First Real-Time Speech Communication on Packet Networks

In August 1974, the first real-time speech communication over a packet-switched network was demonstrated via ARPANET between MIT Lincoln Laboratory and USC Information Sciences Institute. By 1982, these technologies enabled Internet packet speech and conferencing linking terrestrial, packet radio, and satellite networks. This work in real-time network protocols and speech coding laid the foundation for voice-over-internet-protocol (VoIP) communications and related applications including Internet videoconferencing. This pioneering work on speech in packet networks developed and demonstrated systems which were forerunners of the voice-over internet protocol (VoIP) systems that are now so widely in use. The real-time voice work included development of a new Network Voice Protocol (NVP), because the packet and reliability constraints of the available Transmission Control Protocol (TCP) implementation made it unsuitable for real-time communication. This protocol development was an immediate forerunner of the separation of TCP and IP, so that the real-time packet speech work played a large role in the development of the protocols, which are still in wide use today. The technology and protocols for real-time speech over packet networks also enabled other real-time internet applications such as packet video, so that now systems like Skype enable real-time voice and video at home and in offices for extremely large number of people. This work combined major developments in multiple areas, including the first real-time implementations of narrowband LPC speech coding on digital signal processors, network protocols to enable real-time packet delivery, strategies for reconstituting speech, techniques for reconstitution of speech from packets arriving at non-uniform intervals, packet speech conferencing techniques, and interoperation over different types of packet networks (landline, Ethernet, satellite, radio). Another feature was the outstanding collaboration among organizations and across technology areas. Finally, the long-term impact is a major feature which sets this work apart, as evidenced by the wide use of VoIP and related application such as packet video.