AUI crossover?

[Paul Koning]

>>>>> "John" == John Allain <allain at panix.com> writes:

 John> I am playing around with networking again, and realized I have
 John> a lot of AUI transcievers of different types, and only one AUI
 John> hub.  Question is, can two AUI-male connecting converters be
 John> connected together with an appropriate cabelling, like you can
 John> do with RJ45/10bT, or must a person always use a hub/repeater
 John> box?

 John> here's my notes, looks doable any problems?  3 TX+ 5 RX+ 6 +12v
 John> return 10 TX- 12 RX- 13 +12v

You missed the Collision wires, and therein lies the trouble.

There are two issues. 

One is that an AUI based Ethernet was half duplex (just like
10Base2).  If you just cross over rx/tx you have a full duplex setup.
If the NIC is full duplex capable that MAY work, but depending on the
NIC it may not be full duplex capable.

The other issue is that 8u02.3 compliant NICs will expect the
collision signal to assert briefly after each packet.  That is the
Collision Test (SQE test, see 802.3 section 8.2.2.2.4).  DEC NICs, for
example, generally implement this.  I *think* this is a warning, so if
the driver doesn't treat it as an error you'll probably be ok.

You said you have lots of transceivers.  So why do you want crossover?
Just hook the AUIs to their coax and wire up a classic Ethernet that
way.  Or did you mean AUI based NICs?  (For that matter, what's an
"AUI Hub"?  I know AUI repeaters, and I know AUI transceivers.)

     paul