CONTENTS

 1     General
 2     Electrical levels for tones
 3     Acoustical levels for tones
 4     Dial tone
 5     Ringing tone
 6     Busy tone and congestion tone
 7     Special information tone
 8     Warning tone to indicate that a conversation is being recorded
 9     Payphone recognition tone
        9.3     Duration and level
10     Call waiting tone
11     Caller waiting tone
12     Machine recognition of tones
Annex A  Digital generation of tones
Annex B  Examples for limitation of spurious components of the dial tone with respect to interference with the frequencies recommended for pushbutton telephone sets in Recommendation Q.23
        B.1     Method A (used by ATT)
        B.2     Method B (used by the Federal Republic of Germany)