phone networks

phone networks

If you remove the plastic shell from a phone made before about 1982, you'll probably see a little metal box with a plastic top holding a bunch of screws; and there are wires going from those screws to other parts of the phone, including the dial, hookswitch, handset and line cord.

That metal can is called a network (same word but different meaning than networks used to carry data and phone conversations around the world). A telephone's network holds various dull but critical components such as capacitors and coils that connect the external components, and help the phone connect to the outside world. If you open up the network, prepare to clean your hands, because it's filled with goo, like Vaseline, to protect the guts from humidity and temperature extremes.

Various models were made over the years. In about 1980, the Western Electric (AT&T) 425K network (third from top) replaced the 425G above it, with added connections to handle a touchtone dial. Other versions were made to fit smaller Princess and Trimline phones, and with special functions such as to fight interference from nearby radio transmitters.

In the 1980s, the goo-filled metal boxes were replaced by networks on printed circuit boards (bottom) which saved space and weight; and some recent phones have the network combined with the touchtone dial. Western Electric apparently changed to printed circuit networks after its smaller competitors.

Until the 1990s, the networks made by Western Electric, ITT, Stromberg-Carlson and Northern Telecom were virtually identical (because Western Electric licensed its designs to the others). In later years, each company developed its own designs, but they did not vary much.