Predictive Dialing - Telephony API Programmer's Reference

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Predictive Dialing

Predictive dialing is an application that typically runs on a call center telephony server. It uses a list of phone numbers, often obtained from a database, to attempt outbound calls; when a call is completed, the call is automatically assigned to an agent for handling. The application can make use of a predictive dialing port on a switch, which is a device that can make outbound calls and has special abilities (through DSP, and so on) to detect call progress tones and other audible indications of call state. When a call is made on a predictive dialing port, it will typically be automatically transferred to another device on the switch when the call reaches a particular state or upon detection of a particular media mode; this target device might be a queue for agents handling outbound calls.

Applications identify a device as having predictive dialing capability by the LINEADDRCAPFLAGS_PREDICTIVEDIALER bit in the dwAddrCapFlags member in LINEADDRESSCAPS. The dwPredictiveAutoTransferStates member in LINEADDRESSCAPS indicates the states upon which the predictive dialing port can be commanded to automatically transfer a call; if this member is zero, it indicates that automatic transfer is not available, and that it is the responsibility of the application to transfer calls explicitly upon detecting the appropriate call state (or media mode or other criteria). Preferably, switch manufacturers will make available both automatic and manual transfer, and allow applications to select the preferred mechanism, but service providers would have to model the behavior of legacy equipment. A single predictive dialing port (line device/address) can support making several outbound calls simultaneously, as indicated by the dwMaxNumActiveCalls member in LINEADDRESSCAPS. Predictive dialing capability can also be made available on any device, using a shared pool of predictive dialing signal processors, which are bridged onto the line being dialed upon request.

When the lineMakeCall function is used on a line capable of predictive dialing (a port with the LINEADDRCAPFLAGS_PREDICTIVEDIALER set) and predictive dialing is requested using LINECALLPARAMFLAGS_PREDICTIVEDIAL, then the call is made in a predictive fashion with enhanced audible call progress detection. Additional fields and constants are defined in the LINECALLPARAMS structure passed in to lineMakeCall to control the behavior of the predictive dialing port. The dwPredictiveAutoTransferStates member indicates the line call states which, upon entry of the call into any of them, the predictive dialing port should automatically transfer the call to the designated target (the bits must be a proper subset of the supported auto-transfer states indicated in LINEADDRESSCAPS); the application can leave the field set to 0 if it desires to monitor call states itself and use lineBlindTransfer to transfer the call when it reaches the desired condition. The application must specify the desired address to which the call should be automatically transferred in the variable field defined by the dwTargetAddressSize and dwTargetAddressOffset members in LINECALLPARAMS.

Applications can also set a timeout for outbound calls so that the service provider will automatically transition them to a disconnected state if they are not answered. This is controlled using the dwNoAnswerTimeout member in LINECALLPARAMS.

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