It's the traditional form of telecommunication, providing voice communication services globally. 

• Analog and Digital Technology: The PSTN initially used analog technology for voice communication but has evolved to include digital technology as well. This includes the use of digital signaling networks and fiber optic cables in addition to copper wires.

• Circuit Switching: A defining characteristic of PSTN is circuit switching, where a dedicated communication path is established between two points for the duration of a call.

• Telephone Numbers: PSTN uses a standardized system of telephone numbers, which includes country codes, area codes, and individual phone numbers for routing calls to their destinations.

• Global Network: The PSTN is a global network, connecting telephones all around the world. It includes undersea cables, satellite links, and an extensive network of wiring and infrastructure on land.

• Voice Quality: Traditionally, PSTN has been known for high voice quality and reliability, though this can vary based on the condition of physical lines and network infrastructure.

• Landline Telephones: The most common use of PSTN is for landline telephones, which have been the primary method of voice communication for over a century.

The PSTN has been the backbone of global telecommunications for many decades and continues to play a significant role, particularly in areas where newer digital communication technologies are not yet fully implemented.