Telephone switchboard in the context of Almon Strowger

A rotary dial is a component of a telephone or a telephone switchboard that implements a signaling technology in telecommunications known as pulse dialing. It is used when initiating a telephone call to transmit the destination telephone number to a telephone exchange as a succession of individual digits.

On the rotary dial, the digits are arranged in a circular layout, with one finger hole in the finger wheel for each digit. For dialing a digit, the wheel is rotated against spring tension with one finger positioned in the corresponding hole, pulling the wheel with the finger to a stop position given by a mechanical barrier, the finger stop. When released at the finger stop, the wheel returns to its home position driven by the spring at a speed regulated by a governor device. During this return rotation, an electrical switch interrupts the direct current (DC) of the telephone line (local loop) the specific number of times associated with each digit and thereby generates electrical pulses which the telephone exchange decodes into each dialed digit. Thus, each of the ten digits is encoded in sequences to correspond to the number of pulses; thus, the method is sometimes called decadic dialing. Pulse count dialing is a digital addressing system which uses decimal pulse count modulation. The typical average baud rate is 10 bits per second, though the system will usually accept from about 9 through 13 pulses per second, a requirement due to variations in the rotary dial mechanism governor speed.

A telephone call, phone call, voice call, or simply a call, is the use of a connection over a telephone network between two parties for audio communication. To start a call, the calling party, the caller, opens a connection for a particular phone number and waits for an answer to the request; often indicated by an audible ringtone. To answer the call, the called party accepts the request to start a conversation. A party is most commonly a single person, but can be a group of people (i.e. conference call) or a machine (i.e. fax). In some contexts, the term A-Number refers to the caller and B-Number refers to the called party.

The telephone call was enabled by multiple inventions in the mid- to late-19th century including the telephone. Initial technology involved point-to-point electrical wire connections between telephone installations, until centralized exchanges evolved where telephone operators established each interconnection manually at a telephone switchboard after asking the calling party for their call destination. After the invention of automatic telephone exchanges in the 1890s, the process became increasingly automated, eventually leading to the widespread adoption of digital exchanges in the second half of the 20th century, including the transition to wireless communication via mobile telephone networks and cellular networks. With the development of the Internet, the cost of telephone calls was drastically reduced with Voice over Internet Protocol (VoIP).

In the early days of telephony, companies used manual telephone switchboards, and switchboard operators connected calls by inserting a pair of phone plugs into the appropriate jacks. They were gradually phased out and replaced by automated systems, first those allowing direct dialing within a local area, then for long-distance and international direct dialing.

A phone connector is a family of cylindrically-shaped electrical connectors primarily for analog audio signals. Invented in the late 19th century for telephone switchboards, the phone connector remains in use for interfacing wired audio equipment, such as headphones, speakers, microphones, mixing consoles, and electronic musical instruments (e.g. electric guitars, keyboards, and effects units). A male connector (a plug), is mated into a female connector (a socket), though other terminology is used.

Plugs have 2 to 5 electrical contacts. The tip contact is indented with a groove. The sleeve contact is nearest the (conductive or insulated) handle. Contacts are insulated from each other by a band of non-conductive material. Between the tip and sleeve are 0 to 3 ring contacts. Since phone connectors have many uses, it is common to simply name the connector according to its number of rings: