Insights & Resources6 min read

Guide to the Public Switched Telephone Network (PSTN)

Learn how the Public Switched Telephone Service (PSTN) works, and why it may be on its way out.

Brian Segal
Image of older office phone
It's safe to say that the Public Switched Telephone Service (PSTN) forever changed the way we communicate. Instead of relying on letters to traverse the country or globe, we were connected to people in real time. But what exactly is the PSTN, and how does it work? Well, that's exactly what we're here to explain.

What is the PSTN?

PSTN (Public Switched Telephone Network) refers to the traditional backbone of telecommunication across the globe. While today’s communication network has seen a digital shift, the PSTN historically made use of underground copper wires and telephone lines to connect people and businesses.
Also known as the Plain Old Telephone Service (POTS), recent years have seen a decline in demand for PSTN lines. While some may question why we even have a PSTN as the world shifts to an IP Network, the transition will take both time and money. Meaning, the PSTN still remains a reliable means of communication.

How PSTN Lines Work

The concept of how the PSTN works isn’t as complicated as people might think. The implementation, on the other hand, is a completely different story.
Before diving into just how PSTN lines work, it’s important to first understand a few key terms. So, let’s define the main offices in play.
  • Central Office (CO): Also known as the local exchange, the central office is usually made up of one or more offices that connects subscribers to a PSTN line. The central office a subscriber is connected to will usually depend on their geographical location. The exchange then identifies the number being dialed, and routes it to the desired destination.
  • Tandem Office: Also known as a junction network, a tandem office is a step up from the local exchange. It serves a larger geographical area, and is made up of multiple local exchanges. The tandem office has the capability of routing calls between local exchanges.
  • Toll Office: When a number is dialed outside the geographical area of a local exchange or tandem office, it will be routed to a toll office. The toll office is where long distance, domestic calls can be made. Think of placing a call from California to New York.
  • International Gateway: As the name implies, the international gateway is used to route calls outside of the country. When a foreign number is dialed, the international gateway manages the call switching, and routes calls to the desired country.
With those few key terms in mind, let’s break down how PSTN lines actually work. Immediately after dialing a number, your phone works to convert sound waves, your voice, into electrical signals that can be transmitted to a terminal via cables. The electrical signals are then sent by the terminal to the central office, or local exchange.
Once the central office receives the electrical signals, they are routed to the correct destination through cables in the form of light pulses. Once the call reaches its destination, it is converted back to electrical signals, and routed to the correct terminal.
Finally, the terminal will route the call to the correct phone number. Once the phone receives the electrical signals, it will convert those signals back into sound waves. Which allows for nearly instantaneous communication between you and the person you are calling.

PSTN Pros and Cons

As mentioned earlier, the telecom is seeing a major shift from PSTN to internet based networks. In fact, 2019 saw the fewest fixed telephone line subscriptions this century. While Voice over Internet Protocol (VoIP) has a lot more to offer, there are still things to consider when deciding whether or not PSTN is right for your business.
Like any decision, we believe it’s important to break down the pros and cons of PSTN so you, the reader, can make the right choice.

Advantages of Using PSTN

  • Proven Reliability: It’s difficult to argue against the proven track record of PSTN lines. The Public Switched Telephone Service has been around for quite a while. So, it makes sense that the technology and infrastructure has been nearly perfected. What’s even better, is that even if there was a power outage, or your company internet goes down, your communication capabilities won’t be affected.
  • Better Security: Another area where PSTN shines is it’s security. Since PSTN mainly relies on analogue lines (or copper wire lines), it’s not nearly as susceptible to cyber attacks as it’s VoIP counterpart. Although, VoIP has come a long way as far as security is concerned.
  • Ease of Use: Often overlooked, PSTN lines offer an ease of use that can often get lost with modern communication solutions. From setup to communicating, the familiarity that comes with PSTN lines can make a world of difference when getting up and running.

Disadvantages of Using PSTN

  • More Expensive: One glaring issue that faces PSTN users is the heftier price tag that comes along with the traditional communication solution. When compared side by side with VoIP pricing, PSTN setup and calls prove to be much more expensive.
  • Fixed Phones: The nice thing about VoIP, is you’ll have access to your calls from just about anywhere with an internet connection. If you run a business that requires frequent customer connection, the use of PSTN lines may prove to be an issue. With fixed lines, your calls will be limited to the office, or wherever else your phone system may be set up.
  • No Versatility: Aside from cost, PSTN lines are quickly becoming outdated with their lack of feature options. With PSTN, your business will only have access to voice data. While that may be all you need today, VoIP has a lot more to offer in terms of call tracking, recording, analytics, and even video conferencing.

PSTN Alternatives

The PSTN has been around since the late 19th century. Since then, technology in the telecommunication space has seen a dramatic evolution to combat some of the limitations and expenses associated with the Plain Old Telephone Service.
Perhaps the most notable alternative to the PSTN is VoIP, which stands for Voice over Internet Protocol. Over the last decade, businesses have been making the switch from PSTN lines to VoIP, and for good reason. Let’s jump into some of the reasons you may want to consider making the switch for your business as well.

PSTN vs VoIP: How it Measures Up

For businesses, finding the right communication solution is of the utmost importance. Especially when you consider costs and limitations that can potentially hinder your business needs. If you’re considering whether or not PSTN or VoIP is the right solution for your business, here’s what you need to know.
  • Cost: When it comes to pricing, there’s no question that PSTN lines will end up costing your business more, and it’s not even close. Since VoIP uses existing internet connection to place and receive calls, you’ll end up saving a fortune.
  • Connectivity: There’s two things to consider when it comes to connectivity. When using PSTN lines, you’ll only be able to make and receive calls when you're in the office. That being said, you won’t have to worry about power outages, or slow internet speeds hurting call quality. On the other hand, VoIP allows you to connect with your customers from anywhere with an internet connection.
  • Capability: If you’re looking for incredible out of the box features, you're not going to find it with PSTN lines. Unfortunately, going with PSTN, you’ll be limited to strictly voice data. Meaning, you won’t be able to include video conferencing, call recordings, and more like you would with VoIP.
  • Security: While there were early concerns about security with VoIP, making a call over the internet today is both safe and secure. PSTN lines aren’t as susceptible to cyber attacks due to their physical nature, but security won’t be an issue with whatever option you choose to go with.
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