Reply by Howard Henry Schlunder●October 27, 20052005-10-27
"Paul Burke" <paul@scazon.com> wrote in message
news:3s9cbqFmihsjU1@individual.net...
> Has anyone tried this- single twisted pair 100 base T/2? It would appear
> at first sight to be possible, by connecting the ethernet transformers as
> a hybrid and using half- duplex.
>
> It's for an application that uses ethernet internally, at >10Mb rate, but
> doesn't need the full 100Mb bandwidth, and it would be useful to lose a
> pair in the internal wiring.
>
> paul Burke
First of all: please do not multipost. I see that this message appears in
sci.electronics.design, but without searching for all copies of your
message, it
is impossible to tell if someone has answered your question correctly or
not. It's a big waste of everyone's time. Crosspost if you wish, but avoid
multiposting.
Unlike the other two responses that you've received so far, which are not
particularly negative, Fast Ethernet on only two wires should definitely not
work. In 100Base-TX, the transmitters are constantly transmitting a signal,
even if your application does not produce any frames. This idle state
transmission is done so that the receiving PHY does not lose RX clock
snychronization. This differs from 10Base-T where data is manchester
encoded and thus incorporates a clock with the data. Although it's unclear
to me what you mean by a hybrid Ethernet transformer configuration, I would
expect that any simple scheme which reduces you down to one wire pair would
result in a never-ending collision situation. In all probability, the PHYs
wouldn't even link up.
As far as I know, 100Mbps Ethernet has never existed on coax or any 2 wire
scheme. Briefly looking at 802.3-2002, it appears that it only exists on 2
pairs of Category 5 copper (100Base-TX), 4 pairs of Category 3 copper
(100Base-T4), or 2 optical fibers (100Base-FX).
Reply by Paul Burke●October 26, 20052005-10-26
Has anyone tried this- single twisted pair 100 base T/2? It would appear
at first sight to be possible, by connecting the ethernet transformers
as a hybrid and using half- duplex.
It's for an application that uses ethernet internally, at >10Mb rate,
but doesn't need the full 100Mb bandwidth, and it would be useful to
lose a pair in the internal wiring.
Paul Burke