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Circuit Switching

Circuit switching is a method of network communication where a dedicated communication path or circuit is established between two endpoints for the duration of the session. This technique is primarily associated with traditional telephone networks but can also be applied in some data communication contexts. Here’s a detailed explanation of circuit switching, including its working principles, characteristics, and an example.

1. Definition and Key Concepts

  • Dedicated Path: A specific, exclusive path is established for the duration of the communication session.
  • Continuous Connection: Once the circuit is set up, the connection remains active until the communication ends.
  • Fixed Bandwidth: The resources (bandwidth) allocated to the circuit remain constant throughout the session.

2. Stages of Circuit Switching

The process of circuit switching involves three main stages: circuit establishment, data transfer, and circuit disconnection.

a. Circuit Establishment

  • Call Initiation: The sender initiates a call by dialing the receiver’s number.
  • Switching Nodes: Intermediate switching nodes (exchanges) determine the optimal path from the sender to the receiver.
  • Path Setup: A temporary dedicated path is established through these nodes, reserving the required bandwidth and resources.
  • Ringing and Connection: The receiver’s device rings, and once the receiver answers, the circuit is completed, and the communication can begin.

b. Data Transfer

  • Continuous Data Flow: Data flows continuously between the sender and receiver over the dedicated path.
  • Low Latency: Since the path is dedicated, there is minimal delay, ensuring real-time communication.
  • Quality of Service: The dedicated nature of the circuit ensures a consistent quality of service (QoS).

c. Circuit Disconnection

  • Call Termination: Once the communication session ends, either party can terminate the call.
  • Resource Release: The circuit is disconnected, and the reserved resources are freed up for other users.

3. Characteristics of Circuit Switching

  • Dedicated Resources: Resources are exclusively reserved for the entire duration of the communication.
  • Constant Bandwidth: The bandwidth allocated to the circuit remains constant and is not shared with other users.
  • Real-Time Communication: Ideal for applications requiring real-time, uninterrupted communication, such as voice calls.

4. Advantages and Disadvantages

Advantages

  • Low Latency: Provides minimal delay due to the dedicated path, making it suitable for real-time applications.
  • High Quality of Service: Ensures consistent and predictable performance.
  • Simplicity: Well-understood technology with straightforward implementation in traditional telephony.

Disadvantages

  • Inefficient Resource Utilization: Resources are reserved whether or not data is being transmitted, leading to potential inefficiencies.
  • Scalability Issues: Limited ability to handle large volumes of simultaneous connections due to fixed resources.
  • High Cost: Maintaining dedicated circuits can be expensive, especially for long-distance communication.

5. Example of Circuit Switching

Consider a traditional landline telephone call:

Step-by-Step Example

  1. Caller Dials Number: Alice wants to call Bob, so she picks up her landline phone and dials Bob’s number.
  2. Call Setup:
    • Alice’s phone sends a signal to her local telephone exchange.
    • The local exchange identifies Bob’s number and determines the path to Bob’s phone.
    • If Bob is on a different exchange, the local exchange routes the call to an intermediate exchange, which then routes it to Bob’s local exchange.
  3. Path Establishment:
    • The telephone network establishes a dedicated circuit from Alice’s phone to Bob’s phone through the involved exchanges.
    • Each segment of the path reserves the necessary resources and bandwidth.
  4. Ringing and Connection:
    • Bob’s phone rings, and when he picks up, the circuit is completed.
    • Alice and Bob can now communicate with each other in real-time.
  5. Data Transfer:
    • During the conversation, voice signals (converted into electrical signals) travel continuously along the dedicated circuit.
    • The dedicated path ensures low latency and high-quality voice transmission.
  6. Call Termination:
    • When Alice or Bob hangs up, the circuit is disconnected.
    • The resources reserved for the call are released and made available for other users.

6. Modern Context and Evolution

  • Legacy Use: While circuit switching is the backbone of traditional telephone networks (PSTN), its use in modern data networks has diminished.
  • Transition to Packet Switching: Modern telecommunications have largely transitioned to packet-switched networks (e.g., the Internet), which are more efficient and scalable.
  • Voice over IP (VoIP): Voice communication is increasingly moving to VoIP, which uses packet-switched networks to transmit voice data, reducing the reliance on traditional circuit-switched networks.

Conclusion

Circuit switching provides a dedicated, high-quality communication path, making it ideal for real-time applications like voice calls. However, its inefficiencies and limitations in handling large volumes of data and connections have led to a shift towards packet-switched networks in modern communication systems. Understanding circuit switching helps appreciate the evolution of communication technologies and the foundational principles of network design.