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Many Ethernet devices predating the ubiquity of RJ45 transceivers had DB15 "AUI" ports. One is ordinarily expected to attach a transceiver for either coaxial or twisted-pair Ethernet.

Is it possible to cross-connect two AUI ports using an appropriately short cable that crosses the data send/receive pins, without using transceivers?

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Welcome to 1991! – Mark Henderson Apr 2 '12 at 3:54
@MarkHenderson Seems I'm just slightly too young to know the answer from actual enterprise experience. The only network cables I remember seeing personally in and around 1991 were 10Base2 (thin coax), AppleTalk (RS422/PhoneNet), and... well, okay, there was this crazy way to network Atari STs by hacking phone cords onto their MIDI ports... – Skyhawk Apr 2 '12 at 4:34
This is positively modern compared to some of the equipment our company specialise in. – Bryan Apr 2 '12 at 8:26
up vote 6 down vote accepted

Yes, it can be done.

Connect pin 3 (TxD-A) on each end to pin 5 (RxD-A) on the other. Connect pin 10 (TxD-B) on each end to pin 12 (RxD-B) on the other. On each end, connect pin 6 (Vc) to pin 9 (Collision Detect / Control In B). Connect the two ground shields together.

Note that while this usually works, it does technically violate the specifications, so it's an "at your own risk" kind of thing. Note also that this is not safe if both devices are not connected to the same grounding point.

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Pick up a used DELNI. DELNI And learn some new swear words for when you're latching and unlatching the &%$# !@!@! (*&^% sliders on the AUI cables.

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Positively brilliant! – Skyhawk Apr 2 '12 at 6:15
You don't actually want to do this, do you? If so, we either need Iain to chime in or I need to find a DELNI manual online to check if you need the little termination gizmo that plugs into port 9 (the female port with the [] on it). If you're using a DELNI standalone you have to slide the switch from [/] to [] and (I think) plug in a little terminator to that port. – Ward Apr 2 '12 at 6:19
You can slide the switch to the crossed position and connect an end node to the ninth port. I think. – David Schwartz Apr 2 '12 at 17:58

It may be easier/safer to use media converters that plug into the AUI on the device and provide an RJ45 connection on the other end.

enter image description here

They seem to be readily available still too.

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Of course that would be easier... in fact, being that I am under the age of forty, it is the only way I've ever seen an AUI port connected to a network. – Skyhawk Apr 2 '12 at 8:03
3Com also made some hubs with BNC and AUI ports, google for "3Com OfficeConnect Hub TP4Combo" – Ward Apr 2 '12 at 18:03

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