Special-Information-Tone Frequency Detection
01 September 1981
As part of the process of evaluating the end-to-end performance in the telephone network, a sample of call attempts is evaluated and the attempts are classified into several categories, such as completed, busy, recorded announcements, etc. To mechanize this classification process, a machine must have the ability to distinguish between completed calls and recorded announcements. Current planning for the mechanized systems envisions the use of special-information-tone (SIT) prefixes which are to be attached to recorded announcements and can then be automatically recognized by the mechanized classifier (as well as alert the customer to the fact that he is listening to a recorded announcement). By choosing four distinct SITS, each representing a certain category of recorded announcements, the classifier will have the ability to distinguish between these categories as well as to recognize a recorded announcement in general. The SIT is defined as a sequence of three consecutive tones. To get four distinct SITS five frequencies were chosen: f