The Inventor of VoIP - Marian Croak

One year after the Supreme Court of the United States ruled that public schools must be desegregated in the landmark, historical case of Brown v. Board of Education, Marian Croak was born.

Thirty years later, while working for AT&T at Bell Labs, she pioneered the technology that is responsible for Voice over Internet Protocol (VoIP) phone systems. Without her, VoIP technology could very well be a forgone experiment, culminating with us stuck using classic PBX phone systems.

As a black girl growing up in 60’s New York City, there was very little privilege afforded to Marian Croak, save for her ingenuity, curiosity, and a supportive family. Despite growing up in a time where women, and especially women of color struggled to find acceptance in their goals and ambition, Marian Croak defied the odds, and not for her own personal gain — but rather to reduce the barrier of entry to quality, affordable communication.


Marian graduated with her Ph.D. in quantitative analysis — otherwise known as data science — as well as social psychology from the University of Southern California, and soon after began working for Bell Labs in 1982.

There, Marian first began working on messaging applications, with the task of determining whether various messaging applications could communicate with each other. It’s important to put into perspective how novel this kind of research was at the time — the earliest form of the internet, known as ARPANET, would not come to full fruition until the next year in 1983.

Coincidentally, the technology that would empower ARPANET to eventually morph into the ubiquitous internet as we know it today was the same technology Marian convinced AT&T to utilize for their VoIP system.

AT&T was busy researching how to leverage a technology that could send voice, data, and video digitally, rather than using a standard phone line. Initially, Bell Labs was leaning towards Asynchronous Transfer Mode (ATM) protocol. This method largely works by coding data packets into uniform sizes to send data from one endpoint to the other.

Marian believed in the power of the technology that gave rise to ARPANET, TCP/IP, and convinced AT&T to abandon ATM in favor of TCP/IP, which provides end-to-end communication by specifying how data should be packetized, addressed, transmitted, routed, and received.

TCP/IP uses four abstraction layers send data: the link layer, the internet layer, the transport layer, and the application layer.

While this technology wasn’t fully fledged at the time, Marion’s expertise convinced AT&T to leverage TCP/IP, and the rest is history. Without her involvement, we would not have the technology that allows services like Skype, FaceTime, or VoIP in general to exist.


Marian wasn’t done inventing new ways for us to use technology, however. Over the course of her 32-year career at AT&T, she filed 200 patents, one of which was the technology that allowed for cellphone users to donate money through text messages.

If you’ve ever donated money to a charity or cause through text, you can thank Marian.

Now, Marian works as the Vice President of Engineering at Google, where she most recently is responsible for making sure AI projects are researched ethically, possibly one of the most important projects of her entire career.

There is one thing for certain; the world would be a much less talkative place without the mind of Marian Croak, and for that, we thank her.

Kate Vinnedge
Kate Vinnedge is Cobb Technologies' Digital Content Manager. A Richmonder since 2010, she is a believer in the power of tech, and has made it her mission to help foster the adoption of secure, smart, and sensible enterprise systems among businesses by introducing advanced tech ideas through the creation of easily-understandable and digestible content. When Kate isn't writing about tech, she is hiking, playing D&D, or working on her very own table-top roleplaying game.