Voice API Programming Guide — June 2005 79
Call Progress Analysis
Figure 6. A Standard Busy Signal
Figure 7. A Standard Single Ring
Figure 8. A Type of Double Ring
7.16.3 Elements of a Cadence
From the preceding cadence examples, you can see that a given cadence may contain two silence
periods with different durations, such as for a double ring; but in general, the nonsilence periods
have the same duration. To identify and distinguish between the different types of cadences, the
voice driver must detect two silence and two nonsilence periods in the audio signal. Figure9
illustrates cadence detection.
The timings are given in units of 10ms.
nonsilence
silence
50
50
50
50 50
50 50
The timings are given in units of 10ms.
nonsilence
silence
200 200
400
≈
≈
≈
The timings are given in units of 10ms.
nonsilence
silence
50
225
≈
50 50
25