Voice API Programming Guide — June 2005 67
Call Progress Analysis
7.11.3 Dial Tone Detection
Wherever call progress analysis is in effect, a dial string for an outgoing call may specify special
ASCII characters that instruct the system to wait for a certain kind of dial tone. The following
additional special characters may appear in a dial string:
L
wait for a local dial tone
I
wait for an international dial tone
X
wait for a special (“extra”) dial tone
The tone definitions for each of these dial tones is set for each channel at the time of the
dx_initcallp() function. In addition, the following DX_CAP fields identify how long to wait for a
dial tone, and how long the dial tone must remain stable.
ca_dtn_pres
Dial Tone Present: the length of time that the dial tone must be continuously present (in 10
msec units). If a dial tone is present for this amount of time, dialing of the dial string proceeds.
Default value: 100 (one second).
ca_dtn_npres
Dial Tone Not Present: the length of time to wait before declaring the dial tone not present (in
10 msec units). If a dial tone of sufficient length (ca_dtn_pres) is not found within this period
of time, call progress analysis terminates with the reason CR_NODIALTONE. The dial tone
character (L, I, or X) for the missing dial tone can be obtained using ATDX_DTNFAIL( ).
Default value: 300 (three seconds).
ca_dtn_deboff
Dial Tone Debounce: the maximum duration of a break in an otherwise continuous dial tone
before it is considered invalid (in 10 msec units). This parameter is used for ignoring short
drops in dial tone. If a drop longer than ca_dtn_deboff occurs, then dial tone is no longer
considered present, and another dial tone must begin and be continuous for ca_dtn_pres.
Default value: 10 (100 msec).
7.11.4 Ringback Detection
Call progress analysis uses the tone definition for ringback to identify the first ringback signal of an
outgoing call. At the end of the first ringback (that is, normally, at the beginning of the second
ringback), a timer goes into effect. The system continues to identify ringback signals (but does not
count them). If a break occurs in the ringback cadence, the call is assumed to have been answered,
and call progress analysis terminates with the reason CR_CNCT (connect); the connection type
returned by the ATDX_CONNTYPE( ) function will be CON_CAD (cadence break).
However, if the timer expires before a connect is detected, then the call is deemed unanswered, and
call progress analysis terminates with the reason CR_NOANS.
To enable ringback detection, turn on SIT frequency detection in the DX_CAP ca_intflg field. For
details, see Section 7.10.2, “Setting Up Call Progress Analysis Features in DX_CAP”, on page 61.