How Does the Internet Work?網際網路怎麼運作？

🔊Your grandfather lives in Boston, and you send him a photo on LINE from Changhua. Less than a second later, his phone buzzes on the other side of the world. The photo did not fly through the air the whole way, and it did not travel in one piece. It was chopped into thousands of small pieces that raced under the Pacific Ocean and were put back together on his phone.

🔊The internet began with a crash. On October 29, 1969, a student at UCLA tried to send the word login to a computer at a research institute about 560 kilometers away. The letters L and O arrived, and then the system crashed. So the first message on the network that grew into the internet was simply LO. In 1974, Vint Cerf and Bob Kahn described a set of rules called TCP/IP, and the network switched to those rules on January 1, 1983. The internet still runs on them today.

🔊The big idea is packets. Your phone cuts your photo into small pieces called packets, each up to about 1,500 bytes, so a three-megabyte photo becomes about 2,000 of them. Every packet carries three things: a piece of the photo, the address where it is going, and its number in the line. Like postcards, the packets travel separately, and each one finds its own way.

🔊Along the way, packets pass through routers, special computers that read the address and send each packet one step closer, like mail sorters at the post office. Messaging apps first send your photo to the company's computers, called servers, which pass it on to your grandfather's phone. Because each router chooses a path on its own, two packets from the same photo may take different roads and arrive out of order. If one is lost, his phone notices the missing number and asks for it again.

🔊To cross the ocean, the packets travel through undersea cables. Almost all data that goes between continents uses these cables, not satellites. In deep water, a cable is about as thick as a garden hose, and inside are glass fibers thinner than a hair that carry the data as flashes of light. Light in glass travels about 200,000 kilometers every second, so even the 12,500 kilometers from Changhua to Boston take only a fraction of a second.

🔊Taiwan is connected to the world by 14 international undersea cables, which come ashore at landing stations in places like Tamsui and Toucheng. Because there are many cables and many routes, the internet can keep working when one breaks. In 2023, when both cables to the Matsu Islands were cut by passing ships, the islands had very slow internet until they were repaired. That is why engineers keep building more paths: the internet works because no single road is the only road.