Midterm

  Design a sliding window protocol under the following assumptions: Data messages from sender to receiver are not lost. Ack messages from receiver to sender may get lost. Timeouts are premature and window size may be greater than 1. Note that it is important that the protocol be as efficient as possible. You should choose between whether to use Go-back-N or selective retransmission, sender or receiver timeouts, and give reasons.

Design a protocol with four processes (A,B,C,D) to control traffic light at a 4-way intersection. Processes A, B, C, D control the light facing the north, south, east and west respectively. The light can be in three states: red, yellow and green. The states transition in a cyclic manner from red  green  yellow  red. If A or B is Green, then C and D must be red (and vice versa). A and B can be green at the same time, and C and D can be green at the same time.