On Wed, 22 Dec 1999, Paul Lee wrote:
> Hello,
>
> I have two computers with different Ethernet cards, DEC tulip & 3com 10BaseT.
> When I talk to a vender, they say I need to use cross-over cable since my network
> doesn't have hop. But being a newbie, I don't know much about anything.
> I got some cable but it looks like it's not working (maybe setup is fault).
> It says "CAT 5" and has only 4 small wires in inside.
> Is it correct cable? Any help will be greatly appreciated.
>
> Thanks,
> Paul
The standard UTP cable has 8 wires, but 4 are actually used for 10BASET
Ethernet, with an RJ-45 connector (8-pin 'giant phone jack'). If you hold
the RJ-45 connector facing you with the lock tab on the top, then the pins
are numbered 1 to 8 from left to right. The pin usage is as follows:
1 Transmit +
2 Transmit -
3 Receive +
4 Not used
5 Not used
6 Receive -
7 Not used
8 Not used
Differential signal pairs must be on the same twisted pair, so pins 1 and
2 must be a pair, and pins 3 and 6 must be a pair. Normal mapping is
straignt through pin-to-pin:
1 ------ 1, 2 ------ 2, 3 ------ 3, 6 ------ 6
The crossover function is accomplished by simply wiring the receive pins
to transmit pins:
1 ------ 3, 2 ------ 6, 3 ------ 1, 6 ------ 2
For example, you may have on side one Pin 1 - Blue wire, Pin 2 -
Blue-white wire, Pin 3 - Green wire, Pin 6 - Green-white wire. Then on
side two you will have Pin 1 - Green wire, Pin 2 - Green-white wire, Pin 3
- Blue wire, Pin 6 - Blue-white wire.
All this info can be found in the Ethernet-HOWTO. I suggest you read it
carefully.
HTH
alex
