The device can map these SIT tones to a Q.850 cause and then map them to SIP 5xx/4xx
responses, using the parameters SITQ850Cause, SITQ850CauseForNC,
SITQ850CauseForIC, SITQ850CauseForVC, and SITQ850CauseForRO.
Table 37-5: Special Information Tones (SITs) Reported by the device
Special
Information
Tones (SITs)
Name
Description First Tone
Frequency
Duration
Second Tone
Frequency
Duration
Third Tone
Frequency
Duration
(Hz) (ms) (Hz) (ms) (Hz) (ms)
NC1
No circuit found 985.2 380 1428.5 380 1776.7 380
IC
Operator intercept 913.8 274 1370.6 274 1776.7 380
VC
Vacant circuit (non
registered number)
985.2 380 1370.6 274 1776.7 380
RO1
Reorder (system
busy)
913.8 274 1428.5 380 1776.7 380
NC*
- 913.8 380 1370.6 380 1776.7 380
RO*
- 985.2 274 1370.6 380 1776.7 380
IO*
- 913.8 380 1428.5 274 1776.7 380
For example:
INFO sip:5001@10.33.2.36 SIP/2.0
Via: SIP/2.0/UDP 10.33.45.65;branch=z9hG4bKac2042168670
Max-Forwards: 70
From: <sip:5000@10.33.45.65;user=phone>;tag=1c1915542705
To: <sip:5001@10.33.2.36;user=phone>;tag=WQJNIDDPCOKAPIDSCOTG
Call-ID: AIFHPETLLMVVFWPDXUHD@10.33.2.36
CSeq: 1 INFO
Contact: <sip:2206@10.33.45.65>
Supported: em,timer,replaces,path,resource-priority
Content-Type: application/x-detect
Content-Length: 28
Type= CPT
SubType= SIT-IC
The X-Detect event notification process is as follows:
1. For IP-to-Tel or Tel-to-IP calls, the device receives a SIP request message (using the
X-Detect header) that the remote party wishes to detect events on the media stream.
For incoming (IP-to-Tel) calls, the request must be indicated in the initial INVITE and
responded to either in the 183 response (for early dialogs) or in the 200 OK response
(for confirmed dialogs).
2. Once the device receives such a request, it sends a SIP response message (using the
X-Detect header) to the remote party, listing all supported events that can be detected.
The absence of the X-Detect header indicates that no detections are available.
3. Each time the device detects a supported event, the event is notified to the remote
party by sending an INFO message with the following message body:
• Content-Type: application/X-DETECT
• Type = [CPT | FAX | PTT…]
• Subtype = xxx (according to the defined subtypes of each type)
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