100 Base 2(?) anyone?

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

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Paul Burke
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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).

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Howard Henry Schlunder

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