TeleTYpewriter (TTY) or Telecommunications Device for the Deaf (TDD) Bit Rate
| Technology | Max Rate | Max Rate | Year |
| TTY (V.18) | 45.4545 bit/s | 6 characters/s | 1994 |
| TTY (V.18) | 50 bit/s | 6.6 characters/s | 1994 |
| NTSC Line 21 Closed Captioning | 1 kbit/s | ~100 characters/s | 1976 |