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On April 6, something known as the GPS rollover, a cousin to the dreaded Y2K bug, mostly came and went, as businesses and government agencies around the world heeded warnings and made software or hardware updates in advance.
But in New York, something went wrong — and city officials seem to not want anyone to know.
At 7:59 p.m. EDT on Saturday, the centralized Global Positioning System that connects to devices and computer networks around the world underwent a long-anticipated calendar reset. Known as a rollover, the reset knocked out a major wireless communications network used by New York City agencies.
The shutdown of the network, known as the New York City Wireless Network, or NYCWiN, has waylaid numerous city tasks and functions, including the collection and transmission of information from some Police Department license plate readers.
The network also allows the Department of Transportation to program traffic lights, and helps offices of far-flung agencies such as the sanitation and parks departments stay connected, among other uses.
There has been no public disclosure that NYCWiN, a $500 million network built for the city by Northrop Grumman, was offline and remains so, even as workers are trying to restore it.
City officials tried to downplay the outage when first asked about it on Monday, speaking of it as though it were a routine maintenance issue.
“The city is in the process of upgrading some components of our private wireless network,” Stephanie Raphael, a spokeswoman for the Department of Information Technology and Telecommunications, said in an email on Monday. She referred to the glitch as a “brief software installation period.”
By Tuesday, the agency acknowledged the network outage, but stressed in an emailed statement that “no critical public safety systems are affected.”
Ms. Raphael admitted that technicians have been unable to get the network back up and running, adding, “We’re working overtime to update the network and bring all of it back online.”
The outage has raised questions about whether the city had taken appropriate measures to prepare the network for the GPS rollover.
Ms. Raphael did not respond to questions about what the city had done to prepare for the rollover; she said that the city pays $37 million a year to Northrop Grumman to maintain and operate NYCWiN. A Northrop Grumman spokesman referred all questions to the city.
“If the city’s paying $40 million a year to maintain software infrastructure, first, when it goes down, the Council and the public should know about it,” said Councilman Brad Lander of Brooklyn, who learned about the outage when he was told of it by The New York Times.
“And two, if it’s mission critical, then it should be clear: the effort to get it up and running, and account for those things that are lost.”
Mr. Lander, who sits on the Council’s technology committee, said that the committee might hold a hearing to look into the cause of the outage and how it was handled.
Many computerized systems use the Global Positioning System as a timekeeper because it is convenient and easy to connect to, according to a Department of Homeland Security advisory about the reset posted on the agency’s website.
Approximately every 20 years, the GPS needs to reset the way it keeps track of weeks — and Saturday, April 6, was the date selected for the most recent reset. The reset also came with an improvement in timekeeping that means the next rollover will not be needed for about 157 years.
According to Homeland Security, which first issued a notice about the rollover a year ago, newer systems were considered to be safe but older equipment might need updates to software or hardware.
Ms. Raphael would not provide a list of agencies that use the system.
But a Department of Information Technology and Telecommunications alert that went out on Saturday showed that 38 Police Department license plate readers had gone down. The city maintains a system of license plate readers mounted at fixed locations and on patrol cars, which it uses to scan license plates. That has helped it in routine crime fighting, such as finding stolen vehicles, and its antiterrorism work.
Phil Walzak, a police spokesman, said the department had hundreds of license plate readers, most of which did not rely on the NYCWiN system. He said that patrol cars with readers mounted on them were stationed at key locations affected by the outage and that “the N.Y.P.D. has not experienced disruption to operations, investigations or services.”
Saturday’s alert also reported that 12,389 traffic-signal controllers were down. According to the information technology agency’s website, the Transportation Department’s Traffic Management Center uses the network “to centrally monitor and wirelessly program traffic patterns during rush hours, special events and emergencies.”
While traffic signals continued to operate normally, a city official who was not authorized to speak publicly about the outage and asked not to be named, said that there was concern that as they remained disconnected, the timing of individual signals could drift slightly and they could eventually come out of sync with one another.
The disruption also affected the transportation department’s Real Time Traffic Information webpage, where people can look at the video feeds from hundreds of cameras posted around the city. The webpage showed that many cameras were not working on Wednesday.
The alert indicated there were also disruptions to the city payroll system, known as CityTime, and systems used by the departments of health, sanitation and parks.
The wireless network was intended to fill a gap in the ability of city agencies to communicate with each other and access information, that was exposed during the 2001 terror attack on the World Trade Center, when police and fire department officials could not talk to one another because their radios used different frequencies.