TV Data Broadcasting -
Point-to-Multipoint Data Communications; explains principles of
VBI: uses lines 10 through 20, with line 21 used for closed-captioning.
Each VBI line carries a datarate of 288 bits per field, with 64 bits for
set-up and addressing, yielding a raw data rate of 185 kb/s. FEC reduces
the capacity to 150 kb/s.