In memoriam: David L Mills, who kept the Internet running on time
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
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 recognised 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 synchronised 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 semi-official 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.