Link controller round-trip time and line quality calculations

Dears, For the Link controller, how it determine the Using round-trip time and line quality:

I think for the round trip time, when it receives an internal user request to go to (for ex yahoo.com) it will send the tcp sync out of the two links, and check which one will send back the sync ack first

for the line quality i think that it will check for the dropped packet and how many time it does the tcp transmission.