Sonderinformationston

There are various tones that signal certain connection states to the telephone subscribers. The ringing tone is one such tone, the busy tone, dial tone, connection tone, hold tone and the special information tone are others.

The special information tone( SIT) signals to the subscriber that it is currently not possible to connect to the desired subscriber. This signal sequence, which consists of three short tones with increasing frequency, is often combined with the announcement: "No connection under this number". The frequency of the three 330 ms long tone sequences is 950 Hz, 1.4 kHz and 1.8 kHz. There is a 1000 ms pause between the tone sequences.