What Is PSTN?

PSTN stands for Public Switched Telephone Network. The public switched telephone system has been around in some form since the late 1800s, ultimately allowing callers to communicate with anyone around the world.

Often referred to as landlines, fixed lines, or analog, PSTN traditionally uses underground copper wires, switches, and other infrastructure to connect calls. Parts of the legacy system have now been upgraded to digital, but the network continues to be heavily regulated by government bodies to ensure fair access, pricing, and service quality.

How Does PSTN Calling Work?

PSTN calling operates through a network of interconnected switches and circuits. When you make a call, the phone converts your voice into electrical signals, which are sent to the local exchange. This exchange, using a system of routing protocols, determines the most efficient path for the call to take through a series of intermediate switches and trunk lines, which are high-capacity transmission lines.

Components of PSTN

There are a few essential components enabling phone calls:

• Local loops, which are physical wires linking homes and businesses to local exchanges. These are responsible for transmitting voice signals.

• Switches at exchanges route calls, optimizing local and long-distance connections.

• Trunk lines act as network highways, handling multiple calls simultaneously across different exchanges using copper, fiber optics, or microwave transmission.

Call Setup and Routing Process

Initiating a PSTN call involves dialing the recipient's number, which the local exchange uses to determine the optimal routing path. This path is established through interconnected switches and exchanges, creating a dedicated circuit for uninterrupted communication.

Circuit-Switched Technology

Circuit-switched technology is a key part of PSTN. When you make a call, a dedicated communication path is established between you and the person you're calling for the entire duration of the conversation. This process starts when you dial a number, prompting the local exchange to create a temporary, dedicated circuit through a series of switches and trunk lines. Each switch in the network sets up a connection to the next, ensuring that a continuous and exclusive path is maintained.

This dedicated circuit guarantees a stable and consistent quality of the call, as the communication line is not shared with other users until the call is ended. Once the call is finished, the circuit is released and becomes available for other calls.

PSTN Architecture

The architecture of the Public Switched Telephone Network (PSTN) consists of four main elements, each playing a critical role in the call routing process. These elements create a seamless and efficient network for managing local, regional, long-distance, and international calls.

1. The local exchange is the entry point for calls, connecting individual subscribers through local loops to the broader network. It handles call setup, routing, and termination within a local area. It might also be referred to as a switching exchange, or a central office.

2. The tandem office connects multiple local exchanges within a region, enabling efficient routing of calls that do not require long-distance handling but need to be transferred between local exchanges. It is also known as a transit switch or junction network.

3. The toll office comes into play for long-distance calls, connecting tandem offices and handling the routing of calls over long distances, often between different regions or cities.

4. The international gateway serves as the connection point for international calls, interfacing with foreign telephone networks and handling the routing and translation of signaling protocols to ensure smooth cross-border communication.

What Are the Key Features of a PSTN Phone System?

PSTN has been a popular communication system for many years, offering convenient features such as:

• Reliability. PSTN is known for "five nines" reliability (99.999% operational time), thanks to redundant infrastructure and backup routes. This ensures consistent and dependable service even during peak times or emergencies.

• Voice Quality. Calls made through a PSTN meet a high standard of voice quality. This results in clear and uninterrupted voice communication, essential for both personal and professional use.

• Global Connectivity. Interconnected networks and provider agreements allow calls to be made to nearly any location worldwide. This extensive reach makes it a cornerstone for international business, and allows people across the world to stay connected.

• Interoperability. Users across different service providers can communicate seamlessly, enhancing global utility and accessibility. This compatibility ensures that users do not face barriers due to differing service providers, allowing them to make calls to whoever, whenever.

Three Benefits of PSTN

Although many businesses now prefer to use a digital system like a VoIP phone service, PSTN remains a popular choice for a few key reasons. Let’s take a look at some of the main benefits of PSTN:

1. Established Infrastructure

One of the great things about PSTN is its built-in infrastructure which has been developed and improved over many years. This infrastructure includes a huge network of local exchanges, switches, trunk lines, and international gateways that cover the whole world. This well-established physical network ensures that PSTN provides reliable and widespread coverage.

2. Consistent Call Quality

PSTN uses dedicated circuits for each call, ensuring clear and reliable voice communication with minimal latency and interference. This reliability in voice quality makes PSTN particularly valuable for businesses and critical communications where clarity and dependability are crucial.

3. High Security and Privacy

PSTN operates on a closed, dedicated network with stringent security measures in place. PSTN phone line providers also adhere to strict regulations and encryption standards to safeguard user privacy and prevent unauthorized access to communications. This high level of security makes PSTN a trusted choice for organizations that rely on sensitive communications, such as government agencies, financial institutions, and businesses that prioritize confidentiality and data protection.

Common Challenges or Limitations to PSTN

As with all legacy systems, there are a number of challenges that come with PSTN phone lines. These include:

High Operational Costs

PSTN's reliance on dedicated circuits also means it can be costly to maintain and expand, especially for long-distance or international calls. The costs include maintenance of aging equipment, periodic upgrades to support new technologies or regulatory requirements, and expenses associated with physical facilities. This can result in higher line rental costs and increased call charges for businesses, especially for long-distance and international calls. Equipment upgrades may also lead to delays and outages, further adding to your operational costs.

Limited Scalability

One of the common challenges with PSTN is its dependency on physical infrastructure, such as copper wires and traditional circuit-switched technology. This can limit the flexibility and scalability of the network compared to modern digital systems like VoIP (Voice over Internet Protocol).

Slow Adaptation to Modern Digital Needs

As technology evolves, PSTN faces challenges in integrating seamlessly with digital communication services and supporting advanced features like video conferencing and real-time collaboration without additional adaptations or upgrades.

PSTN vs. PBX: What Is the Difference?

The Public Switched Telephone Network and Private Branch Exchange (PBX) are two distinct telecommunication systems.

PSTN uses traditional landlines and public telephone networks to support analog voice communication. It is highly reliable and provides extensive coverage, making it ideal for personal and business use worldwide. However, it can be expensive, particularly for long-distance calls, and offers limited scalability and flexibility in handling modern communication needs.

In contrast to PSTN, a PBX is a private telephone network used within an organization. It allows internal communication and manages incoming and outgoing calls through its own switchboard. Nowadays, many PBX systems leverage VoIP technology to route calls over the internet, offering lower costs and advanced features like voicemail, call forwarding, and conference calling.

Other PSTN Alternatives

The good news is there are plenty of reliable and affordable alternatives to PSTN. Let’s compare the top contenders below.

PSTN v. ISDN

ISDN is a digital telecommunications network that integrates voice, data, and video services over the same physical lines, providing higher quality and faster transmission speeds compared to PSTN. ISDN uses digital circuit-switched technology, allowing for multiple simultaneous connections and offering enhanced features like call forwarding and conferencing.

While PSTN is known for its extensive coverage and reliability, ISDN provides better performance and versatility, albeit often at a higher cost and with more complex setup requirements.

PSTN vs. VoIP

What is a VoIP phone exactly? VoIP converts voice signals into digital data packets and transmits them over the internet or other IP-based networks. VoIP offers greater flexibility, lower costs — especially for international calls — and a range of advanced features such as video conferencing, call forwarding, and voicemail.

However, VoIP's reliability and call quality can be affected by internet speed and bandwidth, making it dependent on a robust and stable internet connection.

How Much Does PSTN Access Cost?

The cost of PSTN access can vary widely based on several factors, including the service provider, the location, and the specific services included. Here's a breakdown of typical cost components:

1. Installation fees. If there isn’t a line already in place, setting up a new PSTN line can involve an initial installation fee. This can range from $50 to $200 depending on the provider and location.

2. Monthly line rental. The monthly rental fee for maintaining a PSTN line generally ranges from $20 to $50 per line. This fee covers the basic service and maintenance of the line.

3. Local and long-distance rates. Local calls are often included in the monthly line rental or charged at a low rate, but long-distance and international calls can add significantly to the cost. Rates for long-distance calls vary widely, typically ranging from a few cents per minute to higher rates depending on the distance and destination.

4. Additional features. Adding features such as voicemail, caller ID, call waiting, and call forwarding can increase the monthly cost by $5 to $15 per feature.

5. Business plans. Businesses may opt for multi-line plans or bundled services that can range from $50 to several hundred dollars per month, depending on the number of lines and additional services required.

Four Reasons Why VoIP Is Better Than PSTN

Voice over Internet Protocol is an increasingly popular alternative to PSTN – here’s why.

1. Enhanced Cost Efficiency

VoIP offers enhanced cost efficiency compared to PSTN by utilizing internet connections to transmit voice data. This significantly reduces or eliminates long-distance and international call charges. Plus, VoIP solutions often include advanced features at minimal or no extra cost. 

2. Improved Customer Service

Connecting PSTN and IP calls allows you to leverage powerful features like call forwarding, automated attendants, and integration with CRM systems. These tools make it easier to manage and respond to customer inquiries promptly, empowering businesses to offer a more efficient and personalized service compared to the limited functionality of PSTN.

3. Increased Productivity

With advanced features like virtual meetings, instant messaging, and seamless integration with other business applications, VoIP allows for more efficient communication and collaboration. These capabilities streamline workflows and reduce the time spent on managing calls, unlike the basic services provided by PSTN.

4. Greater Scalability

VoIP offers greater scalability by allowing businesses to easily add or remove lines and features as needed without significant infrastructure changes or costs. Having this flexibility is essential for growing businesses; on the other hand, PSTN requires more complex and costly adjustments to accommodate expansion.

What Does the Future Hold for PSTN?

PSTN has declined in usage as digital communication technologies like VoIP and mobile networks become more prevalent and cost-effective. Businesses are increasingly moving away from traditional PSTN in favor of modern alternatives, which offer greater flexibility, advanced features, and lower costs.

In some areas, PSTN is being phased out entirely. The Netherlands and Estonia have already turned off their PSTN networks, while places like the United Kingdom, New Zealand, and Denmark have committed to terminating the system within the next six years.

Transition strategies often involve adopting hybrid systems that integrate both PSTN and VoIP to ensure a smooth migration. As emerging technologies such as 5G and IoT continue to evolve, they provide superior connectivity and innovative communication solutions.

Safeguard Your Communications and Contact Vonage

PSTN has been a cornerstone of global communication since its inception in the late 1800s. Despite its established infrastructure and reputation for reliability, PSTN is facing a decline in usage due to the rise of digital technologies like VoIP and mobile networks. Businesses are turning to these alternatives because they bring significant benefits, including improved cost efficiency, advanced features, and flexibility.

Contact us today to see Vonage’s advanced solutions in action, and find out how switching to VoIP can help you.