Network Voice Protocol

NVP was first defined and implemented in 1974, with definition led by the “Speech” project at ISI, the USC Information Sciences Institute following initial work begun in 1973.

Necessary subnet (IMP-to-IMP) changes for real-time packet forwarding were discussed at ISI in March 1974, chaired by Bob Kahn, DARPA’s program director for the speech project.

NVP was used to send speech between distributed sites on the ARPANET using several different voice-encoding techniques, including linear predictive coding (LPC) and continuously variable slope delta modulation (CVSD).

[citation needed] NVP was used by experimental Voice Funnel equipment (circa February 1981), based on BBN Butterfly computers, as part of ongoing ARPA research into packetized audio.

Control protocols included relatively rudimentary telephony features such as indicating who wants to talk to whom; ring tones; negotiation of voice encoding; and call termination.