PSTN Calling 101 - Fundamentals & Benefits

Learn about PSTN calling, its advantages, and how it works. Improve your understanding of telephony systems.

PSTN Calling 101 - Fundamentals & Benefits
PSTN Calling 101 - Fundamentals & Benefits

What is a PSTN Calling?

PSTN is the circuit relay telephone network used worldwide. It is no longer a fixed analog telephone network, but today it is almost digital and includes mobile telephone lines as well as fixed telephones. These networks provide infrastructure and services for public telecommunications.

The PSTN calling platform has been a tool to communicate with businesses, households, and anyone from generation to generation. These are the good old rocker switch phones that existed in the last century. PSTN Calling was formerly used to connect to houses and business phone calls. According to an article conducted by the National Interest Organization, in 2004 approximately 90% of US households had a working landline (PSTN) phone. Today that number has dropped to 40%. Although it has decreased, some people still use PTSN Calling. This article will look at many features such as what PTSN Calling means and how it works and its history. And we will also look at the differences between VOIP and PSTN calling’s benefits.

How does PSTN work?

PSTN allows its users to make landline phone calls. It consists of switches on a network that act as nodes to enable communication between two points in the network. These switches are located at central points. A call is made after routing through multiple switches. A PSTN telephone line is used with traditional dial-up modems to connect a computer to the Internet.

This method used to be used for the Internet, but this changed with the introduction of broadband Internet services. We can say it is a combination of telephone networks used worldwide. When a call is made, a wire loop is formed between the two phones and lasts for the duration of the call. For clarity, let’s explain this process step by step.

  • Step 1 – First, your telephone set converts sound waves into electrical signals. These signals are transmitted to a terminal via a cable.
  • Step 2 – The terminal collects electrical signals. It then forwards them to the central office (CO).
  • Step 3 – Calls are routed in the form of electrical signals via fiber optic cable. The fiber optic channel carries these signals to their destination in the form of light pulses.
  • Step 4 – Your call is forwarded to a regional center responsible for forwarding calls to remote central offices. Or forwarded to a central office (for local calls).
  • Step 5 – Finally, the terminal forwards the call to the appropriate phone number.

With PTSN Calling depending on where you are and where the call is going, your call will redirect. Let’s examine step 4 more.

  • CO: If you are in the same neighborhood as your recipient, your call will go to the local head office.
  • Tandem Office: If you’re in the same city as your recipient but elsewhere in the city, your call goes to your head office, then forwards to a tandem office. It is then directed to the central office of the person sought.
  • Toll Office: If you’re in another city or state from your recipient, then the tandem office would connect to a toll office (national long-distance switching).
  • International Gateway: If you are in a different country, your call will be forwarded here to connect your long distance call.

History of PSTN Calling

This system has been generally used since the late 1800s with underground copper wires carrying analog audio data. The history of PSTN begins in 1875 when American Alexander Bell founded the American Bell Telephone Company. In 1876, the use of telephones in private increased. At first, alerting another user to a request to make a phone call was accomplished by whistling loudly at the transmitter until the other party heard the alert. But that changed later. Bells have been added to signal, making the attendant’s job easier.

Then the exchange began, and each telephone was connected to a telephone exchange set up for a town or region. Bridges between power plants were established for different regions. The networks spanned cities, countries, continents, and oceans. However, people started to call the other person connected to the same exchange directly. But other regions required manual connection.

By the end of the 20th century, the Signaling System 7 (SS7) network emerged, which controlled calls between most exchanges. At the turn of the 21st century, the oldest parts of the telephone network still use analog technology for the last mile loop to the end-user. (A local loop in telephony is a physical link or circuit that connects from the border point of customer facilities to the edge of the common carrier’s or telecommunications service provider’s network.)

What is the difference between VoIP and PSTN?

VoIP (Voice over Internet Protocol) transmits real-time voice signals from one IP address to another. These audio signals are transmitted in a digital format. It takes place over the Internet. It can be between two phones or between a computer phone. PTSN Calling uses circuit-switched telephony between two points. It is a traditional method using copper wires. It is separate from internet traffic. It also includes cellular networks, switching centers, cable systems, and fiber optic cables.

Companies are already using Voice over Internet Protocol (VoIP) calling using a device of their choice. However, VoIP calling is like an intercom. It connects voice calls within the company, not the PSTN. VoIP uses the internet to connect, but PSTN uses a landline. Both have their own connection advantages. VoIP is customizable, but PSTN is configured with copper wires. It offers many additional services such as VoIP, call forwarding, voicemail. But PSTN Calling is for making calls only.

Major Benefits of Using PSTN

Although there are modern methods, we will examine why PSTN Calling is a good idea and its advantages. First, we can say that PSTN is purposeful. It was built for calling and does this task well. Most telecom operators offer extremely high levels of voice clarity. While security issues are so sensitive today, PSTN Calling has the advantage in this regard.

The PSTN continues to operate when there is a power outage, which means there is business continuity. This is the case because of its analog nature. It is easy to install and use. It is easy to install and use. Infrastructure installation is done by telecom companies. They even take care of you when you run into a problem. You can use PSTN Calling when you have an internet or VoIP problem.


The advancement of Internet technology has not made PSTN redundant or ineffective. There are companies that still use and even trust this system. PSTN Calling has many advantages. The largely analog nature of PSTN means that it is not vulnerable to attack. This is a reason for preference. You can choose this according to the needs and operation of your business.


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