See deep packet inspection
nch) The measurement of the resolution of a printer. As the dpi rate doubles, the number of dots within a square inch is quadrupled. Thus, while 100 dpi produces 10,000 dots per square inch, 200 dpi produces 40,000 (see table below). This applies to screens as well, which are measured in pixels per inch (ppi).
Screens Are Getting Denser
Increasingly, screen resolutions are equaling the print density of printers, which is why it is easy to read text on smartphones. For example, a smartphone screen at 300 pixels per inch (ppi) means 300 red, 300 green and 300 blue subpixels per inch (900 dpi). The total dots per square inch (900 squared) is 810,000, which is denser than a 600 dpi printer (see table below). See ppi
and E Ink
DPI Square Inch