Circuit Switching Explained: Definition, Examples, and Moder

August 19, 2025

Circuit Switching: What It Is and Why It No Longer Powers the Internet

Introduction

Before the internet and modern IP-based networks, communication systems were dominated by circuit switching—the foundation of traditional telephone systems. While mostly obsolete in today’s data-driven world, understanding circuit switching helps explain why modern networks were designed the way they are.

In this guide, we’ll explain what circuit switching is, how it works, where it was used, and how it compares to today’s dominant model: packet switching. Finally, we’ll explore how noBGP introduces a new approach to deterministic and programmable routing, without the pitfalls of legacy networking.

What is Circuit Switching?

Circuit switching is a method of communication where a dedicated communication path is established between two endpoints for the entire duration of a session.

Key Characteristics:

Dedicated path: Once established, no other traffic can use the circuit.
Consistent performance: Predictable latency and bandwidth.
No data sharing: The path remains reserved even when idle.

How Circuit Switching Works

Circuit switching involves three phases:

Connection Setup
A signaling protocol reserves a dedicated path through each intermediate switch.
Data Transfer
The connection remains open for the duration of the call or session.
Connection Teardown
Once communication ends, the circuit is dismantled and resources are released.

Real-World Example: Traditional Telephone System

When you dial a phone number using a landline:

Your phone connects to a local switch.
That switch creates a path through several intermediate switches.
A continuous analog circuit is reserved between your phone and the recipient’s.

Even if neither person speaks for 30 seconds, the entire path remains dedicated and unavailable to others.

Diagram: Circuit Switching in Action

[Caller]───[Switch A]───[Switch B]───[Switch C]───[Recipient] ←────────── Dedicated Circuit ─────────→

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Once the call begins, the same physical or logical path is used until the call ends.‍

Advantages of Circuit Switching

Benefit	Description
Predictable performance	No packet delays or reordering
Fixed bandwidth	Guaranteed availability during the session
Low latency	No routing decisions needed during call

Disadvantages of Circuit Switching

Drawback	Description
Inefficient for data	Circuit is reserved even when idle
Poor scalability	Requires dedicated resources per connection
High setup overhead	Connection must be established before use
Not suited for bursty traffic	Ideal for continuous streams like voice

Circuit Switching vs Packet Switching

Feature	Circuit Switching	Packet Switching
Connection type	Dedicated path	Dynamic routing
Resource allocation	Reserved per connection	Shared across packets
Ideal for	Voice (analog)	Data (digital)
Efficiency	Low	High
Scalability	Poor	Excellent

Modern networks use packet switching (e.g., IP, TCP/UDP) because it handles bursty, asynchronous data far more efficiently.

Where Circuit Switching Is Still Used

While rare in data networks, circuit switching still finds use in:

Traditional telephony (PSTN)
Some legacy PBX systems
Dedicated leased lines
Military and aviation systems (where deterministic paths are required)

Most modern systems—even VoIP and 5G—use packet switching underneath, but may simulate circuit-like behavior using Quality of Service (QoS) and session control protocols.

The Shift from Circuit to Cloud-Native Networking

In the past, networking was static. Paths were defined manually and didn’t change. Circuit switching embodied this approach.

Today, applications are:

Ephemeral: Services spin up and down on demand
Distributed: Across data centers and clouds
Dynamic: Require elastic bandwidth and fast failover

Networking must adapt to these patterns, which circuit switching cannot support.

How noBGP Moves Beyond Circuit Switching (and Packet Guesswork)

While packet switching replaced circuit switching for efficiency, it introduced a new problem: non-determinism. In modern networks, you don’t know which path your packets will take—BGP decides, not you.

noBGP reintroduces determinism and path control—without the downsides of circuit switching.

How noBGP Improves on Legacy Models:

Deterministic routing: You define which paths are allowed, blocked, or prioritized.
Private connections: End-to-end encryption with zero public exposure.
Service-based networking: Connections are based on identity, not IPs.
Dynamic provisioning: Paths adapt in real time without needing a reserved circuit.

Unlike packet switching with BGP, which can send your traffic through random ISPs, noBGP gives you control and visibility.

Summary: Circuit Switching vs Modern Alternatives

Feature	Circuit Switching	Packet Switching	noBGP
Routing Control	✅ Total	❌ None	✅ Policy-based deterministic
Scalability	❌ Low	✅ High	✅ High
Idle Resource Waste	❌ Yes	✅ No	✅ No
End-to-End Privacy	❌ None	❌ Depends	✅ Built-in encryption
Setup Speed	❌ Slow	✅ Fast	✅ Instant
Cloud & App Awareness	❌ None	❌ Low	✅ Yes

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Final Thoughts

Circuit switching served the world well during the analog voice era. But it doesn’t scale, doesn’t adapt, and doesn’t support the flexibility modern apps demand. Packet switching took over, but came with its own challenges—especially a lack of control over data paths.

noBGP offers a third option: the performance control of circuit switching, the efficiency of packet switching, and the programmability of modern software.

It’s time to leave both legacy systems behind and choose your path—with noBGP.

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