Once all the packets arrive at their destination, they are pasted back together into the original message.
"It's as if a long letter were written on a series of small postcards, and each postcard was mailed separately," Kleinrock said.
Packet-switching replaced a less efficient and less flexible transmission technology used by early telephone companies called circuit-switching, which relied on dedicated connections between two parties.
"When you and I talk over a circuit-switched connection, that connection is totally dedicated to our conversation," Kleinrock explained. "Even if we pause to take a coffee break, the connection is still ours and sits by idly while we are silent."
By contrast, data packets in a packet-switched transmission have multiple routes open to them and will hop on to the one with the least amount of traffic. In this way, no route is idle for long.
No One Owns the Internet
In the years following ARPANET's deployment, other packet-switching networks were created, but they were internal networks that had only limited access to one other.
It wasn't until the mid-1970s that engineers developed a way to merge networks to create the Internet.
In 1984 the domain system that includes .com, .gov, and .edu was established. A decade after that, the first commercial web browser, Netscape, became available.
Today the Internet is accessed by more than a billion users monthly.
Several companies and organizations contribute to its upkeep and operation. But no one owns the Internet, since anyone with access to a computer can create Web content.
"If you put your PC out there and offer a news service or something … then you're considered a part of the Internet," Kleinrock said.
Transformed World
Although it's now hard to imagine life without Facebook, Google, and Wikipedia, the broad appeal of the Internet was something many of its inventors never predicted.
"I am surprised, and totally pleased, at how effective the Internet has been in allowing communities of people to form, communicate, exchange ideas, and enter their daily lives in so many ways," Kleinrock said.
(Related: "Googling Fights Dementia, Study Suggests.")
For the last decade, a team led by the University of Southern California's Cole has been tracking the effect of the Internet on societies around the world.
"When we started in 1999, it was already clear that the Internet was going to transform communications," Cole said.
"What we could never have imagined is that it would transform virtually every element of business and social activity."
Cole predicts that in the future, more people will access the Internet through mobile devices such as the iPhone than via personal computers and laptops.
Currently about four billion people around the world have mobile phones, but only about a billion people use PCs, Cole noted.
"We think the Internet is moving completely toward mobile."
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