Terms

Call Progress Tone Patterns

Call progress tone patterns are audible signals that indicate the progress or disposition of a telephone call. Examples of call progress tone patterns include the busy signal, ringback, and dial tone.

Call Progress Analysis (CPA)

The act of receiving and interpreting call progress tone patterns is called Call Progress Analysis (CPA).

For call progress analysis, the CSP groups patterns into classes to facilitate management of CPA receivers. These CPA classes help assign call progress tone patterns to CPA receivers. When the host assigns a DSP resource to scan for call progress tones, the host specifies a class of patterns. The DSP resource then scans for the patterns defined in that class.

For example, you could place all progress tones used in a single country into one class. You could then assign this class to a DSP chip for call progress analysis for that country. The host can modify and create classes, using the CPA Pattern Configure message.

When a Call Processing receiver activates, it detects call progress patterns that are part of a Call Progress Analysis (CPA) Class. The receiver ignores any tones that are not part of a pattern in this CPA Class. This scenario allows the receiver to skip over tones that are not of interest, reducing the chance of receiving false Call Progress Analysis Result API messages.

By default, the CSP uses the following four CPA classes:

• 0x00 Standard North America

• 0x01 Dial Tone

• 0x02 CPC Detection

• 0x03 Energy Detection

Frequency

A frequency is the most basic building block of a call progress tone pattern.

Tone

A tone is a combination of frequencies, or it is a single frequency that has been designated as a tone. The frequency or frequencies in a tone have specified dBm levels.

Tone Pattern

A tone pattern is a single tone or a sequence of tones, divided at precise intervals by silence. A tone pattern is formed when tones are combined, with specific intervals of silence between them.

For example, the industry-standard "call waiting tone" is actually a pattern, in which Tone 1 is on for 300 milliseconds, off for 9700 milliseconds, and on again for 300 milliseconds. You can think of a call progress tone pattern as being at the top of a hierarchy, with tone in the middle and frequency at the bottom. That is, one or more frequencies make up a tone, and one or more tones make up a pattern.

Figure 8-4 The Composition of a Call Progress Tone Pattern