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Such an antecedent usually consisted of two closed-circuit television systems connected via coax cable or radio.
An example of that was the German Reich Postzentralamt (post office) video telephone network serving Berlin and several German cities via coaxial cables between 19.
Although not as widely used in everyday communications as audio-only and text communication, useful applications include sign language transmission for deaf and speech-impaired people, distance education, telemedicine, and overcoming mobility issues.
It is also used in commercial and corporate settings to facilitate meetings and conferences, typically between parties that already have established relationships.
This technique was very expensive, though, and could not be used for applications such as telemedicine, distance education, and business meetings.
By reducing the need to travel to bring people together, this technology also contributes to reductions in carbon emissions, thereby helping to reduce global warming.
The concept of videotelephony was first popularized in the late 1870s in both the United States and Europe, although the basic sciences to permit its very earliest trials would take nearly a half century to be discovered.
Only in the late 20th century with the advent of powerful video codecs combined with high-speed Internet broadband and ISDN service did videotelephony become a practical technology for regular use.
In the 1980s, digital telephony transmission networks became possible, such as with ISDN networks, assuring a minimum bit rate (usually 128 kilobits/s) for compressed video and audio transmission.
A videophone is a telephone with a video display, capable of simultaneous video and audio for communication between people in real-time.