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Do you remember the time when making a call actually meant something very specific?
You had a phone sitting in one place. You picked up the receiver, dialed each number one by one, and waited for the connection. There was a clear start, a clear end, and in many cases, a cost attached to how long you stayed on.
But underneath that experience was a very rigid setup. Calls were built on dedicated lines and once a connection was established, that line stayed reserved for the entire duration of the call.
Now compare that to how things work today.
You open WhatsApp or Discord, tap once, and you’re instantly connected with ‘Undertaker69’ from Netherlands and you can talk with him for as long as you want, just with an internet connection.
This change wasn’t the result of some sort of magic, rather, it came from a complete change in how voice communication works underneath the surface and like every major change in technology, it brought both convenience and new risks.
That is what we will be exploring in today’s piece. Let’s start!
What Voice Over Internet (VoIP) Means
Voice over Internet Protocol, or VoIP, is a method of transmitting voice over the internet instead of traditional telephone lines.
In older systems, a call required a dedicated connection between two points. That connection stayed active for the entire duration of the call, even if no one was speaking.
But VoIP handles this differently - your voice is converted into digital data, broken into smaller packets, and sent across the internet. These packets travel through networks just like any other type of data, independent of its format.
Because of this change, the system focuses on delivering data efficiently. Packets can take different routes before reaching their destination, depending on network conditions, which allows the voice to be integrated into platforms, combined with other features, and scaled without relying on traditional telecom systems.
That’s why modern communication tools treat voice as a part of a larger environment.
How Voice Over Internet (VoIP) Works
At a basic level, VoIP follows a structured process.
When you speak into a device, your voice is captured as an analog signal. That signal is converted into digital form using codecs, which prepare the data for transmission. The data is then compressed and divided into smaller packets.
These packets are sent across the internet using packet switching. Unlike traditional systems, there is no single fixed path. Each packet can take a different route depending on network availability.
On the receiving side, those packets are collected, reassembled, decompressed, and converted back into audio.
The process happens quickly enough that it feels like a real-time conversation, but the underlying behavior is very different from traditional telephony because everything depends on network conditions, factors like latency, packet loss, and jitter can affect call quality. This is the trade-off. The system gains flexibility and scalability, but it becomes dependent on the quality of the internet connection.
There is also a coordination layer involved. Systems use protocols such as Session Inition Protocol (SIP) to establish, manage, and terminate calls. These protocols handle the signaling side of communication, ensuring both ends know when a session starts and ends.
How Voice Calling Worked in the Past
Before voice moved onto the internet, communication ran through traditional telephone networks built on circuit-switched systems.
These systems relied on in-band signaling, where the same line carried both voice and the control signals that told the network what to do. Routing a call, marking a line as busy, connecting long-distance, all of it depended on specific tones moving through the line.
The design worked well for its time, but the system trusted whatever signal it received and that assumption turned out to be a big problem.
As covered in the earlier phreaking piece, people eventually figured out that if the network responded to tones, those tones could be reproduced. Once that happened, the system could be influenced from the outside.
Over time, it became clear that this approach couldn’t be secured through small fixes. The entire design needed to change which led to a transition where control signals were separated from voice communication. Instead of relying on tones coming through the same line, signaling moved to dedicated systems like Signaling System No. 7 (SS7).
If you want to dive into more details regarding how earlier telephones worked and what phreaking is, you can check out the following piece:
Important Note
It’s easy to assume that VoIP replaced older telephone systems like Signaling System No. 7 (SS7) or was introduced to fix issues like phreaking, but keep in mind that this is NOT correct.
SS7 belongs to traditional telecom infrastructure. It was introduced to separate control signals from voice and reduce the kind of weaknesses exposed in earlier systems, while VoIP treats voice as data and sends it over packet-based networks instead of dedicated lines.
These technologies exist at different layers and solve different problems.
Early Foundations of Voice over Internet (VoIP)
Now that the fundamentals are clear, it makes sense to step back and look at how all of this began.
Voice over the internet came from decades of experimentation around how voice could be processed, transmitted, and eventually detached from physical communication systems.
To understand where we are today, we need to move through that timeline.
Pre-VoIP Era
1920s–1960s: Early Voice Research
The foundations of VoIP can be traced back to 1925, when AT&T and Western Electric established Bell Labs to advance communication technologies.
A major breakthrough came in 1939, when engineer Homer Dudley developed the Voder, the first electronic voice synthesizer. It used oscillators, filters, and manual controls to recreate human speech, demonstrating that voice could be generated and manipulated electronically.
