The data transmission mode can be generally divided into three parts. These are: a. Simplex b . Half-Duplex c . Full-Duplex Simplex One-way data flow is called Simplex Maid. In this system, the edge that sends data will not be able to receive edge data and the receiving edge will not be able to send data. For example, data can be transmitted from A to B. But data from B to A cannot be transmitted. Examples: PABX systems , radio , TV general programs. Half-duplex This system has the opportunity to send data from both sides , but it is not possible at the same time. Either side can only receive or transmit data at the same time , but cannot receive and transmit at the same time. Example: Go through walkie-talkies. Full-duplex Full-duplex mode has data exchange system from both directions at the same time. Any edge can receive data when sending data or send data when receiving data. Examples - telephone , mobile phone.