7.1 Call Analysis

E-1, T-1 and Analog telephony protocols may transmit in-channel call analysis information through the network via tones. Other protocols such as IP, ISDN, and SS7 utilize packetized messages to convey call analysis information, and others use CAS line signaling. For the purposes of this discussion call analysis refers to the detection and notification of these tones.

Call analysis consists of both pre-connect and post-connect information about the status of the call:

• Pre-connect information (call progress) determines the status of the call connection, that is, busy, no dial tone, no ring back, etc.
• Post-connect information (media type detection) determines the destination party's media type, for example, voice, answering machine or fax modem. The gc_GetCallInfo( ) function is used immediately following the receipt of a GCEV_CONNECTED event to retrieve this post-connect information notifying of the media type of the answering party. See the Global Call API Library Reference for more information.

Call analysis tones such as dial tone, ringback, busy and fax are defined either in the firmware, (Global Tone Detection and Global Tone Generation), or in the .cdp file (for E-1/T-1 and Analog technologies), or a combination of both. Tones defined in the firmware can be enabled or disabled by configuring parameters in the DX_CAP (call analysis parameter) data structure. Similarly, the DX_CAP data structure can be used to configure the voice detection algorithm which distinguishes answering machine or human speech. The default parameter values defined in the DX_CAP data structure can be changed by the gc_LoadDxParm( ) function to fit the needs of your application. For a detailed description of enhanced call analysis (PerfectCall) and how to use call analysis, see the Call Analysis topic in the Voice API Programming Guide. For a detailed description of the gc_LoadDxParm( ) function, see the Global Call API Library Reference for more information.

Some example uses of call progress tones are as follows:

• By detecting the ringback tone, the Global Call API can count the rings and report a GCEV_DISCONNECTED event when the call is not answered within the specified number of rings.
• For telephone circuits that include analog links, the local line may not have access to all of the digital signaling information. If so, the user must modify the country dependent protocol (.cdp) file accordingly to detect or generate the busy, ringback or dial tone of the native country.

Call analysis configuration and behavior is unique to each technology and protocol type. See the following for more information:

• For Analog PDK protocols, see the Global Call Analog Technology User's Guide.
• For ICAPI and E-1/T-1 PDK protocols, see the Global Call E-1/T-1 CAS/R2 Technology User's Guide.

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