Consider what needs to happen for frames to be transmitted successfully. Let T represent the frame time. For simplicity, it is assumed that the contention begins at t=0. Then if exactly one node sends during interval t=0 to t=T and no node tries between t=T to t=2T, then the frame will be transmitted successfully. Similarly during all next time intervals t=2nT to t=(2n+1)T, exactly one node sends and during t=(2n+1)T to t=(2n+2)T no node tries to send where n=1,2,3, ... , then the frames are successfully transmitted. But in pure ALOHA, the nodes begin transmission whenever they want to do so without checking that what other nodes are doing at that time. Thus sending frames are independent events, that is, transmission by any particular node neither affects nor is affected by the time of start of transmission by other nodes.