Figure 1 shows a woman calling a man on the phone and each is asking the other a question at the same time.  Neither one can understand the other.  This represents access method. Figure 2 shows the woman asking if the man can hear her, and the man doesn’t answer because he cannot understand the woman.  This represents the need for flow control. Figure 3 shows the man not answering her, so she repeats the question.  This is representing the response timeout of a communication.