# Talk:Simplex communication

## Reason for ANSI standard?

Back in the day (ever since Edison's patent at least), a telephone was a single circuit, used to send in both directions, but only one way at a time. That's just the way things worked. When cabling was developed that allowed traffic in both directions at the same time, that was called duplex, and the old way was referred to as simplex.

Given that duplex has a path always open in each direction, half of that would be a path always open in one direction. Assuming the words mean anything, that would seem to be the definition of half-duplex that makes sense.

A source I trust says that IBM got the definitions of "simplex" and "half-duplex" backwards in one of their glossaries, and that glossary was adopted as the standard. Of course most web sites now parrot the ANSI standard point of view. Is there any good reason other than a mistake behind the ANSI version of the definition? Dpv 15:48, 12 May 2006 (UTC) 1 . Simplex(One way always) like a broadcast radio station. 2 . Simplex(One way at a time) like two way radio with one frequency 3 . Half duplex(One way at a time)like two way radio with two frequencies and 4 . Full duplex two way simultaneously with two frequencies.

```—Preceding unsigned comment added by 212.70.33.213 (talk) 11:13, 29 March 2010 (UTC)
```

## dual-simplex?

I'm looking for an exact definition of dual-simplex, which probably should be mentioned on this page. I think that I know how it relates to simplex and duplex, but it would be great to have someone who knows for sure add it in explicitly. Cashannon 16:22, 6 June 2007 (UTC). probably you are talking about simplex with one frequency. Four categories are as follows: 1 . Simplex  :One freq-One way always like radio broadcast. 2 . Simplex-dual:One frequency, two way but one at a time. 3 . Half duplex: two frequencies, two way but one at a time and 4 . Full duplex: two frequencies both way simultaneously.

## Clarify

"In both cases, the other definition is referred to as half duplex."

What does this mean? I see two definitions of "Simplex" the ITU-T definition and the ANSI definition. So do ITU-T and ANSI define "half duplex" as well? Egriffin 20:20, 30 November 2007 (UTC)

I don't know whether the official definitions address that point but hope my little addition of last week made the two usages a bit clearer. Jim.henderson (talk) 04:28, 12 December 2007 (UTC)

122.168.214.130 (talk) 20:27, 4 September 2008 (UTC)Acctually the simplex is used for one way communication at one time while the duplex can communicate another at other instant.

I am unable to find an ITU-T definition of simplex that is equivalent to half-duplex. See, for example, this page : Query Definitions.

This appears to be consistent with the definition attributed to ANSI.

ITU-T also appear to have a definition for duplex (which matches my understanding of full-duplex as capable of simultaneous transmission in two directions) and of half-duplex Query Definitions

The only area of confusion is thus the use of the word duplex vs full-duplex. There is no actual conflict.

81.105.8.110 (talk) 11:00, 16 December 2009 (UTC)