Do we include Transmission delay in Round trip time?
Suppose you have two computers (A and B) both connected to a switch with cut-through forwarding. When you are interested about RTT between computer A and computer B, you'll omit transmission delay, because the switch transmits the frame to B as it arrives from A, so transmission delay is not significant. Now, suppose that our switch uses store-forward, in this case, when the frame arrives, the switch will first store it completely, and then sends it to B, so we have to deal with transmission delay.