I want to install an ethernet jack in an interior wall of one room. I'd like to run the cable up through the wall cavity (so it is hidden) into the crawl space and back down another wall to another jack which would be connected to the network router. I presume this is a pretty basic thing to do but I'm not sure how to access the wall cavity. The walls are covered by a horizontal beam that gives me no clue what is underneath or how high they are.
Should I drill down at the red X(see picture) and feed the cable through, then guess the right spot to drill a hole at the site of proposed jack (coloured green)?
NB: I have been reading this question but it doesn't quite answer mine: How do I run ethernet, speaker wire, and coax through a wall into a crawlspace?