more at http://phones.quickfound.net/ "ELECTRO-MAGNETIC THEORY AS APPLIED TO TELEPHONY; COMPONENTS, OPERATION AND TRANSMISSION RANGE OF SOUND POWERED, LOCAL BATTERY, AND COMMON BATTERY TELEPHONIC SYSTEM." US Army Training Film TF11-3116 Reupload of a previously uploaded film, in one piece instead of multiple parts, and with improved video & sound. Public domain film from the US National Archives, slightly cropped to remove uneven edges, with the aspect ratio corrected, and one-pass brightness-contrast-color correction & mild video noise reduction applied. The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original). http://creativecommons.org/licenses/by-sa/3.0/ http://en.wikipedia.org/wiki/Telephony In telecommunications, telephony encompasses the general use of equipment to provide communication over distances, specifically by connecting telephones to each other. The technology is associated with the electronic transmission of voice, fax, or other information between distant parties using systems historically associated with the telephone, a hand-held device containing both a speaker or transmitter and a receiver. It is commonly referred to as the construction or operation of telephones or telephonic systems and as a system of telecommunications in which telephonic equipment is employed in the transmission of speech or other sound between points, with or without the use of wires.. To break the term down into further detail, telephony is the science of translating sound into electrical signals, transmitting them, and then converting them back to sound; that is, the science of telephones. The term is used frequently to refer to computer hardware and software that performs functions traditionally performed by telephone equipment. For example, telephony software can combine with your modem to turn your computer into a sophisticated answering service. A popular example of this type of telephony software is voice mail... Brief overview Telephones were originally connected directly together in pairs. Each user would have a separate telephone wired to various places he might wish to reach. This became inconvenient when people wanted to communicate with many other people using telephones, so the telephone exchange was invented. Each telephone could then be connected to other local ones, thus inventing the local loop and the telephone call. Soon, nearby exchanges were connected by trunk lines, and eventually distant ones were as well. In modern times, most telephones are plugged into telephone jacks. The jacks are connected by inside wiring to a drop wire which connects the building to a cable. Cables usually bring a large number of drop wires from all over a district access network to one wire center or telephone exchange. When the user of a telephone wants to make a telephone call, equipment at the exchange examines the dialed telephone number and connects that telephone 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 telephone network (PSTN). By the end of the 20th century almost all were stored program control exchanges. After the middle of the 20th century, fax and data became important secondary users of the network created to carry voices, and late in the century, parts of the network were upgraded with ISDN and DSL to improve handling of such traffic. Today, telephony has been digitized and has merged into digital telephony,.. Another important concept that has been merged into telephony is computer telephony integration, which enables computers to know about and control phone functions such as making and receiving voice, fax, and data calls with telephone directory services and caller identification...

• published: 01 Oct 2015
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