Help pllz

1. What are the two fundamental mechanisms to provide reliable transmission? (10 pts) 2. Figure 1 shows timeline of four different scenarios (a). (b). (e) and (d) for the stop-and- wait algorithm. Please explain each scenario and give a solution to solve the problem if there is one [40 pts.] (a) Sender Receiver (c) Sender Receiver ACK (b) Sender Receiver(d) Sende Receiver ACK ACK Fig. 1: Timeline showing four different scenarios for the stop-and-wait algorithm