Introduction to the PSTN (Public switched telephone network, common switched telephone network)

1. Introduction

The Public Switched telephone network (switched telephone network or PSTN) is a circuit-switched network for global voice communications, the largest network in the world, with a population of about 800 million.
The public switched telephone network was first established by the telephone invented by Bell in 1876. The PSTN has gone through the phase of magnet exchange, air separation, program-controlled exchange, digital exchange and so on, it is almost all digitized network, according to function attribute is divided into end bureau, long-distance Telephone Center Bureau, Main Center Bureau, and International Telephone exchange Center.
The public switched telephone network mainly consists of two parts, the switching system and the transmission system, in which the equipment in the switching system is mainly the telephone switchboard, and the telephone exchange has experienced the magnet, step and crossbar switches with the development of the electronic technology, and finally to the development process of the SPC Exchange. Transmission system is mainly composed of transmission equipment and cables, transmission equipment developed from the early carrier multiplexing equipment to SDH, cable also developed from copper wire to optical fiber.
In order to adapt to the development of the business, PSTN is now in the transition period of satisfying the transmission demand of voice, data, image and so on, it is developing towards NGN (Next Generation Network), moving and fixed fusion.
The technical standards used in the PSTN are addressed by the International Telecommunication Union (ITU), using e.163/e.164 (popularly known as telephone numbers).

2, Distance

According to the PSTN transmission distance, generally can be divided into five levels:
Class 1 (Regional center)
The Class 1 office was the regional Center (RC).
Class 2 (Sectional center)
The Class 2 office was the sectional Center (SC).
Class 3 (Primary center)
Class 3 is the main Center bureau (Primary Center, PC, for short)
Class 4 (Toll center)
Class 4 Telephone switch
Class 4 is a long-distance call center Bureau (Toll Center, referred to as TC),
Class 5 (Local exchange)
Class 5 Telephone Switches
Class 5 is a zone Exchange (local Exchange) or a call terminal (end Office, referred to as EO).
International Overseas Call Centers

References: Baidu Encyclopedia and Wikipedia