I noticed European hockey leagues use a promotion/relegation system. But how do farm teams work?

How do they call up/send down players?
Answers

Leafsfan29-Embrace the drought!

Think soccer. They have youth/development teams for younger players in lieu of junior leagues and universities that do their own thing.

Bob

The player either gets called up to the team on the higher level, or gets sent down to a team on a lower level, many countries use a system like this in soccer, MLB teams have and all or almost all NHL teams have a minor league affiliate team and the NBA has the Developmental or D league.