Overview step-by-step telephone switch

A stepping telephone switch is an automatic telephone switch composed of selector and relay. It uses mechanical actions to replace the wiring actions of the telephone switch operator. When a user calls a dial-up, the selector in the switch changes the connection position step by step as the pulse current is triggered during the dial-up, and the telephone line between the caller and the called user is automatically connected.

Brief history

In 1889, American A. B. Shi Duan Qiao invented the Three-magnet climbing rotary selector, a key component of the stepping telephone switch. In 1892, the first stochon-step telephone Bureau was put into use. In 1909, the German Siemens company made improvements to the step-by-step telephone switch of Shi Duan Qiao. It mainly changed the Three-magnet climbing and rotating selector to the two-magnet selector and made it into the Siemens step-by-step telephone switch. The UK has added a baton to stochon's step-by-step telephone switch, giving it the advantage of indirect control. In 1925, China installed Siemens step-by-step telephone switches in Tianjin and later installed shiduan Qiao step-by-step telephone switches in Qingdao and Nanjing. Since 1950s, Chinese production of JZB-1A type stepping telephone switch has been widely used.

Connection

The step-by-step telephone switch uses the selector to complete the call connection process. There are two types of selector: the rotating selector and the rising rotating selector. The simplest turn-on selector has an axis. There are 10 arcs around the axis, each of which contains 10 contacts. An arc brush is installed on the shaft, which can move up and down between the arcs of each layer, and rotate horizontally along the arc, connected to each contact. For example, when a caller calls number 25, the arc brush goes up two steps to the second-layer arc, and then rotates five steps to stop at the 25 contact, connect the caller with the call number of the 25 th user (called user.

 

In order to complete the connection call between users in a step-by-step telephone switch, multiple selectors are generally divided into several levels as needed to share the task of selecting the egress and user number. If the number of users is less than 100, only two dialing is required. Install a 100-line climbing transform selector (the selector is called the final adapter when used in this position), so that a user on 100 can call other users. However, each user's step-by-step telephone switch must have a dedicated terminal. To save the final connector and improve its utilization, you can set a small number of final connectors for all users to share, A rotating selector is added between each user's telephone and the final receiver, which is called the pre-selection device. When a user calls an offline call, the pre-selection device of the stepping telephone switch automatically rotates to find an idle Terminal Adapter. Then, the terminal adapter can be selected to the called user based on the user's dial number. When the number of users is greater than 100, but not more than 1000, three-digit dialing is required. Each user of 100 can be used as a group to add a level-1 selector, which is called a group selector. During a call, the step-by-step telephone switch selects the group where the called user is located, and then selects the called user from the group through the final adapter. Similarly, when the number of users exceeds 1000, but not more than 10000, the four-digit system is required. The first-level selector selects the thousands of digits Based on the grouping method, the second-level selector selects a hundred bits, and the final adapter selects the ten and one-bit numbers of the called users. Obviously, the first-level selector is added to the board for each additional dial-up.

Advantages and disadvantages:

The advantage of step-by-step telephone switch is that the circuit is simple, and each selector has its own route part and control part, which has a small impact when a fault occurs. Disadvantages: slow connection speed, easy wear and tear of machine keys, high noise, inflexible number arrangement, and low cost of online group utilization. Step-by-Step telephone switches do not provide roundabout relay performance, making it difficult to form an economic, secure, and flexible telephone network, especially a large-scale telephone network, it does not meet the needs of data, fax, and other communication services. Therefore, it is gradually replaced by a horizontal telephone switch and a storage program control electronic switch.