# Talk:Duplex (telecommunications)

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## Completely omitted terms, and unclarity

The term "diplex" has been completely ommited from this and related articles.
1) In a "simplex" system, only one transmitter can send on the channel at a time.
2) In a "diplex" system, two transmitters can send on the channel at a time.
3) In a "multiplex" system, multiple (three or more) transmitters can send on the channel at a time.

The abbreviation "TDD" cannot be used for "time division duplexing", because in the United States, "TDD" already means "Telecommunications Devices for the Deaf". I dislike it when people try to give duplicate meanings to acronyms. For example, "USA" always means the "United States of America", and there is no confusion, and likewise, "U.K." always means the "United Kingdom".74.163.48.102 (talk) 03:37, 1 October 2008 (UTC)

### Don't argue about the terms

It doesn't make any sense to discuss about which term came first, or whether "two times half-duplex equals full-duplex". These terms are historical ones that came up as the need arose, and not through some sort of a rational system. They just didn't - and we have the historical terms and continue to use them.74.163.48.102 (talk) 03:44, 1 October 2008 (UTC)

## Simplex vs. Half-Duplex

I know that the article follows tha ANSI standard. Is there any documentation of how that came to be the standard? There are a couple of confusing points:

1. Using the road analogy, everyone agrees that (full) duplex corresponds to a two-lane road, with traffic flowing in either direction, each in its own lane. Half of that would seem to be one lane travelling only in one direction.
2. Similarly, two of what ANSI calls half-duplex gets you full-duplex plus a lot of overhead for managing the direction of traffic in either direction in either lane. When does two times a half equal more than a whole? In duplex communication, I guess. Maybe we could call the result double-half-duplex and confuse everyone?
3. Before duplex communication was invented, people used one line to talk to each other (say on a telegraph). It seems odd that such a system would be called half-duplex, when presumably that was just the way it is prior to duplex.
4. Nobody that did not have a duplex telegraph in mind is likely to have invented a one-way circuit, so does that mean simplex requires duplex, but half-duplex came along independently and first?

If it is possible to document why the decision was made to make the current naming the standard, it might help inquiring minds make sense of the situation. Dpv 15:15, 8 June 2006 (UTC)

Hm, all my education in electronics has always taught me the ANSI spec.
To me, "Dup-" as in "Duplex" means two. Probably why "(full) Duplex" means two-way communication. "Simp-" as in "Simplex" means simple, as in lowest working system, i.e. a one-way broadcast like TV, AM radio stations, etc. Certainly adding traffic management systems and controlling the flow over a single channel is not "simple".
"Half-Duplex" still contains the "dup-" part, so to me it means its still two-way, albeit over one channel with switching.
I don’t agree that two half-duplex channels give you full-duplex. As the entire connection (both channels) can be switched to the same direction, then to me this is simply a wider bandwidth half-duplex channel. Assuming each channel had a 50 Mbit bandwidth, you then have a 100 Mbit half-duplex system, that can transfer 100 Mbit at a time, either up or down or a combination of the two with the proviso that one can't exceed 50 Mbit while the other is happening.
Whether it is done by allocating the available channels to different directions, and switching these as needed or allocating the same channel to different directions via a TDMA protocol, then its still a half-duplex system to me. Bonding multiple half-duplex systems just gives you a finer granularity than an 'up/down' system
Calling a one-way system like TV/radio "half-duplex" to me doesn't sound right. "Uniplex" maybe?? :/
A clear term for one-way already exists and is in use: "simplex". There is no need to invent another.
--87.127.25.131 07:28, 17 June 2006 (UTC)

I know that most people are trained according to the current standards, and once trained they tend to think what they were taught is logical. My question is how the standard came to be the way it is now. It seems odd that two half-duplex don't make a full-duplex. It seems odd that the way telegraphs worked before anyone had duplex is now called half-duplex. But I know standards don't make sense to everyone all the time. (Does anyone really use their favorite term for one-way only communication, whether half-duplex, or simplex, for broadcast radio? I would normally only think of it for something like a telegraph wire with a Morse-code key on only one end and a buzzer only on the other end. "Broadcast" is a good enough term for the radio example.) I really want to know if we can explain the current terminology with documentation of how it came to be the standard. Dpv 11:48, 17 June 2006 (UTC)

"These terms also apply to early PC sound cards, however almost all are now full-duplex." - is it really still possible to buy a half-duplex PC sound card?

## Echo cancellation

Shouldn't echo cancellation (as used by V32, etc) be mentioned here, or am I misunderstanding the page? (I can add it, I just want to be sure this page isn't intended to be specific to, say, radio technologies or something.) Squiggleslash 23:13, 2 January 2007 (UTC)

## Ethernet example

Full-duplex ethernet schemes are more varied than the example given in this article. Below are some methods used to achieve full-duplex operation:

10BASE-T: two simplex twisted pairs, one in each direction.
100BASE-TX: two simplex twisted pairs, one in each direction.
100BASE-T4 (rare): four simplex twisted pairs, one in each direction and two subject to negotiation.
100BASE-T2 (rare): two duplex twisted pairs with echo cancellation.
1000BASE-T: four duplex twisted pairs with echo cancellation.
1000BASE-TX (rare): two simplex twisted pairs, one in each direction.

That's just for ethernet over twisted pairs. Some of the optical standards use wavelength-division multiplexing for full-duplex over a single fiber. There's weird older stuff like 10BROAD-36, too. —Ryan (talk) 20:02, 18 October 2009 (UTC)

## Semi-Duplex Missing?

Why is the popular Semi-Duplex missing in this article? — Preceding unsigned comment added by 108.183.84.89 (talk) 02:41, 8 August 2013 (UTC)