If the Internet works by routers handing data to each other down the line, what happens when the data is large? What if we request the 88.5 MB video of The Birth & Death of JavaScript?

We could try to design a network where the 88.5 MB document is sent from the web server to the first router, then to the second, and so on. Unfortunately, that network wouldn't work at Internet scale, or even at intranet scale.

First, computers are finite machines with finite amounts of storage. If a given router has only 88.4 MB of buffer memory available, it simply can't store the 88.5 MB video file. The data will be dropped on the floor and, worse, I'll get no indication. If a router is so busy that it's dropping data, it can't take the time to tell me about dropped data.

Second, computers are unreliable. Sometimes, routing nodes fail. Sometimes, ships' anchors accidentally damage underwater fiber-optic cables, taking out large portions of the Internet.

For these reasons and more, we don't send 88.5 MB messages across the Internet. Instead, we break them down into packets, usually in the neighborhood of 1,400 bytes each. Our video file will be broken into 63,214 or so separate packets for transmission.