This might be basic, but I don't know the answer... Given a router and a client, both having 2.4 (slower, more range) and 5.0 (faster, less range) frequency radios (and both named with the same SSID on the router), what determines which frequency gets used by the pair? The client or the router? Based on what? (Signal strength? Data throughput?)

I was thinking router, but I was told it was the client (by a system integration "Engineer" here at my employer.)