By: John Shepler

Over the past few decades, two primary network technologies have been vying for dominance. The first is the traditional telephone system, which served us well throughout the industrial age. The second is the computer-based architecture that has driven the information age. You might recognize these as circuit switching and packet switching.

While both technologies will likely coexist for a while longer, we are at a turning point. From now on, packet switching will be the dominant force in every network, from copper lines to fiber optic cables to wireless connections. Let’s explore why.

What is Circuit Switching?

Circuit switching is a telephone-based technology. This system is logical for telephone calls because they need a dedicated connection between two devices for a specific period. Certain phones, like intercoms, can have a permanent, or “nailed up,” connection. For general use, any phone should connect to any other phone, but the connection is only needed for the call’s duration.

The central office switch makes this possible. It physically links the lines from any two phones using electrical switches. Years ago, multiple homes in a neighborhood might share a single line to the central office. This “party line” allowed anyone to listen in on their neighbor’s calls. With the introduction of automatic dialing, party lines became less popular, and each location got its own line and phone number. Connected phones had their own dedicated electrical circuit, which is where the term “circuit switching” originates.

Circuit Switching For Digital Lines

When long-distance calls transitioned from analog to digital, circuit switching remained the core concept. For example, a T1 line is split into 24 individual channels, each carrying a separate phone call as if on distinct wires.

T1 lines found a new use in connecting computers, enabling them to “talk” to each other. However, each channel only allows for 64 Kbps of data, which is equivalent to dial-up speed. A broadband circuit, reaching speeds of 1.5 Mbps, can be created by merging all the channels into a single transmission line. Like their analog predecessors, these circuits require a continuous, or “nailed up,” connection for computers to interact. Circuit switching works well for point-to-point communication, but what if many machines need to communicate at or near the same time?

What is Packet Switching?

Packet switching was invented to allow information sharing among numerous devices. It’s like a reimagined party line. However, unlike the old analog system, multiple “conversations” must happen concurrently without interfering with each other. If devices randomly sent bits of data onto the line, it would be chaos. Instead, the information intended for each network node is grouped into independent units called packets.

Packets contain pieces of data and address bits indicating their origin and destination. This is what enables packet switching. Instead of dialing a number to establish circuits, network switches and routers guide the packets using the addresses within them. Multiple devices can use the network line simultaneously as long as the traffic is managed effectively, and each packet includes its destination address.

Circuit vs Packet

Computer-based packet networks and telephone-based circuit networks have existed side-by-side for quite a while. The largest circuit-switched network is the PSTN, or Public Switched Telephone Network. The Internet holds the title of the largest packet-switched network. What we’re seeing now is a convergence of these two technologies.

Maintaining a single network is more efficient than managing two separate ones, and combining voice and data traffic on the same network opens up possibilities for additional services. But which technology comes out on top: circuit or packet switching?

And the Winner Is….

Packet switching is the clear winner, especially since global computer traffic has surpassed voice traffic. Computer traffic now includes digitized video, which alone surpasses the combined volume of voice and data. All of these utilize packet switching technology across the internet and private networks. As wireless voice communication shifts from dedicated cellular systems to packet-based 4G networks, the transition from circuit-switched to packet-switched networks will be complete.

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