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Call Progress Analysis and Color Ring Back Tones


How to Avoid Call Progress Analysis Mis-detections when Color Ring Back Tone (CRBT) is Provided

Issue:
As Color Ring Back Tone (CRBT or musical ring back) becomes more and more popular among cell phone users, there is a challenge of how to avoid detecting the CRBT as VOICE/AM yet still have accurate and dependable Call Progress Analysis (CPA) results. While it is NOT possible to disregard the CRBT, it is possible to code the application to work around these tones.

Work-around / Solution:
The application will need to monitor when the call progress result compared to the signaling events being returned. This method can only be used with the DX method of initializing CPA because the Global Call (GC) method does not provide the necessary flexibility of the DX method. By not allowing a post-connect result to return before a CONNECTED event, this will by-pass the CRBT to get to the true call result.

Pseudo-code on the process:
-Issue make call

-Initialized CPA via the DX method during the one of the signaling events: ALERTING / PROCEDING / PROGRESSING

-IF a pre-connect detection is made (busy, SIT, RNA) BEFORE the CONNECTED event is received then result is assumed to be correct and should be kept.

-ELSE IF a post connect detection is made AFTER the CONNECTED event is received then result is assumed to be correct and should be kept.

-ELSE IF a post connect detection is made (cadence break, voice or AM) BEFORE the CONNECTED event is received then the result is assumed to be incorrect. Call Progress should be stopped and the result should be discarded. Restart CPA again once the CONNECTED event is received and wait for next Call Progress result.

Note: this work-around cannot be used in conjunction with analog or line-side T1 because of the lack of line signaling events.

Dialogic Product List:
• DM3
• SPWR
• HMP / IP

Glossary of Acronyms / Terms

• Call Progress Analysis (CPA) – the process of detecting pre-connect information about failed outbound call attempts and the destination party’s media type for connected outbound calls. 

• Color Ring Back Tone (CRBT) – the substitution of music or other non-standard tones for indicating ring back.

• Global Call CPA — Global Call API function calls perform CPA using an attached voice device and report CPA results via the GCEV_MEDIADETECTED and GCEV_DISCONNECTED events.

• Voice API CPA — The Voice API dx_dial() function performs CPA using a voice resource directly and reports results via the TDX_CALLP event.

Related Links:

Call Progress Analysis: Global Call API Usage and Protocol Configuration App Note
http://www.dialogic.com/network/csp/appnots/10117_CPA_SR6_HMP2.pdf

First Published
• March 26th 2007

Last Updated
• March 26th, 2007







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