Network Voice Protocol

The Network Voice Protocol (NVP) was an important early way to send human speech over computer networks. It worked by breaking voice into small pieces called packets, which could travel across the network. This was one of the first examples of a technology called Voice over Internet Protocol, which lets people talk to each other using internet connections instead of traditional phone lines.

NVP helped show how voice could be sent through packetized communications networks. This was a big step in developing the ways we communicate today, making it possible for people to make voice calls over the internet.

History

NVP was first created and put into use in 1974. It was developed by the “Speech” project at ISI, the USC Information Sciences Institute, starting in December 1973. The project was led by Danny Cohen at the Information Sciences Institute of the University of Southern California, with support from ARPA's Network Secure Communications program. The goal was to show that secure, clear, and low-bandwidth voice communication could work over computer networks.

The first demonstration of NVP happened in August 1974 between ISI and MIT Lincoln Laboratory. This was the first time a “phone call” was made using a computer network. Researchers worked together from many places to make this happen. NVP used different ways to change speech into digital signals, including linear predictive coding and continuously variable slope delta modulation. Later, it was used for experiments with early video conferencing tools along the US East and West Coasts.

Protocol

The Network Voice Protocol (NVP) had two main parts: control protocols and a data transport protocol. The control protocols handled basic features like showing who wants to talk, playing ring tones, deciding how to encode voice, and ending calls. The data messages carried encoded speech. Each way of encoding speech had a specific packet size for sending voice samples.

NVP used the Internet Stream Protocol (ST) and a later version called Stream Protocol, version 2 (ST-II). Both of these were versions of the Internet Protocol (IP) that focused on keeping connections stable. They were early tests of ways to manage network quality and connections, similar to later technologies like Asynchronous Transfer Mode (ATM).