There are two methods for bringing Wi-Fi to planes. One uses special ground-based cell towers, while the other uses satellites.

But how exactly does Wi-Fi work on planes? One of the biggest providers of inflight internet, Gogo, uses both ground-based towers and satellites around the world, which service airlines including Delta, United, Alaska Airlines and Virgin Air. Here, Steve Nolan, vice president of communications and public relations for Gogo, explains how these services work.

How do cell towers power in-flight internet?

Ground-based cell towers, which was the first method of delivering in-flight Wi-Fi, are similar to the same towers that deliver Wi-Fi to cell phones.

The large towers project wireless service by pointing toward the sky, delivering Wi-Fi to planes flying overhead. In contrast, towers used by wireless providers direct coverage toward the ground. Turning the coverage toward the sky allows airline towers to have a larger coverage area.

“If you think about how a radio wave works, it goes out like a cone,” Nolan said. “So you need many more ground towers because they’re closer to the ground and the beam doesn’t wide out as much. When it points upwards, it widens into a much larger space.”

How do satellites power in-flight internet?

With satellite powered-Wi-Fi, planes connect to the internet using an antenna mounted on top of the plane. Besides using a different frequency than cell towers, satellite-powered service also allows planes to provide faster service and can be used over water.

This new technology has been embraced by more and more airliners. According to Nolan, 1,600 planes are committed to installing Gogo’s satellite technology, though other companies also offer the service.

JetBlue, which became the first airline to offer free high-speed internet on all of its planes in January, has been offering its FlyFi service since 2013. A JetBlue spokesperson said the company uses satellites from companies including ViaSat and Thales for its FlyFi service, which is offered on its flights within the U.S.

Can you use plane Wi-Fi anywhere (including oceans)?

Where you can get Wi-Fi while flying depends on the service your airline uses. For example, Gogo’s air-to-ground technology uses cell towers and only works when above land, according to Nolan. Their satellite Wi-Fi can work overseas, though there can be gaps in coverage. The service also will not work over the North and South poles.

How fast is in-flight Wi-Fi?

In-flight Wi-Fi speeds vary based on the provider and the service used. According to Nolan, Gogo’s air-to-ground service, which utilizes cell towers, gives customers 9 Mbps for the entire aircraft and satellite offerings provide 15 Mbps per person. JetBlue’s FlyFi has speeds ranging between 12 and 20 Mbps per person when within the coverage area, according to a JetBlue spokesperson. In contrast, U.S. internet providers Xfinity and Fios offer internet speeds ranging from 10Mbps to 500 Mbps.