On Jan 21, 2007, at 21:59, David Schulz wrote:

hey, sure, of course i have checked the cat5 first, but it is clearly not the cable. id say it is as ted has written. what i would like to know now is how exactly happens this "hardware incompatibility"?

The interface chips use a very low level "protocol" to identify the rates and modes being used by the other end. Those are dependent on voltage thresholds which sometimes are not as accurate as one would like. Components age and tolerances change which can cause the two ends to get out of sync with each other. The interface specifications also tend to change a bit over time. I don't have the exact specs for ethernet, but the same issue arose many years ago with RS-232 devices. The original specification had a threshold voltage of around 20 volts. For line drivers with 25-28 volt sources it worked great. But, 25 volts is somewhat difficult in many situations and people started fudging using 12 V sources which would work with many of the drivers that actually used a 10 V threshold. Those devices would interface with some, but not all of the older devices. Ethernet has undergone a number of changes from the original RG-8 cabling to today.
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