0-9 | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z
A signal sent from the called to the calling station, i.e., from the original data sink to the original data source. (188) Note: Backward signals are usually sent via a backward channel and may consist of supervisory, acknowledgment, or control signals.