Communications Channels and Directions

One-Way Simplex

This is a service that works in only one direction at a time:  Send or receive. Broadcast television and radio are examples of simplex communications. Simplex communication is rare beyond its entertainment or general alert applications because there are few instances where only one person speaks and everyone else listens.

Two-Way Alternating (Half Duplex)

The most familiar form of half duplex is two-way citizen’s band and police radio communications, where only one person at a time may speak while the other listens and responds after the former speaker releases his “talk” button.  Half duplex is useful when bandwidth limits the analog information that can be transmitted.

Because one communicating unit must wait for the parity signal of the other before responding, most computer and communication applications run in half duplex format. Digital transmission is such an efficient information carrier that any lags caused by the format are not noticeable to human beings.

Two-Way Simultaneous (Duplex or Full Duplex)

In full duplex transmission, the available bandwidth of the transmission medium is divided into upstream and downstream portions. The proportion of this division is determined by the relative need for upstream and downstream capacity. Devices working in full duplex can send and receive information simultaneously.  The most familiar example of full duplex transmission is a simple telephone conversation:  Each party can hear the other at all times, even while speaking.