82 Voice API Programming Guide — June 2005
Call Progress Analysis
7.16.5 Setting Selected Cadence Detection Parameters
Only the most commonly adjusted cadence detection parameters are discussed here. For a complete
listing and description of the DX_CAP data structure, see the Voice API Library Reference.
You should only need to adjust cadence detection parameters for network environments that do not
conform to the U.S. standard network environment (such as behind a PBX).

7.16.5.1 General Cadence Detection Parameters

The following are general cadence detection parameters in DX_CAP:
ca_stdely
Start Delay: the delay after dialing has been completed and before starting cadence detection.
This parameter also determines the start of frequency detection and positive voice detection.
Default: 25 (10 msec units) = 0.25 seconds.
Be careful with this variable. Setting this variable too small may allow switching transients or,
if too long, miss critical signaling.
ca_higltch
High Glitch: the maximum nonsilence period to ignore. Used to help eliminate spurious
nonsilence intervals. Default: 19 (in 10 msec units).
To eliminate audio signal glitches over the telephone line, the parameters ca_logltch and
ca_higltch are used to determine the minimum acceptable length of a valid silence or
nonsilence duration. Any silence interval shorter than ca_logltch is ignored, and any
nonsilence interval shorter than ca_higltch is ignored.
ca_logltch
Low Glitch: the maximum silence period to ignore. Used to help eliminate spurious silence
intervals. Default: 15 (in 10 msec units).

7.16.5.2 Cadence Detection Parameters Affecting a No Ringback

After cadence detection begins, it waits for an audio signal of nonsilence. The maximum waiting
time is determined by the parameter ca_cnosig (continuous no signal). If the length of this period of
silence exceeds the value of ca_cnosig, a no ringback is returned. Figure11 illustrates th is. This
usually indicates a dead or disconnected telephone line or some other system malfunction.
ca_cnosig
Continuous No Signal: the maximum time of silence (no signal) allowed immediately after
cadence detection begins. If exceeded, a no ringback is returned. Default: 4000 (in 10 msec
units), or 40 seconds.