1A Voice Storage System: Prologue
G. D. Bergland, W. T. Hartwell, Grimmond Smith · Bell System Technical Journal · 1982
In modern times, distant voice communication in the United States has been predominantly by telephone. There are some applications for which voice is recorded, transmitted (perhaps by mail), and replayed, but this form of “taped letter” is the exception rather than the rule. A constraining factor when communicating by telephone is that both the calling and called parties must simultaneously be available. The probability of a successful call completion is approximately 0.75. Unfortunately, the successful completion is often to the desired line but not to the desired terminating party and, thus, additional calls are required to complete the communication.