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Re: OT: Strange network cable problem



Alon Altman wrote:

>On Thu, 20 Sep 2001, guy keren wrote:
>
>>On Wed, 19 Sep 2001, Alon Altman wrote:
>>
>>>I've recently purchased a 20m crossed CAT5 network cable to connect
>>>between two 10/100 CNET PRO200 LAN cards (http://www.cnet.com.tw/). It turns
>>>out that the cable transferrs data only in one direction (conclusion from
>>>tcpdump output of ARP attempts). I have elctrically tested the cable and it
>>>seems that the conncetions are OK and there are no shorts.
>>>
>>apprently, you've got the wiring set up incorrectly. as far as i know,
>>data sending and data receiving is not done on the same wire. one is used
>>for 'send' and one for 'receive'.
>>
>>find a diagram of how a proper cable should be wired, and compare it with
>>the cable you've got. most like something there was improperly wired.
>>
>
>  The cable is wired correctly (I have another one with exactly the same
>wiring that works).
>
>  What can it be?
>
>  Alon
>
If the other cable works with the exact same machines and configuration, 
your cable is bad.

Please bear in mind that ethernet connection requires more than just the 
electrical connectivity and the right resistance (which a ohm-meter will 
tell you). You also need good internal seperation (connect the right 
twisted pairs), and frequency response. That's the reason good cat-5 
cable checkers are expensive. I will add that I don't believe this is 
your problem, though, as that would cause problems occasionally, not 
consistantly.

Just for general info, here are the wiring for cross cable connections. 
The order of the numbers I give are because each two must come from the 
same pair (marked with the same color, one straight, one striped with 
white):
1 -> 3
2 -> 6
3 -> 1
6 -> 2

all the rest (if you insist on connecting them) should be connected to 
the same number (i.e. - 4->4). I don't know the pairs allocation, 
though, nor when they are used.

            Shachar




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