Where the time goes (the four delays, and the buffer that fills)

The long-distance reading, where the round trip grew from 265 ms to 374 ms before a single page was lost. This lesson asks where those extra 109 ms were sitting, and the lab at the end of the story lets you build the place yourself.

Before you start. From How a parcel finds any house on earth you have the picture this lesson stands on: a router is a depot, a packet is a parcel, and every parcel is handed from depot to depot until it reaches the address on it. From Reading a book aloud to America you have the round trip (how long a message takes to reach the far end and its reply to come back) and the sender’s window, which TCP grows until something is lost and then cuts. This lesson takes one round trip apart and asks what it is made of.