There are two types of Predictive Dialers: Soft Dialers and Hard Dialers.
Soft Dialers have all dialing algorithms soft, the vendor supplies the software.
The algorithms interface via a Computer Telephony Integration (CTI) port on a switch that does the dialing. Integrated Service Digital Network (ISDN) messaging or a CTI link is used for call progress analysis. ISDN can provide digital code indicating the type of non-connect.
It allows a switch to filter out all calls which are non-connects. One doesn't have to listen to special tones to detect whether call is busy or un-obtainable. Thus all non-connects are eliminated and the right reason codes are passed to the software application, and the future course of action on the call can be taken.
But the advantages are few and are still preferred because they are cheaper, do not require expensive telephony components, and are flexible enough to work in multisite and distributed environments.
The major disadvantage being it relies on Answering Machine Detection (AMD) and call progress detection capabilities of the underlying PBX/switch platform.
Hard Dialers use dedicated telephony switches to detect answering machines and carry out call progress analysis. The dialer vendor provides the dialer server too.
In the agent audio type of connection of the switch, as soon as the agent logs in for his session, the dialer places a call to the agents desk. This connection is then left open for the rest of his or her session.
The external audio type of connection is used to make outbound phone calls. As soon as the outbound call is made and answered, it is immediately joined to an already open agent audio connection of the agent selected to take the call.
The advantages are many when compared with soft dailers. In hard dialers the audio connections can go directly to the PSTN while in soft dialers these are connected to PBX. Hard Dialers do not need upgrading and are unaffected by software changes. The AMD and call progress detecting abilities are far superior. The major disadvantage being more expensive and suitable for large call centres.