What is Circuit Switching?

Updated on July 22, 2025

Circuit switching is the foundation of traditional telecom networks. It creates a dedicated communication channel between network nodes before any data is sent. Unlike packet switching, it reserves a fixed path and bandwidth for the entire session.

Understanding circuit switching is essential for IT professionals working with network infrastructure, particularly those managing legacy systems or implementing dedicated communication channels. This switching method continues to play a crucial role in modern networking, from traditional telephony to optical data center applications.

Definition and Core Concepts

Circuit switching is a method of implementing a telecommunications network in which two network nodes establish a dedicated communications channel (circuit) through the network before the nodes may communicate. This circuit guarantees the full bandwidth of the channel and remains exclusively connected for the duration of the communication session, functioning as if the nodes were physically connected.

The fundamental principle behind circuit switching involves creating a temporary but exclusive pathway between the sender and receiver. Once established, this pathway remains dedicated to that specific communication session until explicitly terminated.

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Dedicated Communication Channel (Circuit)

A dedicated communication channel represents the core of circuit switching. This channel consists of a continuous pathway through the network that connects the sending and receiving nodes. The pathway includes all intermediate switches, transmission lines, and network resources required to maintain the connection.

Exclusive Use

Circuit switching guarantees exclusive use of the allocated resources. No other communication sessions can use the same pathway or bandwidth allocation during an active connection. This exclusivity ensures predictable performance characteristics throughout the communication session.

Guaranteed Bandwidth

The system reserves a fixed amount of bandwidth for each circuit. This bandwidth remains constant regardless of actual data transmission requirements. Whether the connection actively transfers data or remains idle, the allocated bandwidth stays reserved for that specific circuit.

Connection Establishment Phase

Before any data transfer can occur, the network must establish a complete circuit between the communicating nodes. This process involves locating available resources, reserving them, and configuring all intermediate switches along the path.

Data Transfer Phase

Once the circuit is fully established, data flows continuously along the dedicated path. The network treats the connection as a permanent pathway, eliminating the need for routing decisions during data transmission.

Circuit Disconnection Phase

When either party terminates communication, the network releases all reserved resources. This process makes the previously allocated bandwidth and switching resources available for other connections.

Physical Layer Association

Circuit switching originally operated at the physical layer, where actual physical connections were established between communicating parties. Modern implementations may virtualize these connections while maintaining the same logical principles.

Contrast with Packet Switching

Unlike packet switching, which divides data into independent packets that share network resources, circuit switching maintains a continuous, dedicated connection. Packet switching makes routing decisions for each individual packet, while circuit switching establishes the complete path before any data transmission begins.

How It Works

Circuit switching operates through three distinct phases that ensure reliable, dedicated communication between network nodes.

Circuit Establishment

The circuit establishment process begins when a sender initiates a connection request to communicate with a specific receiver. This request triggers a series of network operations designed to create a dedicated pathway.

Network switches along the potential path must locate and reserve an available, continuous route from sender to receiver. Each switch examines its available outgoing connections and reserves the necessary resources for the proposed circuit. The process continues hop by hop until reaching the destination node.

Resources such as bandwidth, switch buffers, and transmission capacity are dedicated and reserved for the entire duration of the potential connection. These resources remain unavailable to other connections even during periods of no active data transmission.

A signaling protocol, such as Signaling System 7 (SS7) in telephony networks, may coordinate the circuit establishment process. This protocol operates on a separate control channel to set up the circuit without interfering with actual data transmission.

Data Transfer

Once the circuit is fully established, data flows continuously along the dedicated path. The network treats this path as a permanent connection, eliminating the need for packetization, reassembly, or routing decisions during data transfer.

The dedicated nature of the circuit provides constant bit delay, fixed data rate, and consistent quality throughout the communication session. Applications can rely on predictable performance characteristics without worrying about network congestion or variable routing delays.

Data transmission occurs in real-time without the overhead typically associated with packet processing. The network simply maintains the established circuit and ensures data flows smoothly between the connected nodes.

Circuit Disconnection

When either party terminates communication, a disconnection signal is sent through the network control channels. This signal instructs all switches along the path to release their reserved resources.

Switches systematically free the previously allocated bandwidth, buffer space, and switching capacity. Once released, these resources become immediately available for establishing new circuits or serving other network functions.

The disconnection process ensures efficient resource utilization by preventing abandoned circuits from consuming network capacity indefinitely.

Key Features and Components

Circuit switching exhibits several distinctive characteristics that differentiate it from other networking approaches.

Dedicated Path

Each communication session receives an exclusive pathway through the network. This path remains constant throughout the entire session, providing predictable routing and consistent performance characteristics.

Fixed Bandwidth Allocation

The network allocates a specific amount of bandwidth to each circuit during establishment. This allocation remains constant regardless of actual usage patterns or transmission requirements.

Predictable Performance

Circuit switching delivers constant delay, low jitter, and consistent quality throughout the communication session. Applications can rely on these predictable characteristics for time-sensitive operations.

Continuous Data Flow

Data flows continuously along the established circuit without interruption or processing delays. The network maintains the connection as a permanent pathway until explicitly terminated.

Connection-Oriented Nature

Circuit switching requires explicit connection establishment before data transmission can begin. This connection-oriented approach ensures that both parties are ready to communicate before allocating network resources.

Resources Reserved During Idle Periods

Allocated resources remain reserved even when no active data transmission occurs. This characteristic can lead to inefficient resource utilization during periods of low communication activity.

Use Cases and Applications

Circuit switching finds application in scenarios requiring guaranteed performance, dedicated bandwidth, or predictable communication characteristics.

Traditional Telephony (PSTN)

The Public Switched Telephone Network (PSTN) represents the defining example of circuit switching implementation. Each telephone call establishes a dedicated circuit between the calling and called parties, maintaining this connection throughout the conversation duration.

Emergency Services

Emergency communication systems often rely on circuit switching to ensure highly reliable and predictable communication channels. These applications cannot tolerate the variable delays or potential packet loss associated with shared network resources.

Private Networks

Businesses requiring dedicated, high-quality connections between specific locations often implement circuit-switched solutions. These networks provide guaranteed bandwidth and consistent performance for critical business communications.

Video Conferencing Systems

Traditional dedicated video conferencing systems use circuit switching to ensure consistent data streams for high-quality video transmission. The guaranteed bandwidth and low jitter characteristics support real-time video communication requirements.

Dial-Up Internet Connections

Historical dial-up internet connections utilized the circuit-switched telephone network to establish dedicated pathways between users and Internet Service Providers (ISPs). Each connection required a complete circuit through the telephone network.

Optical Circuit Switching

Modern data centers implement optical circuit switching to establish dedicated light paths using Wavelength-Division Multiplexing (WDM) and Reconfigurable Optical Add/Drop Multiplexers (ROADMs). These systems provide high-bandwidth, low-latency connections for specific applications.

Advantages and Trade-offs

Circuit switching offers specific advantages while introducing certain limitations that must be considered when selecting networking approaches.

Advantages

• Guaranteed Quality of Service (QoS): Circuit switching ensures consistent bandwidth, low latency, and minimal jitter throughout the communication session. This predictability makes it ideal for real-time applications requiring stable performance characteristics.
• Reliability: Once established, the connection remains stable and continuous until explicitly terminated. The dedicated nature of the circuit eliminates concerns about network congestion affecting communication quality.
• Simplicity of Data Transfer: The network requires no per-packet processing overhead during transmission. Data flows continuously along the established path without routing decisions or protocol processing delays.
• Security: Circuit switching provides a relatively secure and exclusive channel, reducing the risk of interception by others sharing the network. The dedicated pathway limits exposure to potential security threats.

Limitations and Trade-offs

• Resource Inefficiency: Bandwidth remains reserved and unused during periods of silence or low activity. This inefficiency can significantly impact network utilization, particularly in applications with bursty or intermittent communication patterns.
• High Setup Time: Connection establishment can take considerably longer compared to connectionless methods. The need to reserve resources and configure intermediate switches introduces delays before data transmission can begin.
• Scalability Issues: The network struggles to handle large volumes of simultaneous connections efficiently due to resource reservation requirements. Each additional circuit consumes dedicated network resources regardless of utilization levels.
• Higher Cost: Maintaining dedicated circuits can be more expensive than shared resource approaches. The exclusive allocation of network resources increases operational costs, particularly for underutilized connections.
• Lack of Flexibility: The fixed path cannot adapt to changing network conditions or failures during a communication session. If network topology changes or better paths become available, the established circuit cannot take advantage of these improvements.
• Communication Breakdown on Path Failure: If any component of the dedicated path fails, the entire communication session breaks down. The network cannot automatically reroute traffic around failed components without establishing a completely new circuit.

Key Terms Appendix

• Circuit Switching: A communication method establishing a dedicated channel between two nodes for the duration of a session.
• Dedicated Channel (Circuit): An exclusive communication path reserved for a single connection.
• PSTN (Public Switched Telephone Network): The traditional landline telephone system, a prime example of circuit switching.
• Bandwidth: The maximum rate of data transfer.
• QoS (Quality of Service): The ability to provide different priority to different applications or data flows.
• Latency: The delay in data transmission.
• Jitter: The variation in packet delay.
• Packet Switching: A communication method where data is divided into independent packets that share network resources.
• SS7 (Signaling System 7): A set of telephony signaling protocols.
• WDM (Wavelength-Division Multiplexing): A technology used in optical networks to transmit multiple light signals over a single fiber.
• ROADMs (Reconfigurable Optical Add/Drop Multiplexers): Devices in optical networks used to add, drop, or pass wavelengths.