AT&T 7200 series, 7500 series, 7100 series manual ∙ ∙ ∙, Simplex vs. Half-Duplex vs. Full-Duplex

DATA CONNECTIVITY — AN OVERVIEW 7-5

_______________________________________________________________________________________

_

ASYNCHRONOUS (START/STOP) TRANSMISSION

ONE CHARACTER (7 OR 8 BITS) AT A TIME

ST 1 2 3 4 5 6 7 P SP IDLE

ST = START, P = PARITY, SP = STOP

ST

1

2

∙ ∙ ∙

SYNCHRONOUS TRANSMISSION

SYN	SYN	SOH			TEXT	ETX	BCC
				BLOCK OF
			CHARACTERS

Figure 7-2.Synchronous vs. Asynchronous Communication

Protocol converters and terminal emulators can convert communications between synchronous and asynchronous. See chapter 8 for an explanation of how these devices and programs are used to connect dissimilar devices.

Simplex vs. Half-Duplex vs. Full-Duplex

The terms simplex, half-duplex, and full-duplexdescribe the mode of DTE operation (see figure 7-3).

∙Simplex communication occurs in one direction only. No communication ever occurs in the opposite direction.

Because simplex communication only occurs in one direction, its application is limited to monitoring and broadcast devices, like burglar alarms and telemetric collars for wildlife.

∙Half-duplexcommunication occurs in one direction at a time over a communications link. Although data can be sent in both directions, half-duplex links cannot communicate in both directions simultaneously.

∙Full-duplexcommunication uses a transmission link to communicate in both directions at the same time.

Note that communication lines are usually 4-wire links that are capable of full-duplex communication. The DTE dictates whether the link is for full-duplex or half-duplex communication.

In a communications path, the DCEs supervise communication along the link. The DCEs should be set for the mode of operation the DTEs expect.