What is the PSTN (Public Switched Telephone Network)?

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The Public Switched Telephone Network (PSTN) is the global, interconnected network of traditional telephone systems that has historically provided voice communication services. Often referred to as landlines, fixed lines, or Plain Old Telephone Service (POTS), it forms the backbone of global telecommunications, connecting billions of telephones worldwide.

Key Characteristics of the PSTN:
Circuit-Switched Technology: This is a defining feature benin number database of the traditional PSTN. When a call is placed, a dedicated, continuous communication path (or circuit) is established between the caller and the recipient for the entire duration of the conversation. This circuit is reserved exclusively for that call and remains open until one party hangs up. This ensures consistent call quality and reliability, as the communication line is not shared with other users during the call. In contrast, modern internet-based communication (like VoIP) uses packet-switching, where data is broken into small packets and sent over shared pathways.

Physical Infrastructure: Historically, the PSTN primarily relied on a vast network of copper wires (known as "local loops") connecting individual homes and businesses to local switching centers. These local loops transmit analog voice signals. For longer distances, the network uses higher-capacity trunk lines composed of copper, fiber optics, and sometimes microwave transmission or satellite links.

Hierarchical Architecture: The PSTN is organized in a hierarchical structure of interconnected exchanges (also called central offices or switching centers):

Local Exchanges (Central Offices): These are the entry points for calls, connecting individual subscribers to the broader network. They handle call setup, routing, and termination within a local area.
Tandem Offices: These connect multiple local exchanges within a region, enabling efficient routing of calls that need to be transferred between local exchanges but don't require long-distance handling.
Toll Offices: These come into play for long-distance calls, connecting tandem offices and handling the routing of calls over longer distances, often between different regions or cities.
International Gateways: These specialized exchanges connect national PSTN networks to the global telecommunications infrastructure, allowing for international calls.
Reliability and Resilience: The PSTN is renowned for its high reliability and resilience, often boasting "five nines" (99.999%) operational time. This is partly due to its independent power sources at central offices, allowing it to function even during local power outages, which is a critical advantage for emergency services.

Voice-Centric Design: The PSTN was designed specifically for voice transmission. While it has evolved to incorporate digital technologies in its core network (converting analog voice signals to digital for efficient transmission over fiber optic cables), its primary purpose remains voice communication. Its bandwidth is limited compared to modern digital networks, making it unsuitable for high-bandwidth applications like video conferencing or large data transfers.

Global Connectivity: Through the interconnectedness of national PSTN networks and adherence to international standards like E.164 (the global numbering plan), the PSTN enables communication between nearly any telephone worldwide.