Which technology allows the use of the Internet for real-time voice and video communication?

VoIP, or Voice over Internet Protocol, is the technology that enables voice communication to be transmitted over the Internet in real-time. It converts analog voice signals into digital data packets, allowing voice calls to be made over the Internet rather than using traditional telephone lines. This technology supports not just voice calls but also integrates video communication, making it ideal for both personal and business interactions.

In contrast, ISDN (Integrated Services Digital Network) is a circuit-switched telephone network system that allows for simultaneous digital transmission of voice, video, data, and other services. However, it does not use the Internet for this but rather relies on dedicated telephone lines.

Fax over IP refers specifically to the transmission of fax documents over the Internet, which does not encompass real-time voice or video communication.

Video conferencing typically employs VoIP technology for its audio components but is more focused on the visual aspect of communication. While it provides a platform for video calls, it relies on the protocols that VoIP establishes but does not define the foundational technology used for voice communication.

Thus, VoIP is the most comprehensive and suitable answer, as it directly addresses the need for both voice and video communication over the Internet in real-time.