There are four computers A, B, C, and D connected to the communication link of a LAN. A and D are the farthest computers and are located 6Km apart. The network uses CSMA/CD for the communication among the computers and the signals are known to travel at 240000Km/s and the transmission rate being 200 Mbps on the link.

a) Assume at t=0 all computers detect that the link is free and computer A starts sending a packet of ize 1250 Bytes on the link. Calculate up to what time, computer D may mistakenly assume that the link is free and start sending its packet on the link? Please show your work.

b) In part (a) assume computer D starts sending its packet at t=30s (1 = 1 millionth). Is it following the communication protocol or not? Elaborate.

c) In part (a) assume computer D starts sending a 500-Byte packet at t=20s. Draw a Space-Time diagram for this communication case, calculate and show the important times, and calculate at what time willl computer D detect the collision (if any). Repeat the calculations for computer A.