National Datacast Incorporated (NDI) is a pioneer in data broadcasting. It is a for-profit subsidiary of the Public Broadcasting Service (PBS) which handles datacasting on PBS TV stations throughout the United States. Services using ATSC digital TV include MovieBeam and UpdateTV, for which bandwidth is leased by other companies.
National Datacast was formed in 1988 based on PBS' early work in closed captioning for the hearing impaired.
It uses line 21 and other vertical interval lines for data transmission.