CompTIA A+® Certification All-In-One For Dummies®, 2nd Edition

1.9. Understanding Communication Methods

Different network devices, such as network cards, support different methods of communication. The three major communication methods in the computer world are simplex, half-duplex, and full-duplex:

• Simplex: A device that supports simplex communication can deliver information in only one direction. Typically, the device can send information but cannot receive information.

• Half-duplex: A device that supports half-duplex communication can deliver information in two directions, but not at the same time. A typical example of a half-duplex device is a walkie-talkie or CB radio, which enables you to send and receive information but not at the same time. When you use a CB radio, you say "Over" to let the person on the other end know that you are done talking and that it is the other person's turn to send information.

• Full-duplex: A device that supports full-duplex communication is one that can send and receive information at the same time. Full-duplex is similar to talking on the phone: You are free to speak and to listen at the same time.

When purchasing networking or other types of devices for your computer, it is important to know whether you are buying a simplex, half-duplex, or full-duplex device to avoid problems later. For example, a musician friend of mine wanted to record his own material on the computer with recording software. After recording the first track, he had a problem recording a second track because his sound card was only a half-duplex ...