PSTN:The Foundation of Traditional Telephony and Its Evolution in Modern Communication Networks

  PSTN(Public Switched Telephone Network)refers to the traditional fixed-line telephone network built and operated by telecommunications carriers.It is one of the infrastructures connecting telephone facilities and users worldwide.Below is a detailed explanation of PSTN:

  Components

  PSTN comprises various parts,including telephone lines,switches,transmission equipment,and other auxiliary devices.Specifically:

  Switches:Computer systems that process user calls and provide circuit-switching services.

  Transmission Equipment:Used for information transmission at the physical level,such as optical fiber cables and copper wires.

  Telephone Terminals(Mobile/Landline):User devices that provide voice input and output.

  Auxiliary Devices:Such as voice mailboxes and call waiting services.

  Working Principle

  PSTN operates based on circuit switching,connecting voice information from different terminals to enable calls between two or more users.This switching is based on analog circuit technology,meaning a dedicated circuit is reserved for the users during a call.

  Access Methods

  In the PSTN,users can access the network through various methods:

  PSTN Fixed-line Telephones:Connected to the telephone company's switch through landlines.

  Mobile Telephones:Access the mobile network through base stations.

  VoIP Telephones:Connected to the VoIP service provider's server using the internet.

  Historical Background and Development

  PSTN originated in the era when Alexander Graham Bell invented the telephone and is a collection of circuit-switched telephone networks.Although modern PSTN has achieved digitization in technology,its core remains a circuit-switched network based on analog technology.With continuous technological advancements,PSTN has undergone upgrades and transformations,transitioning from analog circuits to digital and IP technologies and incorporating many new features and services,such as call forwarding,conference calls,SMS,and ringback tones.

  Applications and Advantages

  PSTN plays a crucial role in the long-distance infrastructure of the internet.Internet service providers(ISPs)need to pay equipment owners to use PSTN's long-distance infrastructure,allowing internet users to only pay ISP fees.PSTN is mainly used for connections between remote endpoints and local LANs,as well as remote user dial-up internet access.Despite its slower data transmission speeds and lower resource utilization,PSTN offers relatively low communication costs,making it advantageous in certain application scenarios.

  In summary,PSTN is a traditional telephone communication system that remains an important infrastructure globally,particularly in emergency rescue and communication scenarios,despite the prevalence of mobile communications and the internet.