数据流 Direction of data Mainframe Monitor a.Simplex Direction of data at time 1 Station Station Direction of data at time 2 b.Half-duplex Direction of data all the time Station Station c.Full-duplex 1.6 图1.2 数据流(a.单工，b.半双工，c.全双工)1.6 图1.2 数据流(a.单工, b.半双工, c.全双工) 数据流