round-trip time (RTT) is the length of time it takes for a signal to be sent plus the length of time it takes for an acknowledgment of that signal to be received. This time delay therefore consists of the propagation times between the two points of a signal.
it should be rtt= 2*tp+tt
FULL DUPLEX = means the signals can be sent in both direction at same time...without any problem for ex= mobile networks we talk on mobile and both parties can speak at same time
HALF DUPLEX = means the signals can be sent in both direction but one at a time...for ex- railway networks on a railway track trains can travel in both direction but one at a time//////or walky talky is also an example
SIMPLEX means the signals can travel in only one direction for ex- t.v,,,,radio