QOS cos dscp map

fightclub34

When does the map actually take place. If i do autoqos on a 3550 that is no ip routing i know the map shows in the config. I want to mark at layer 2 and remark when i go across the wan to dscp. does the map conversion take place on the 3550 or would i need a map on my core switch where the svi resides and wan resides. My guess is the map takes place when you hit a layer 3 boundary.