PSTNverkosta

PSTNverkosta refers to the Public Switched Telephone Network (PSTN), the traditional public voice telephony system. In Finnish discussions it denotes voice calls and related services that originate from or terminate in the PSTN. The PSTN is a circuit-switched network that historically used copper telephone lines to carry analog voice, later digitized and transported over digital transmission links. It forms the backbone of fixed-line telephony in many countries and historically supported fax, modem data, and dial-up connections.

The PSTN is organized in layers. Local access networks connect customer premises to local exchanges, typically Class 5 switches, via copper loops. Long-distance traffic travels through trunk networks and higher-order switches, such as Class 4. Signaling has evolved from in-band methods to out-of-band signaling, notably SS7, which enables call setup, routing, number translation, and billing across the network. Digital variants include ISDN services (BRI/PRI) that use the same general network with digital transmission.

Operation and services. A call is established through a dedicated circuit for its duration, providing predictable latency and quality for voice. The PSTN supports emergency calls, number portability, caller ID, and intercept/billing functions. It interconnects with mobile networks and with other public networks worldwide through interconnection agreements and gateways.

Modern context. Many regions are transitioning toward IP-based voice (VoIP) and mobile networks, often introducing gateways and SIP trunks to bridge PSTN and IP networks. Some operators plan phase-outs of legacy copper lines, while regulators emphasize universal service, reliability, and emergency access. In practice, PSTN remains a foundational and highly reliable component of national communications, even as convergence with IP technologies continues.