Voice API Programming Guide — June 2005 73
Call Progress Analysis
7.15.1 Tri-Tone SIT Sequences
SIT frequency detection operates simultaneously with all other call progress analysis detection
methods. The purpose of frequency detection is to detect the tri-tone special information tone (SIT)
sequences and other single-frequency tones. Detection of a SIT sequence indicates an operator
intercept or other problem in completing the call.
SIT frequency detection can detect virtually any single-frequency tone below 2100 Hz and above
300 Hz.
Table8 provides tone information for the four SIT sequences on Springware boards. The
frequencies are represented in Hz and the length of the signal is in 10 msec units. The length of the
first segment is not dependable; often it is shortened or cut.
On DM3 boards, SIT sequences are defined as tone IDs. For a definition of SIT sequences on DM3
boards, see Table5, “Special Information Tone Sequences (DM3)”, on page 54.
7.15.2 Setting Tri-Tone SIT Frequency Detection Parameters
On Springware boards, frequency detection on voice boards is designed to detect all three tones in
a tri-tone SIT sequence. To detect all three tones in a SIT sequence, you must specify the frequency
detection parameters in the DX_CAP for all three tones in the sequence.
To detect all four tri-tone SIT sequences:
1. Set an appropriate frequency detection range in the DX_CAP to detect each tone across all
four SIT sequences. Set the first frequency detection range to detect the first tone for all four
SIT sequences (approximately 900 to 1000 Hz). Set the second frequency detection range to
detect the second tone for all four SIT sequences (approximately 1350 to 1450 Hz). Set the
third frequency detection range to detect the third tone for all four SIT sequences
(approximately 1725 to 1825 Hz).
2. Set an appropriate detection time using the ca_timefrq and ca_mxtimefrq parameters to detect
each tone across all four SIT sequences. For each tone, set ca_timefrq to 5 and ca_mxtimefrq
to 50 to detect all SIT tones. The tones range in length from 27 to 38 (in 10 msec units), with
some tones occasionally cut short by the Central Office.
Note: Occasionally, the first tone can also be truncated by a delay in the onset of call
progress analysis due to the setting of ca_stdely.
Table8. Special Information Tone Sequences (Springware)
SIT 1st Segment 2nd Segment 3rd Segment
Name Description Freq. Len. Freq. Len. Freq. Len.
NC No Circuit Found 985 38 1429 38 1777 38
IC Operator
Intercept
914 27 1371 27 1777 38
VC Vacant Circuit 985 38 1370 27 1777 38
RO Reorder
(system busy)
914 27 1429 38 1777 38