David L. Mills, Who Kept the Internet Running on Time, Dies at 85

David L. Mills, an internet pioneer who developed and, for decades, implemented the timekeeping protocol used by financial markets, power grids, satellites and billions of computers to make sure they run simultaneously, earning him a reputation as the internet’s “Father Time,” died on Jan. 17 at his home in Newark, Del. He was 85.

His daughter, Leigh Schnitzler, confirmed the death.

Dr. Mills was among the inner circle of computer scientists who in the 1960s through the ’90s developed Arpanet, a relatively small network of linked computers located at academic and research institutions, and then its globe-spanning successor, the internet.

It was challenging enough to develop the hardware and software needed to connect even a small number of computers. But Dr. Mills and his colleagues recognized that they also had to create the protocols necessary to make sure the devices could communicate accurately.

His focus was time. Every machine has its own internal clock, but a network of devices would need to operate simultaneously, down to the fraction of a millisecond. His answer, first implemented in 1985, was the network time protocol.

The protocol relies on a stratified hierarchy of devices; at the bottom are everyday servers. These regularly ping upward to a smaller number of more powerful servers, which in turn ping upward again, all the way to another small number of powerful servers linked to an array of timekeeping devices like atomic clocks.

Based on a consensus time drawn from these core devices, the “official” time then flows back down the hierarchy. Nestled within the system are algorithms that seek out errors and correct them, down to a tenth of a millisecond.

The process is highly complicated for several reasons: Data moves at different speeds across different types of cables; computers operate faster or slower; and packets of data can get held temporarily along the way at routers, known as store-and-forward switches — all of which required a degree of programming sophistication on Dr. Mills’s part that astonished even other internet pioneers.

“I was always amazed at the fact that he can actually get highly synchronized time out of this store-and-forward system with variable delays and everything else,” Vint Cerf, who helped develop some of the earliest protocols for Arpanet and is now a vice president at Google, said in a phone interview. “But that’s because I didn’t fully appreciate the Einsteinian computations that were being done.”

Dr. Mills, who was a professor at the University of Delaware for much of his career, not only published but also regularly updated the protocol over the next two decades — making him the internet’s semiofficial timekeeper, though he called himself an “internet grease monkey.”

The network time protocol was only one of Dr. Mill’s contributions to the underlying architecture of the internet. He created the fourth version of the internet protocol, essentially its basic playbook, in 1978; it is still the dominant version in use today.

He also created the first modern network router, in the late 1970s, which provided the backbone of NSFnet, a successor to Arpanet that evolved into the modern internet. A fan of quirky names, he called the routers “fuzzballs.”

“It was a sandbox,” he said in a 2004 oral history interview, describing the early days of network programming. “And we essentially were not told what to do. We just were told, ‘Do good deeds.’ But the good deeds were things like develop electronic mail and protocols.”

David Lennox Mills was born on June 3, 1938, in Oakland, Calif. His mother, Adele (Dougherty) Mills, was a pianist, and his father, Alfred, sold gaskets used to prevent leaks in machinery.

David was born with glaucoma, and although a childhood surgery restored some degree of sight in his left eye, he would use oversized computer screens his entire career. He attended a school for the blind in San Mateo, Calif., where a teacher told him his poor sight meant he would never go to college.

He persevered and was accepted to the University of Michigan. There he received bachelor’s degrees in engineering (1960) and engineering mathematics (1961); masters degrees in electrical engineering (1962) and communications science (1964); and a doctorate in computer and communications science (1971).

Computer science was just emerging as a field. It did not fully exist when he arrived at Michigan, and when he submitted his doctoral dissertation over a decade later, it was only the second of its kind ever completed at the university.

He married Beverly Csizmadia in 1965. Along with their daughter, Leigh, she survives him, as do their son, Keith, and his brother, Gregory.

After teaching for two years at the University of Edinburgh, Dr. Mills spent five years at the University of Maryland before moving in 1977 to Comsat, a federally funded corporation created to develop satellite communication systems.

His work at Comsat put him in close contact with Dr. Cerf and others working on Arpanet, which began in 1968 with just four computers at four research institutions, and grew to include about 40 institutions within a decade.

There was little hierarchy among those first researchers; they coordinated their work over an early version of email and made decisions based on rough consensus. Dr. Mills soon attached himself to the question of time because, he later said, no one else was doing it.

In 1986 he moved to the University of Delaware, which by then had become an important East Coast hub for networking research. He took emeritus status in 2008 but continued to teach and conduct research.

Throughout his life, Dr. Mills was an ardent ham radio operator; as a teenager he was in touch with Navy Seabees working in Antarctica and patched them through to their families in the United States.

His clapboard, two-story house in Newark had an enormous antenna array on its roof. On his university website, he joked that “in emergencies, the rooftop antenna can be converted into helicopter rotor blades and lift the house to safety.”