System information (SI) is a tabular data format used by the digital receiver device to drive content navigation, tuning, and presentation. See Figure 5-1, which shows that the system information can be sent as part of the in-band digital channel. Cable systems can also transmit system information in an out-of-band channel, as described in Chapter 5, "Adding Digital Television Services to Cable Systems."
There are several standards for system information:
ATSC A/56Also known as SI, A/56 was adopted by the cable industry before it was made obsolete by ATSC. DVS-011 and DVS-022 are SCTE standards based on A/56; they are used for basic navigation functions. (Program guide information is sent separately in a proprietary format.)
DVS-234Also known as SI, DVS-234 is an SCTE-proposed standard that seeks to establish a common service information standard for out-of-band cable channels. (See the section Out-of-Band Channels in Chapter 16, "OCI-N: the Network Interface.")
ATSC A/65Also known as Program and System Information Protocol (PSIP), A/65 has been adopted for terrestrial digital broadcast. In addition to basic navigation functions (such as channel numbering), PSIP can carry content description information that can be used by the programmer to deliver information for electronic program guides. (See the section In-Band Channels in Chapter 16.)