Frequencies and Timings
Each MF tone consists of two frequencies, shown in the table on the left. Note that these are not the same as customer dialed Touch Tone, which is shown by the table on the right:
| Operator (blue box) dialed MF frequencies | ||||||
| Code | 700 Hz | 900 Hz | 1100 Hz | 1300 Hz | 1500 Hz | 1700 Hz |
|---|---|---|---|---|---|---|
| 1 | X | X | ||||
| 2 | X | X | ||||
| 3 | X | X | ||||
| 4 | X | X | ||||
| 5 | X | X | ||||
| 6 | X | X | ||||
| 7 | X | X | ||||
| 8 | X | X | ||||
| 9 | X | X | ||||
| 0/10 | X | X | ||||
| 11/ST3 | X | X | ||||
| 12/ST2 | X | X | ||||
| KP | X | X | ||||
| KP/ST2 | X | X | ||||
| ST | X | X | ||||
| Customer-dialed Touch-Tone (DTMF) frequencies | ||||
| 1209 Hz | 1336 Hz | 1477 Hz | 1633 Hz | |
|---|---|---|---|---|
| 697 Hz | 1 | 2 | 3 | A |
| 770 Hz | 4 | 5 | 6 | B |
| 852 Hz | 7 | 8 | 9 | C |
| 941 Hz | * | 0 | # | D |
Normally, the tone durations are on for 60ms, with 60ms of silence between digits. The 'KP' and 'KP2' tones are sent for 100ms. KP2 (ST2 in the R1 standard) was used for dialing internal Bell System telephone numbers. However, actual frequency durations can vary depending on location, switch type, and the machine status.
Read more about this topic: Blue Box