What is PSTN? (Public Switched Telephone Network)

Do you want to know the basics of a PSTN? There are several key points you should know if you’re going to use it for your business. From the fundamental setups to new alternatives, here are a few things that you will want to know about PSTN.

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PSTN in Simple Terms

PSTN is short for Public Switched Telephone Network. You might know it as the traditional type of a circuit-switched telephone network. Since the 1880s, this type of system has been connecting callers from across the globe.

By using copper wires, mainly planted underground, the system provides businesses and households with a reliable way to communicate. This traditional system has several names, such as fixed-line telephones, landlines, or Plain Old Telephone Service (POTS). While these phone systems have been a reliable form of communication, they have been steadily declining over the past decade in favor of more digital technologies.

Currently, there are only 915 million PSTNs in the world—the lowest number in the modern century. If you want to learn about the future of communications, keep reading.

How Do PSTN Phone Lines Work?

There are a variety of components that help connect calls on a PSTN, including fiber optic cables, switching centers, telephone lines, cellular networks, cables, and satellites.

When you dial a number, the call moves through these networks to connect to your intended destination. First, the telephone converts the sound waves into an electric signal. That signal is transmitted to a terminal through a copper cable. The terminals collect the electrical signal and send them to a central location or office. This office routes the call (or electrical signal) through a fiber cable. From there, the fiber optic cable takes the signs, converts them into light pulses, and moves them towards the final destination.

While this process sounds complicated, it only takes a few seconds for you to reach the final location.

The Art of Switching

In a PSTN, it is all about switching, which is the backbone of a traditional telephone network. When you make a call, those stitches work to create a wire circuit between the two telephones. This connection remains for the entire duration of the call. There are four types of switching used in PSTN. Let’s take a closer look at them.

1. The Local Exchange

One or more changes can make up the local exchange. These exchanges connect those subscribers in a PSTN line. In some cases, these switches are known as the central office or switch exchange.

These spots can handle up to 10,000 telephone lines. Every telephone in a specific area is connected to the local exchange. Within the exchange, the number is identified, and the call is routed toward the right destination. If you look at the first three digits, those numbers represent the exchange. The last four digits identify the individual subscriber number.

2. Tandem Office

This exchange is also known as the junction network. Within this office, it contains several local exchanges and the management of switches between the local exchanges.

If you dial a number from the same city, the call could be routed to a tandem office from the local exchange, which will route the call to an office closer to the final destination.

3. Toll Office

When you make a national long-distance call, there needs to be additional switching. The toll office is connected to all of those tandem offices. For example, if you want to call another city, you will dial the number. That call will be switched from a toll office.

4. International Gateway

As the name suggests, these international gateways help manage global call switching and routing for domestic calls.

Are There Alternatives to PSTN?

With a Plain Old Telephone Service, these systems are not a great fit for many businesses and can be costly in the future. Plus, this switching technology has not made significant changes since the last century.

There are plenty of alternatives on the market, including VoIP. Voice Over Internet Protocol (VoIP) is one of the best alternatives to a PSTN system. VoIP transmits voice and other data over an internet protocol network. These telephones are connected to a cable modem or DSL, allowing you to connect to the internet.

What Is VoIP?

VoIP is also called broadband telephony, IP telephony, or internet telephony. No matter the name, they all do the same thing by transmitting voice through the internet. Your voice is converted into a digital signal as it travels over the internet to your destination.

Unlike PSTN, VoIP does not need a cable wire, and there is no exchange to make a call. With VoIP, it can handle all types of data transfers and calls. VoIP phone systems use packet switching to send and receive data when needed.

There is no need for a constant connection for the duration of the call. Along with that, VoIP does not require a dedicated line. The data packets use the internet and a router. Every data packet travels through the shortest and least congested path for a connection.

As you dial a number from a VoIP phone, the voice signal is converted into a digital signal with help from an IP phone. All that digital data is sent to a router, and it will be sent to a packet that is closest to the recipient.

Packet switching is cost-effective and efficient. Many businesses use VoIP systems. Companies use VoIP due to the boost to their productivity and cost savings.


While the PSTN phone system has been the workhorse for several decades, that technology is dated, and it just doesn’t align with the modern needs of businesses. For businesses, there are alternatives on the market, such as cloud-based solutions. With that, your business will see a reduction in costs and enjoy a more efficient phone system.

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