What is PSTN, and How does it work?- A Complete Guide

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For centuries, PSTN has been connecting the world. Even though we have newer technologies now, many offices still use PSTN phones. The reason is simple - it’s reliable and does the job very well.

So, what is PSTN, and how does it work? In this article, we’ll explore it in detail. Keep connected.

What is PSTN?

PSTN stands for Public Switched Telephone Network. It is the traditional system for making telephone calls and uses a network of cables and telephone lines to connect calls between people.

When you make a phone call, PSTN phone lines help your voice travel from your phone to the person you're calling. It's like a big web of wires that connects you and your desired person to communicate smoothly. It allows you to converse with someone far away, as if they're right next to you.

How does PSTN work in 2024?

PSTN network in 2023 still works much like it always has but with some modern updates. The basic idea is the same - it converts your voice into an electronic signal when you communicate through the phone lines.

The PSTN phone calls work begins right from your phone. You could use a landline or a mobile phone. If it's from a landline, the call goes through wires. If it's a mobile call, it first travels to a nearby cell tower and aids the connection.

Today, PSTN uses a mix of old and new technologies. It still has the traditional copper telephone lines, but now it also includes fiber-optic cables and digital technologies. This mix only helps to make the PSTN phone line more advanced. It significantly improves the speed of connection and your voice clarity.

Public Switch Telephone Network uses switching centers and multiple touchpoints to route your call. These centers are like crossroads that direct your call to the right path. It ensures it connects you to the right recipient. The whole process happens in just a few seconds.

Even if it includes the complex use of technologies, for you, it's a very simple process to use the system. All you need to do is - dial a number and wait for someone to pick up on the other line.

PSTN Network Architecture

As we discussed above, PSTN, a Public Switched Network, involves switching centers and multiple touchpoints to route phone calls. Your call passes through several key elements of the network before reaching its destination. Let's explore these components:

Local Exchange Carriers (LECs)

Local Exchange Carriers are the initial touchpoints in the PSTN network. It comes into play when you make phone calls within a specific geographical area. Let’s say you’re making a local phone call. As you dial the number, it first connects to your local LEC, which then determines the best route for your call.

Tandem Office

A Tandem Office is an intermediary between local exchange carriers and long-distance networks. It steps in when you make a call outside the local area. For instance, you’re trying to connect to another geographical region rather than a local one. In such a scenario, it routes your calls to the appropriate network to aid communication in wider area coverage.

Toll Office

The Toll Office also takes over for longer-distance calls. It's responsible for routing and managing calls that travel over larger geographical areas, often between cities or regions. When you dial a long-distance number, the toll office directs your call through the most efficient path to its destination.

International Gateway

When you need to cross a national border with your call, then the international gateway is your transportation mode through PSTN phone lines. The international gateway is what manages the routing of your international calls. It aids in smooth telephonic communication between different nations.

Carrier Access Points

Carrier Access Points are like checkpoints within the network. Imagine you’re trying to have important interactions on phone calls but are facing an issue due to an overcrowded network. Frustrating, right? This is where Carrier Access Points comes to the rescue. It manages the flow of the data and prevents network congestion to route your call efficiently.

Trunk Lines

Consider Trunk Lines as the highways of the PSTN. They connect the different components of the network, like local exchanges to tandem offices and tandem offices to toll offices. They carry a large volume of calls simultaneously. As such, it ensures a smooth and continuous flow of your communication.

Customer Premises Equipment (CPE)

Customer premises equipment is your beginning point and destination point for phone calls through the PSTN line. Customer Premises Equipment is the device you use to make and pick up calls at homes or offices. Your call starts and ends with CPE.

How Much Does PSTN Phone Line Cost?

So, various touchpoints in the PSTN network architecture facilitate seamless phone connections to reach your desired recipient. But how much does it cost to connect to your desired recipient through PSTN? Well, it depends on several factors, whether you’re using it for personal or business use. Plus, the type of equipment you use also affects your cost.

Cost of PSTN for Consumers

If you’re looking to set up a PSTN network in your home, you would need to install phone lines and purchase a telephone if you already don’t have one. Typically, you’ll pay $50 to $200 for installation. Additionally, you would also need to spend on monthly service fees. The PSTN services are generally available with a basic monthly fee for local calls and additional charges for long-distance or international calls.

Cost of PSTN for Businesses

You can expect the PSTN network to be more costly when you are installing it for your business. This is because a business PSTN line often involves multiple phone lines and needs a more robust infrastructure.

Due to the higher costs, many businesses are switching to VoIP services. The VoIP service providers like Calilio offer business communication plans at an affordable price.

Cost of PSTN for PBX System

A traditional PBX, also known as on-premise PBX, uses PSTN lines to connect the calls. To employ a PBX system with PSTN, you need to spend on installation, maintenance, and call charges. The cost here depends on the scale of the PBX system and the extent of PSTN integration. Larger companies with more extensive communication needs might face higher costs due to the number of lines and the complexity of the setup.

Benefits of Public Switched Telephone Network

The Public Switched Telephone Network (PSTN) continues to be widely used for personal, business, and PBX (Private Branch Exchange) applications. So, why is it so popular despite being an older technology? The answer lies in the extensive benefits it offers. Here are some key benefits of the PSTN telephone network.


PSTN operates through a network of physical cables and lines. It often remains operational even in adverse conditions like severe weather or power cuts. Isn’t it impressive? We know it is. Such network reliability is crucial, especially in emergency situations where a consistent communication line is a must.


When it comes to security, PSTN offers a level of protection that is hard to match. Since PSTN network architecture is largely physical, it’s less vulnerable to hacking and eavesdropping. Worry about sensitive conversation leaks? Well, with PSTN, you don’t have to be. The dedicated lines and traditional data transmission methods used in PSTN protect your data and interaction well.


The usability of PSTN lies in its simplicity. It’s easy to use and doesn’t include complex setup procedures. Even if you’re not tech-savvy, you shouldn’t find it hard to understand the setup and make the call. Additionally, unlike many other new phone systems, it doesn’t require specialized knowledge to maintain your system.

Emergency Services

One of the critical roles of PSTN is in emergency services. We all know how invaluable it is to provide accurate caller locations for emergency response teams. PSTN can provide precise location data, which can be crucial in emergency situations where every second counts. It ensures quick response times and efficient assistance.

Quality of Service (QoS)

Quality of service matters whether you’re using a communication system for personal or business use. In the business context, PSTN’s high-quality voice communication helps you to maintain professionalism and effective collaboration. For personal use, you get to experience clear and disruption-free communication. You’ll love it when connecting with loved ones or during important collaborations.

Drawbacks of PSTN Phone/POTS

Now, we know the Public Switched Telephone Network (PSTN) offers many impressive perks. But, before deciding to implement it, it’s also important to explore its drawbacks. Yes, the reliable PSTN network has some drawbacks, too. Let’s explore them one by one.

Limited Calls

If your business environment involves handling multiple calls, then the PSTN telephone network may not be the solution for your business communication. This is because PSTN lines are dedicated to single calls. It means each line can only manage one call at a time. So, employing it can be ineffective for handling high call volumes.

Limited Features

While PSTN covers the basics like call waiting, caller ID, and voicemail, it lacks advanced functionalities like video calling, file sharing, and integrated messaging. This limitation can be problematic if your business needs more than just voice communication.

Lack of Flexibility

As we know, the modern business landscape rapidly keeps changing. You may want to add or remove the phone lines to your business at any time. Unfortunately, it’s not easy with the PSTN phone system.

Slow Transmission

Compared to modern digital communication methods, PSTN tends to have slower transmission rates. You may occasionally experience latency and delay when making international calls. It can affect communication efficiency, especially in scenarios where quick information exchange is crucial.

Alternatives of PSTN

If the above drawbacks concern you, you can consider other options for your communication needs. Luckily, there are many alternatives to PSTN, each with its advantages. Let’s compare these PSTN alternatives.

PSTN vs Hosted PBX

Hosted PBX (Private Branch Exchange) is a modern telephone network solution for businesses. Unlike traditional PBX systems that require physical hardware on-premises, Hosted PBX operates on the Internet. You can not only get rid of the unappealing wires lying here and there, but it comes with a range of advanced communication features. Voicemail-to-email, call forwarding, and conference calling are to name a few.

Here is how Hosted PBX compares to PSTN:



Hosted PBX


Physical Lines






Basic features for phone calls

Extensive business communication features


Fixed Setup

Highly Customizable


ISDN(Integrated Services Digital Network) is a telecommunications standard that enables the digital transmission of voice and data over traditional PSTN networks. Opt for this option if you already have a PSTN network but are looking to increase data transmission speed with added voice clarity.

Here is how ISDN compares to PSTN:  







Data Speed



Voice Quality



Network Configuration


More complex but versatile


VoIP (Voice over Internet Protocol) is a technology that allows voice communication over the Internet. We can say VoIP is the most advanced, feature-rich, and reliable communication solution compared to PSTN phone lines and its other alternatives. Though its more of a business communication solution, you can use also use it for personal use.

Here is how VoIP compares to PSTN:








Basic features for phone calls

Extensive business communication features


Fixed location

Accessible from anywhere with an internet connection


Typically Higher


History of Public Switched Telephone Network

Looking back at the history, PSTN started in the late 1800s. It all started with Alexander Graham Bell's invention of the telephone in 1876. Initially, operators were there to connect the calls between the two parties manually. This changed in the early 20th century with the introduction of automated telephone exchanges. It not only replaced manual operators with mechanical systems but also facilitated connecting calls more efficiently.

As time went by, the network further evolved with the transition from analog to digital technology. This transition significantly improved the capacity and quality of calls. Later on, fiber-optic cables were introduced with the aim of further improving the call quality. And it worked well. Those fiber-optic cables provided even higher bandwidth and clarity. Today, you can experience unparalleled voice-quality conversing through the PSTN network.

Switch from PSTN to VoIP with Calilio

With reliable and straightforward functionality, the Public Switched Telephone Network (PSTN) has impressively served countless users. However, its popularity has gradually declined in recent years as we see more and more advanced communication tools coming through. One particular tool that impressed me most is VoIP (Voice over Internet Protocol). VoIP technology offers several advantages over PSTN, including lower costs, higher flexibility, and a broader range of features.

That being said, choosing the right VoIP service provider is equally important to ensure maximum features in your communication tool. Consider switching Calilio from PSTN to VoIP. Our service not only includes all the capabilities of traditional PSTN, but it comes with highly customizable VoIP features. You can tailor your communication tool all by yourself. Contact Us today.

Frequently Asked Questions

What does PSTN stand for?

PSTN stands for Public Switched Telephone Network. This traditional phone system used worldwide consists of a network of cables, telephone lines, and satellites.

Is PSTN analog or digital?

PSTN was originally analog, and traditional lines use analog technology. However, later on, it has evolved to include digital elements. Today, the PSTN network also incorporates digital technology.

What’s the difference between Direct Inward Dialing (DID) and PSTN?

Direct Inward Dialing (DID) refers to a feature of telephone systems that allows you to dial an extension directly without an operator. DID works within a PSTN or VoIP system. On the contrary, PSTN is the overall network for telephone communication.

What is PSTN gateway?

A PSTN gateway is a device that connects a PSTN line with other networks, such as a VoIP network. It allows different types of communication systems to work together.

Why is VoIP better than PSTN?

VoIP offers all the important capabilities of traditional PSTN with added features, including video calling, text messaging, and flexibility in usage. Moreover, it is more affordable than PSTN.

Is PSTN the same as a landline?

PSTN is often synonymous with a landline. It refers to the traditional wired phone system that connects calls through a network of cables.

Does PSTN still exist?

PSTN still exists today and is widely used, especially for landline telephones. Despite the rise of digital communication, it still remains a key part of global telephony.

What is replacing PSTN?

VoIP (Voice over Internet Protocol) and mobile cellular networks are progressively replacing PSTN. These technologies offer more features and flexibility compared to traditional PSTN.

Does VoIP use PSTN?

VoIP can use PSTN as a backup or for connecting to users who are on the PSTN. However, VoIP primarily relies on internet connectivity for call transmission.

Can you dial PSTN to SIP?

You can certainly dial from PSTN to SIP (Session Initiation Protocol used in VoIP systems). A network gateway that connects PSTN and VoIP networks makes it possible.

Do cell phones use PSTN?

Cell phones primarily use cellular networks, which are different from PSTN. However, they can connect to PSTN through cellular network stations.

What is the difference between PSTN and cellular?

PSTN is a wired network for landline phones, while cellular networks are wireless and used for mobile phones. Cellular networks offer more mobility compared to PSTN.

What is a PSTN dialer?

A PSTN dialer is a device or software that automates phone calls over the PSTN. It's commonly used in telemarketing and customer service.

What are the disadvantages of PSTN?

Compared to modern digital communication tools, we can identify many drawbacks of PSTN. The key ones include limited features, lack of flexibility, and slow transmission rate.