PSTN is a global network of analog and digital telephony systems used for transmitting voice signals over wired and wireless lines. It represents the traditional telephone infrastructure that enabled voice communication long before the emergence of IP telephony and mobile networks.
PSTN connects two users through a chain of circuit-switched connections, starting from the caller’s telephone, through local exchanges, trunk lines, and finally to the recipient’s device.
How PSTN Works
- A user dials a number, which is routed to the local telephone exchange.
- The system determines the optimal connection path via switches.
- A dedicated voice channel is established between the two endpoints for the duration of the call.
- Once the call ends, the connection is terminated, and the resources are released.
PSTN Infrastructure Includes:
- Analog telephones (traditional landlines);
- Digital lines (e.g., ISDN);
- Underground copper cables, fiber optics, and satellite links.
Why PSTN Is Still in Use
Despite the rise of IP telephony and mobile networks, PSTN remains relevant in:
- Government and banking institutions;
- Emergency communication systems;
- Remote and rural areas;
- As a reliable backup communication channel.
The Future of PSTN
Many countries are phasing out PSTN in favor of VoIP, SIP, and 4G/5G mobile networks. Telecommunications providers in several regions (e.g., the UK by the end of 2025) have already announced the planned decommissioning of PSTN systems.