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What Is the Public Switched Telephone Network (PSTN)?

by Margaret Joy

The sun may be setting on the PSTN, but it's still worth knowing what it is and how it works!

The PSTN (public switched telephone network) has many names. You might see “POTS” (plain old telephone service) or just a simple “landline.” So what is the PSTN exactly? Read on to find out. 

What Is the PSTN?

It’s a bird! It’s a plane! It’s a…mess of ancient and expensive copper wiring. We all know the system patented by Alexander Graham Bell. (Shoutout to Elisha Gray who actually developed a telephone system months earlier but missed out on the patent by a measly two hours.) Despite the simple nicknames, the PSTN network involves more than just telephone poles and your grandparents’ house phone.Towers, switching centers, satellites, cable, and yes, even cellular networks are all part of POTS. Don’t forget the trans-oceanic cables, either! All of these combined create the circuit-switched telephone networks we’ve known since the 19th century.

We go into more detail in our comprehensive What is VoIP blog, but here’s the gist: Circuit switching sends voice signals across wires. Back in the days of switchboard operators, the copper wire connecting two people on a call was for that call only. Think of dial-up Internet days when you could be on the phone or on the Web, but not both at once.

Diagram showing how circuit switching works.
The PSTN works through circuit switching.

Are Landlines Obsolete?

The PSTN is a physical worldwide network, which deserves a moment of awe. But it’s also ancient by modern technology standards, so the global choice to phase out the PSTN might not seem so strange. The process started several years ago, and like any global project, it will continue for many more years. It makes sense, considering most of us switched from analog to digital in many aspects of our lives in the past decade. And that’s essentially what the PSTN is: analog. With its copper wiring and large-scale infrastructure needs, landlines have become more outdated with every passing day. VoIP, developed for public use in the 1990s, is slowly replacing POTS across the world. 


As wireless technology spread, so has VoIP adoption. With reliable Internet connections in the majority of populated areas, the bulky, pricey, and time-consuming POTS has become more obsolete. It’s still incredibly useful—not to mention widespread, geographically speaking—for most of us and necessary for rural areas that aren’t yet on 3G. But with bulky infrastructure comes bulky setup, and businesses continue to choose VoIP instead for its lower cost, flexibility, and remote-friendly installation.

Photo of an old lab using corded landline phones.
If the technology looks like it belongs in the previous century, it’s time for an upgrade.

By now, there’s really only one major item in the pros column for landlines: power. As we’ve discussed in our VoIP Advantages and Disadvantages Versus the PSTN blog, landlines run on separate power than the rest of your building. And because VoIP relies on Internet access, you’re out of luck if the power goes out. However, that’s only a short window of superiority; if the phone company loses power too, a landline user can rely on the backup battery system. But considering the world has chosen to phase out the PSTN rather than update its infrastructure, we’re willing to bet some of those backup systems haven’t been checked in a while. 

For a full rundown on the extensive pros in VoIP’s favor, we recommend reading the blog we just mentioned. But here are the CliffsNotes to speed you on your way:

  • Call Quality: VoIP has better call quality than the PSTN does. How? Codecs. If you know, you know; if you don’t, we explain why VoIP offers the best call quality.
  • UCaaS: Everybody wants streamlined communications at work. You can’t get that with analog technology, but you can with cloud VoIP. 
  • Portability: When you unexpectedly switch to working from home, you can’t take your POTS desk phone because it’s wired into the network. With VoIP, you can take your phone if you like the hardware, or you can answer calls from a softphone on any device. 
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