Direct Distance Dialing: Call Completion and Customer Retrial Behavior

Each day Bell System customers initiate about 780 million telephone call attempts to be carried from one part of the telephone network to the other. A very sophisticated network has been engineered to carry 295 both local and toll calls. Though only 7 percent of those calls are toll calls, the number of toll calls is still very large indeed. For instance, on an average business day in 1977 about 52 million toll call attempts were placed by customers. Of those attempts, 36 million toll attempts (roughly 70 percent) led to successful telephone connections, with the other 16 million attempts resulting in failures because of the called customer being busy or not in, circuit blockage, and so on. A customer does not always succeed in establishing a desired connection on the initial attempt. Some customers will abandon their effort to establish desired connections after encountering incomplete attempts, others will make additional attempts. Therefore, a desired connection may lead to a sequence of more than one attempt, ultimately resulting in a connection or abandonment by the calling customer. Whether each attempt will result in a successful completion depends not only on network-dependent variables such as engineered blocking level, but also on customer-controlled variables such as telephone usage and on interactions between the two groups of variables. The main purpose of this study is to obtain results needed to characterize both network performance and customer behavior not only on initial attempts but also on possible subsequent attempts in setting up a desired telephone connection.