7. (10 points) The diagram at right shows a WIFI network with an access point, X and hosts B and C. The large circles indicate the coverage areas of the three hosts. The coverage area for X is not shown, but you may assume that it includes all three hosts. Assume RTS/CTS are not used. Suppose X is transmitting a packet at time 0 and finishes sending it at time 100 s. Also, B gets a packet at time 70 that takes 200 s and is assigned a backoff timer of 50. C gets a packet at time 90 that takes 150 s and is assigned a backoff timer of 150. For each of the three, what time do they start sending their packets? You may ignore the inter-frame spacing and the time required for acks. Of the three packets sent, which are successfully delivered on the first attempt? For each packet that is not successfully delivered on the first attempt, approximately when does the sending host learn that the packet was lost and must be sent again? Now, suppose RTS/CTS is enabled. In this case, approximately when does each host send its data packet? You may assume that the time needed to send RTS, CTS and ACK packets is negligible. (x)