so that many more different commercials could be shown in different parts of a large metro area than can actually be transmitted at once.
See also 
- EPG - Electronic program guide
- ATSC Standard A/65: Program and System Information Protocol
- ATSC Standard A/76 Programming Metadata Communications Protocol (PMCP) for transmitting PSIP data between devices in a broadcast facility
- ATSC Recommended Practice A/69: Program and System Information Protocol Implementation Guidelines for Broadcasters
- http://www.etherguidesystems.com/help/sdos/atsc/Syntax/TableSections/Default.aspx: for online details of PSIP table sections