[Computer Network Course]

7. (Problems with solving exposed node problem) Consider the wireless network in Figure1. Node A performs CSMA/CA procedure proposed by MACAW, in other words RTS-CTS-DATA-ACK sequence for transmission. Sup pose node B has just received RTS from node A and found out that A tries to transmit to node C, but did not hear CTS from node C. Node B concluded that he became an exposed node and decides to transmit data to node D. (a) Node B initiates RTS-CTS-DATA-ACK sequence with node D, at the same moment as A starts to transmit data packet. What is the potential problem with node Bs attempt? (Hint: Suppose node A is transmitting a large packet.) Figure 2: B is an exposed node. b) Instead of MACAW procedure, node B starts DATA-ACK sequence (CSMA-CA in weaker sense) for trans- mission to node D, at the same moment as A finishes transmitting data packet. What is the potential problem with node Bs attempt? (Hint: Suppose node B is transmitting a large packet.)