On Hold Voice Over:

In telecommunication, on hold voice encompasses the general use of equipment to provide voice communication over distances, specifically by connecting telephones to each other.

On hold voice over originally were connected directly together in pairs. Each user had separate on hold voice over wired to the various places he might wish to reach. This became inconvenient when people wanted to talk to many other telephones, so the on hold voice over exchange was invented. Each on hold voice over could then be connected to other local ones, thus inventing the local loop and the on hold voice over call. Soon, nearby exchanges were connected together by trunk lines, and eventually far away ones were.

In modern times, most on hold voice over are plugged into on hold voice over jacks. Each jack is connected by inside wiring to a drop wire and then to a cable with other wires. Cables usually bring a large number of wires from all over a district to one wire center or on hold voice over exchange. When the user of a on hold voice over wants to make a on hold voice over call, equipment at the exchange examines the dialed on hold voice over number and connects that on hold voice over line to another in the same wire center, or to a trunk to a distant exchange. Most of the exchanges in the world are connected to each other, forming the Public Switched On hold voice over Network or PSTN. By the end of the 20th century almost all were Stored Program Control exchanges.

Digital telephony is the use of digital technology in the provision of on hold voice over services and systems. Almost all on hold voice over calls are provided this way, but sometimes the term is restricted to cases in which the last mile is digital, or where the conversion between digital and analog signals takes place inside the telephone. On hold voice over was digitized to cut the cost and improve the quality of voice services, but digital on hold voice over was then found useful for new network services (ISDN) to transfer data speedily over on hold voice over lines.

IP Telephony is a modern form of on hold voice over which uses the TCP/IP protocol popularized by the internet to transmit digitized voice data. Contrast this with the operation of POTS (an acronym for "Plain Old On hold voice over Service").

Computer On hold voice over Integration (CTI) enables computers to know about and control phone functions such as making and receiving voice, fax, and data calls with on hold voice over directory services and caller identification. The integration of on hold voice over software and computer systems is a major development in the evolution of the automated office.