Info

0.33 s

0.33 s

0.33 s

1.0 s

0.33 s *

"" 0.33 s " ► Time

Figure 3.4-2 Special information tone.

Figure 3.4-2 Special information tone.

Congestion-tone. This is sent by exchanges when the call cannot be set up because of congestion in the network (no outgoing trunk available). In the U.S. this tone is known as "reorder" tone. Some typical cadences are:

On (seconds) Off (seconds)

In a number of countries (Austria, Brazil, Italy, Russia, etc.), congestion is still indicated by busy-tone.

Special Information Tone (SIT). A cadenced sequence of three frequencies, as shown in Fig. 3.4-2. It is used in many European countries to indicate that the received called number is not a working number.

SIT and Recorded Announcement In the U.S., one cycle of SIT is often sent before an announcement that gives more details about the problem, for example: "Your call cannot be completed as dialed " In case that the called number of a subscriber has been changed, the new number is usually included in the announcement.

An extensive survey of tones and recorded announcements used in various countries can be found in [7].

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