The Public Switched Telephone Network (PSTN) is a fundamental part of the history of telecommunications, serving as the backbone for voice communication for many decades. PSTN primarily relies on circuit-switching technology. This means that it establishes a dedicated communication channel between the callers for the duration of their conversation. 

This dedicated channel ensures reliable and high-quality voice transmission, with both parties having an exclusive line to communicate. This is in contrast to packet-switching technology used in modern IP-based networks, where data is broken into packets and sent independently to its destination.

PSTN is reliable and resilient and PSTN networks are designed to provide consistent service quality, even during adverse conditions like power outages. The network is structured to receive power from central offices, which are equipped with backup generators to maintain service during power failures. 

In its early days, PSTN was predominantly analog, with voice signals converted into electrical signals for transmission over copper wires. Over time, digital technology was integrated into the network, allowing for more efficient and clearer voice transmission. This digital transformation paved the way for various additional services like caller ID and call waiting.

While PSTN has played a central role in the history of telecommunications, it is gradually being switched off in favour of digital and IP-based technologies like Voice over Internet Protocol (VoIP) and broadband internet. These technologies offer cost-effective and feature-rich communication solutions, making them more popular for modern voice communication.