This is part of the book "Introduction to Networking" at www.net-intro.com
Now that we can move data across a single link, it's time to figure out how to move it across the country or around the world. To send data from your computer to any of a billion destinations, the data needs to move across multiple hops and across multiple networks. When you travel from your home to a distant destination, you might walk from your home to a bus stop, take a train to the city, take another train to the airport, take a plane to a different airport, take a taxi into the city, then take a train to a smaller town, a bus to an even smaller town, and finally walk from the bus stop to your hotel. A packet also needs to take multiple forms of transportation to reach its destination. For a packet taking its "trip" to another country, the "walk", "bus", "train", and "plane" can be thought of as different link layers like WiFi, Ethernet, fiber optic, and satellite.