Graphical Approach to PSIP Consistency Checking

In order for ATSC DTV receivers to operate properly, the PSIP/PSI data in the broadcast stream must be correct, complete, and internally consistent. This paper describes a graphical approach to showing the interrelationships among the PSIP/PSI tables in a DTV broadcast stream and highlighting any inconsistencies. Key aspects of this approach are: (1) the use of color coding to provide an “at a glance” indication of which table sets have problems, (2) the use of color coding to highlight relationships among tables, (3) the use of color coding to highlight relationships between tables and the corresponding entries in an electronic program guide display, (4) the use of color coded “pseudotables” to indicate graphically any missing tables. INTRODUCTION TO PSIP/PSI A digital television (DTV) broadcast stream consists of a sequence of MPEG-2 transport stream packets, each of which is 188 bytes long, with a 4-byte header and a 184-byte payload. The broadcast stream may contain multiple virtual channels. Some of these may be video channels, which contain a video stream and possibly one or more audio and/or data streams. Some may be audio channels, which contain at least one audio stream and possibly additional audio and/or data streams. Some may be data channels, which just contain one or more data streams. In the header of each transport stream packet there is a PID (packet identifier) field that identifies which stream that packet belongs to. For example, a video channel might have one PID for video, another PID for English-language audio, and another PID for Spanish-language audio, etc. The sequence of packets with a given PID value is often called a PID stream. A DTV broadcast stream also contains metadata that describe the virtual channels in the broadcast and the programming in those virtual channels. For ATSC DTV broadcasts these metadata are defined in the MPEG-2 Systems Standard and the ATSC PSIP Standard. The PSI (Program Specific Information) tables defined in the MPEG-2 Systems Standard provide very basic information about the virtual channels and their components. However, receivers need the more complete information provided by the PSIP (Program and System Information Protocol) tables defined in the ATSC PSIP Standard in order to provide the tuning, branding and program promotion features that are key elements of the digital television viewing experience. Tuning The PSI tables and the PSIP tables both list the virtual channels in the broadcast stream, identify the PID streams that make up each virtual channel, and give some basic information about these PID streams, such as the type of each stream (video, audio, or data). They also give the language of the audio streams, so that a receiver can select the language stream that matches the viewer preferences, as specified by the user during the set-up of the receiver. The PSIP tables provide additional, critical information about closed caption services and content advisory ratings (so-called “V-chip” ratings), so that the receiver can select the closed caption service that matches the viewer preferences, and can decide which channels the viewer is allowed to tune to. Branding The PSIP tables carry information that allows viewers to select virtual channels by virtual channel number, rather than physical broadcast band. The virtual channel number is a two-part number, containing a major channel number and a minor channel number, and the broadcaster’s analog channel number is used as the major channel number. This arrangement allows broadcasters to preserve their investment in branding their analog TV channel number. The PSIP tables also carry a short channel name, up to seven characters long, that will typically be displayed by receivers on the screen for several seconds when a viewer selects the channel. It will also be used along with the virtual channel number to identify the channel in the receiver’s on-screen electronic program guide (EPG), thereby helping broadcasters leverage their investment in branding their call letters. Promotion The PSIP tables include brief information about each event (TV program) in the broadcast stream, such as the event title, start time, duration, closed caption indicator, stereo/surround indicator, and content advisory rating. They can also include extended text descriptions of each event and each virtual channel. Typically the brief information about the current event will be displayed by DTV receivers for a few seconds when a viewer switches to a new channel, and will be available on demand via a button on the remote control. It will also be displayed in the EPG. The more detailed