On Nov 8, 2007, at 10:35 PM, John Barrett wrote:
> A repeater is NOT full duplex.. it is not simultaneously processing
> completely separate audio streams in and out.. it is processing the
> SAME audio in and out. There is only ONE audio path – full duplex
> requires TWO. Telephones accomplish this by modulating both audio
> signals on a common “carrier” (the DC power provided by the telco),
> modems do it by using different tone frequencies for send and
> receive.. essentially half duplex, but coerced into being full
> duplex by the behavior of the telephone line. The modems accomplish
> this by negotiating which modem will use which frequencies (hence
> all the V## protocols.. they define how the modems negotiate)
>
> A repeater is NOT bidirectional – audio streams flow in only one
> direction, from sender to reciever
>
> From this point of view the repeater is a filter in a half duplex
> link. The only reason a repeater uses 2 frequencies is because you
> cannot transmit on the same frequency as you receive..
>
> Full duplex direct (non-repeater) RF links require 2 frequencies..
> one transmit for user A, and one transmit for user B.. this is a
> true example of full duplex.. both streams are completely
> independent, and have no influence on the other except through
> “processing” at the end points, human, computer, or otherwise.
>
> You could accomplish an apparent full duplex repeater link in RF
> using 3 frequencies… 2 for input, one for output, and mix the
> inputs. The only problem is the 2 users have to agree which input
> they will use (oooo shades of modem negotiation here !!)… a Party
> Line, or Conference Call would require one input per user.. In each
> of these cases, all users listen to the same output.
>
John, you've hit on what I was struggling to describe...
Coming from the datacomm world I see "full-duplex" as both senders of
information can send separate information at the same time... without
interrupting each other.
But Joe's dictionary definition of full-duplex is also technically
correct, just applied differently.
(We need better terminology to really describe these differences
concisely.)
--
Nate Duehr, WY0X
[EMAIL PROTECTED]
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