The PSTN, or Public Switched Telephone Network, is the traditional circuit-switched telephone network that has been used for over 120 years. It’s what your landline uses in the event you still use a landline…or know what one is (in the event you’re under 25 years of age).

The PSTN combines worldwide telephone networks, but, while many only think and visualize copper wires strung across telephone poles when they hear PSTN, it also includes fiber optic cables, LEC central offices, cellular networks, cable systems, and satellites.

The PSTN was created because initially calls could only be made between 2 telephones (think 2 cans connected by a string)―not too efficient. However, If you wanted to call somebody else, you would have needed a separate “string” stretched between you and them―also not a great option. This need to be able to connect to others gave rise to switching, which had to be manually done by local operator. Sure, that still sounds inefficient, but, in the day, it was a tremendous advancement. It’s actually what a PBX does, but we’ll get to that on another day.