Mesmo depois de ter cursado Redes de Computadores e Sistemas Distribuídos, eis uma empreitada que nunca passou pela minha cabeça. Simplesmente extraordinário!
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Space exploration is hard, not least because of how difficult it is to communicate. Astronauts need to talk to mission control, ideally by video communication, and space vehicles need to send back data they gather, preferably at high speed and with little delay as possible. At first, space missions designed and carried their own distinct communications systems; that worked well enough, but it wasn’t exactly a paragon of efficiency. Then one day in 1998, the internet pioneer Vinton Cerf imagined a network that could offer a richer capacity to serve the growing number of people and vehicles in space. The dream of an interplanetary internet was born.
But extending the internet to space isn’t just a matter of installing Wi-Fi on rockets. Scientists have novel obstacles to contend with: The distances involved are astronomical, and planets move around, potentially blocking signals. Anyone on Earth who wants to send a message to someone or something on another planet must contend with often-disrupted communication paths.
“We started doing the math for the [internet standards] which had worked perfectly well here on Earth. However, the speed of light was too slow,” Cerf said of his early work with colleagues in the InterPlanetary Networking Special Interest Group. Overcoming that problem would be a major undertaking, but this American computer scientist and former Stanford professor is used to helping make big things happen.
Decades ago, Cerf and Robert Kahn — the “fathers of the internet” — developed the architecture and protocol suite for the terrestrial internet known as Transmission Control Protocol/Internet Protocol (TCP/IP). Anyone who has ever surfed the web, sent an email, or downloaded an app has them to thank, though Cerf is quick to push back on the fancy title. “A lot of people contributed to the creation of the internet,” he said in his usual measured voice.
"TCP/IP doesn’t work at interplanetary distances. So we designed a set of protocols that do."
To transfer data on Earth’s internet, TCP/IP requires a complete end-to-end path of routers that forward packets of information through links such as copper or fiber optic cables, or cellular data networks. Cerf and Kahn did not design the internet to store data, partly because memory was too expensive in the early 1970s. So if a link along a path breaks, a router discards the packet and subsequently resends it from the source. This works well in Earth’s low-delay and high-connectivity environment. However, networks in space are more prone to disruptions, requiring a different approach.
In 2003, Cerf and a small team of researchers introduced bundle protocols. Bundling is a disruption/delay-tolerant networking (DTN) protocol with the ability to take the internet (literally) out of this world. Like the protocols that underlie Earth’s internet, bundling is packet-switched. This means that packets of data travel from source to destination by way of routers that switch the direction in which the data moves along the network’s path. However, bundling has properties the terrestrial internet does not have, such as nodes that can store information.
A data packet traveling from Earth to Jupiter might, for example, go through a relay on Mars, Cerf explained. However, when the packet arrives at the relay, some 40 million miles into the 400-million-mile journey, Mars may not be oriented properly to send the packet on to Jupiter. “Why throw the information away, instead of hanging on to it until Jupiter shows up?” Cerf said. This store-and-forward feature allows bundles to navigate toward their destinations one hop at a time, despite large disruptions and delays. His most recent paper on the subject highlights the applicability of Loon SDN — a technology capable of managing a network that moves around in the sky — to NASA’s next-generation space communications architecture.
Beyond the interplanetary internet, Cerf, now in his 70s, also focuses on his day job as chief internet evangelist for Google. This is a fancy title he embraces, brimming with a preacher’s eagerness to spread the internet, via global policy development, to the billions of people around the world without it. He is at once ambitious with serious ideas, while maintaining a playful side. Even though he typically sports a well-trimmed beard and three-piece suit — some say he’s the inspiration for the god-like Architect in the Matrix movies — he once started a keynote speech by unbuttoning his jacket and shirt, Superman-style, to reveal a T-shirt that read: “I P ON EVERYTHING!”
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