The 5-4-3 rule is something that engineers use to keep internet networks running smoothly. It's a way of making sure networks don't get too over-crowded and too slow.
Usually, when you send computer data over the internet, it goes in different "packages" of information. Sometimes, too many of these packages arrive at the same time, and if that happens, it can slow down the internet connection.
The 5-4-3 rule is a way to prevent this from happening. It means that when the data is traveling between certain devices, there can only be a certain number of packages allowed.
The numbers in the 5-4-3 rule represent how many packages of data are allowed at different times. First, only 5 packages can arrive at once. Then, after those 5 packages arrive, only 4 more packages can arrive until the five packages before them have finished sending. Finally, only 3 more packages can arrive until the four packages before them have finished sending.
The 5-4-3 rule prevents too many packages from arriving at once which means your internet does not get slow.