Preview Dialer: In Preview mode, the agent starts by himself the next call (semi-automatic preview dialing) on a software-based selection process. The preview dialing ensures that the call center staff can preview the record from the customer database. If the agent triggers the call attempt by himself, he has also opportunity to prepare for the interview and detailed view (for example the contact history). The employee initiates the call either by using software or by manually dialing the telephone number.
Power Dialer: The dialer software automatically dials the next phone connection as soon as the processing of the previous record was completed by the agent. This can be done by the software on the client or on the central server. It can be set with an "overdial factor" that not only one but several telephone lines per agent get to be established. The dialing attempts are doing mostly displayed in the selection preview on the workplace of the agents. The first successful selection is presented. Other successful dialing attempts are distributed by chance on the next available agent. In the calculations involved, that usually not all numbers dialed indicate a dial tone, but might be busy or unavailable for other reasons.
Predictive Dialer: Even with predictive dialing the telephone numbers of the contact list or database of the company or service provider get selected automatically. In addition, the dialer software monitored by mathematical methods continually in several ways, such as the current availability or the average call duration of each employee, and includes this in the calculation for the selections. The Predictive dialing is thus a forward-looking, self-adjusting dial. The predictive dialer controls the number of dial attempts per agent, taking into account the current and historical accessibility of customers and on the basis of the derived prediction. This not only minimizes the waiting time between two contacts of the agent, but also provides the ideal case that as many calls as possible are made without call attempts must be canceled. Lost connections causing the called phone rings, after picking up is no caller on the other end available or it rings only for a very short time (dropped call). Consumers perceive this as harassing or threatening.
In the UK, Ofcom requires that predictive dialers abandon less than 3% of answered calls on a daily basis. Ofcom also requires that if an agent is not available within 2 seconds the call is considered "abandoned" and an automated message is played. The automated message must identify the company making the call, the purpose of the call, a free phone or basic rate phone number to call back on and must not contain any form of marketing. A phone call to the return number must not be treated by the company as an opportunity to market, but to be removed from the calling list. In the UK "abandoned" calls must not be called back within 72 hours unless there is a dedicated agent available.
In the USA, if someone answers but no agent is available within 2 seconds of the person's greeting, Federal Communications Commission (FCC) regulations consider the call "abandoned" and require the dialer to play a recorded message. The FCC requires that predictive dialers abandon less than 3% of answered calls.
In Canada, the maximum abandon rate is 5%, and calls cannot be made to numbers registered with the National Do Not Call Registry, emergency or health care providers.