Development
Progress in telephone exchange technology has experienced four major phases of manual exchange, electromechanical exchange, electronic exchange and program-controlled digital exchange.
Artificial exchange is a switching method that manually completes the call two sides of the call through the telephone exchanger. The user phone is divided into two types of magnets and co-electricity, and the magnet phone requires a user to bring a dry battery, and the telephone is uniformly powered by the switch. Each subscriber line is provided with a plug hole (fixed) and a plug rope with a plug (which can be elongated). When a user is called as a call, the operator tells the call number or name, and the attendant pulls the caller of the calling user out of the plug hole to the other party, and call the other party to complete the call. When a user is called as a called called, the caller of the calling party will be inserted by the attendant to the hex, complete the connection between the two parties. The artificial switch has appeared earliest in 1878, because it is a person who has no control as a switching action, therefore the adoption efficiency is low, the speed is slow, and the labor intensity is a most original switching method.
Electromechanical exchange is an automatic switching manner that uses electromagnetic mechanical action to control both part of the call. In 1891, American Almond B · Historical Joe was "step-to-instance automatic telephone terminal". In 1892, "Step-Automatic Telephone Switch" made in this kind of junction was officially put into use. Step-by-step telephone switches rely on the dial-up pulse of the user phone to directly control the mechanical relay to climb and rotate the terminal of the terminal to complete the connection of the line contacts. This mechanical exchange method is much wear, low service life, large noise, but it achieved mechanical operations.
In 1919, the Swedish Palm Glen and Betalan invented the "vertical and horizontal junction". The vertical switch produced by the vertical trip is first put into use in Sweden in 1926. The vertical and horizontal switch relies on the user dialing, and the active control of the terminal is indirectly controlled by a public control device (the junction and the marker). The functionality of this public control device is similar to the operator in manual exchange, responsible for receiving the user's dialing and stores, count, forwarding and other work. In comparative exchange, the mechanical action of the vertical switch has a lot of mechanical actions, and it is made of wear-resistant precious metal, so the operation noise is small, the wear and mechanical maintenance work is also small, and the work life is also greatly extended.
After the 1940s, with the development of semiconductor electronic technology, the telephone switch has begun to gradually switch to the electronic control phase to the electronic control phase by the electromechanical exchange stage. The logic control portion of the switch is easier to implement the semiconductor device, so it is first replaced by the electronic components. However, the line continues is limited by the technical level at the time, and it is difficult to find an electronic switch that can be smaller than the mechanical metal contacts and lower costs. Although the wiring speed occurs after the wiring speed can be similar to the electronic components, it is still a semi-electron or quasi-electronic switch.
1965, the first program-controlled switch NO.1, which was successfully developed by Bell, USA. This is the first telephone exchange system implemented by the storage program control technology. However, the system is transmitted is an analog speech signal, and the connection portion of the line is still a space switching method. The split transmission refers to the lines of the two sides of the call until the call is completed, and the line is always in a physical turn-on state. After the call is completed, it is also physically demolished, restores the original state.
1970, Ranon, France opened the first priorcted digital telephone exchange E-10. The control portion is done directly by the computer, while the continuous portion completely implements the time division exchange of the PCM digital voice encoded signal.
After entering the 1980s, the program-controlled digital telephone switch gradually spread in the world, and became the mainstream of telephone exchange communication system. Today, the program-controlled digital telephone exchange network has developed into a comprehensive business digital network that supports non-talk business, accompanied by the progress of computer network technology and dedicated integrated circuits, gradually integrating with packet switched networks, forming high reliability and flexibility. Digital communication network. A switch network with soft exchange features is the core concept of next-generation network (NGN) and gradually be accepted by more and more customers and operators.
Basic Principle
Communication is information exchange and delivery between people through a certain medium. In general, regardless of the method, what medium is used, as long as information is transmitted from one place to another, it can be referred to as communication. When the transmission medium is electrical signal, it is called electrical communication, referred to as "telecom".
AD 968, my country invented a thing called "bamboo letter", which consists of two small bamboo tubes and rope connecting them. Use bamboo tubes, one side can hear the other side whisper. Bamboo is considered to be the prototype of the phone. In the 1930s, people began to explore the use of electromagnetic phenomena to transmit music and voice. In 1876, American Bell invented the phone. In 1877, the first telephone lines set up in Boston communicated with Mr. Charles Williams, and his private residential in Somerville. In the same year, some people sent news news to the "Boston Global News", and started the public using the phone.
The most basic principle of telephone communication is that each user uses a telephone, connects the phone with a wire, and converts the two locations to each other. If the triplet is paired with him, you need to connect them separately with three pairs. In this kind of push, if an IV telephone is required, the N (N-1) / 2 pair of connectors can be arbitrarily called between N-telephone.
It is not difficult to see that when the phone is a lot, the number of connectors required is very large. This not only reduces the network line utilization, increasing construction investment, but also difficult to do with a large number of connectors in actual engineering installation. At this point, a public device can be installed at the user distribution intensive center, and when arbitrarily calls, it is implemented by the public device. The line is removed after the call is completed to use other users. This public device is a telephone switch.
Function Model
Phone Exchange Man Dirents Connect between any two users, for this purpose, the switch generally needs to have the following function:
(1) Timely discover the user's access request.
(2) According to the user dial, control, establish and remove the main, the subject between the calls.
(3) Supports multi-user simultaneously and does not interfere with
(4) to provide different exchange services, such as transfer calls, exhalation restrictions, depending on the user's different business needs.
The call type that can be controlled includes: this Council call, outgoing call, incoming call, and transfer call. The call of this Council refers to the continuation between the users of this bureau; the outgoing call refers to the connection between the user and the relay; the incoming call is the connection between the relay and the user user; the transfer call refers to people relay and out Continue between continues.
According to the above functional requirements, the functional model of telephone exchange can be derived, in which the terminal interface module is connected to the external device, and the function is divided into two parts, part of the local user equipment, and the other Other switches are connected by a trunk. The connection function module is used to complete the connection path between any two users, and the control function module controls the establishment or demolition.