A History of Realtime Digital Speech on Packet Networks: Part II of Linear Predictive Coding and the Internet Protocol

Abstract

In December 1974 the first realtime conversation on the ARPAnet took place between Culler-Harrison Incorporated in Goleta, California, and MIT Lincoln Laboratory in Lexington, Massachusetts. This was the first successful application of realtime digital speech communication over a packet network and an early milestone in the explosion of realtime signal processing of speech, audio, images, and video that we all take for granted today. It could be considered as the first voice over Internet Protocol (VoIP), except that the Internet Protocol (IP) had not yet been established. In fact, the interest in realtime signal processing had an indirect, but major, impact on the development of IP. This is the story of the development of linear predictive coded (LPC) speech and how it came to be used in the first successful packet speech experiments. Several related stories are recounted as well. This is the second part of a two part monograph on linear predictive coding (LPC) and the Internet protocol (IP). The first part presented an introduction to this history and a tutorial on linear prediction and its applications to speech, providing background and context to the technical history of the second part.