Public Switched Telephone Network (PSTN

 ###  Public Switched Telephone Network (PSTN)

#### 1. Introduction to PSTN

**Definition and Purpose:**

- **Public Switched Telephone Network (PSTN)** is the world's collection of interconnected voice-oriented public telephone networks, both commercial and government-owned.

- It is designed for voice communication and provides reliable and high-quality voice services.

- **Difference from Other Networks:**

  - **PSTN:** Traditional landline telephone network using circuit-switched technology.

  - **Cellular Networks:** Wireless communication using radio waves.

  - **VoIP (Voice over Internet Protocol):** Uses internet protocols for voice communication.

**History:**

- Invented by Alexander Graham Bell in 1876.

- Evolution from manual switchboards to automated electromechanical and digital switches.

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#### 2. Basic Concepts

**Analog and Digital Signals:**

- **Analog Signals:** Continuous waveforms that vary in amplitude and frequency, used in traditional telephony.

- **Digital Signals:** Discrete binary values (0s and 1s), providing better quality and efficiency.

**Circuit Switching:**

- A method of communication where a dedicated communication path is established between two parties for the duration of the call.

- Ensures a constant and reliable connection with consistent quality.

**Components of PSTN:**

- **Telephones:** Devices used to send and receive voice signals.

- **Switches:** Devices that connect calls between telephones.

- **Transmission Media:** Physical paths like copper wires and fiber optics that carry signals.

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#### 3. How PSTN Works

**Call Setup and Termination:**

- **Step-by-Step Process:**

  - **Dialing:** User dials the telephone number.

  - **Routing:** The local switch identifies the destination and routes the call through intermediate switches if necessary.

  - **Connection Establishment:** A dedicated circuit is established for the call duration.

  - **Call Termination:** Connection is released after the call ends.

**Switching Techniques:**

- **Local Exchange:** Connects calls within a local area.

- **Tandem Exchange:** Connects local exchanges within a region.

- **International Exchange:** Connects calls between different countries.

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#### 4. Modernization of PSTN

**Digital Switching:**

- Transition from analog to digital switching systems improves efficiency and call quality.

- Digital switches use time-division multiplexing (TDM) to handle multiple calls simultaneously.

**Integration with Internet Protocol (IP) Networks:**

- **VoIP:** Allows voice communication over IP networks, interconnecting with PSTN.

- **Gateways:** Convert voice signals between PSTN and IP networks.

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#### 5. PSTN Today

**Current Uses:**

- Still widely used for residential and business telephony.

- Reliable for emergency services (911).

**Challenges and Limitations:**

- **Technical:** Limited bandwidth, analog noise, and signal degradation over long distances.

- **Infrastructural:** High maintenance costs and aging infrastructure.

**Future Trends:**

- Shift towards full IP-based communication systems.

- Development of more advanced telecommunication technologies.

**Questions:**

1. What is PSTN?

2. How does circuit switching differ from packet switching?

3. Name three components of PSTN.

4. What are the differences between analog and digital signals?

5. How does VoIP integrate with PSTN?