[geeks] Seeking network direction.

[Michael Parson]

On Tue, 16 Sep 2008, Joshua Boyd wrote:

> I'm trying to understand somethings about how ethernet works.  I would
> be happy for either answers, or pointers to free resources containing
> the answers would be even better.

<snip>

> Also, what is the relationship between AUI, AAUI, MII, and the phy
> chip on a embedded design that seems to say it speaks MII?  Also, I
> seem to recall once setting up a box with a lot of 15 pin connectors
> on it.  I believe a AUI adapter went on one of these to connect this
> box to a Cat5 switch, while the other 15 pin connectors were connected
> via 15 pin cables directly to an Onyx, a Sun 4/330, and a few IPC/IPX
> machines.  What was that thing?  It was considered somewhat out dated
> when I was touching it in the 1996ish time range.  I think it was
> referred to as a thicknet hub.

I can't answer the first set of questions, but I can help you with your
terminology a bit.

The 15 pin cable you're referring to is an 'AUI' cable.  They tended
to be run between old 10 megabit NICs and a transciever of some sort
that would convert the signal to either 10Base5 (thicknet), 10Base2
(thinnet), or 10BaseT (twisted pair).

One of the bits of old computing I carry with me from job to job is a
thinknet ethernet tap transceiver.  It has a 15 pin AUI connector.  I
also have the AUI cable for it somewhere packed away, it's about 15'
long, not really worth taking with me to work. :)

AUI == Attachment Unit Interface
AAUI == Apple AAUI, When Apple first started putting Ethernet on their
         Macintosh systems, they had a funny little connector, which required a
         transceiver for whatever type network you were connecting to.
MII == Media Independant Interface.  The updated version of the AUI, but
        the transceivers on them tend to convert to either twisted pair
        or fiber optic for Fast Ethernet (100 Megabit/s) or GigE.
PHY == The physical layer, copper, fiber, etc.

Some ethernet chipsets have a transciever built into the chip, some,
like the old DEC Tulip, used an external transceiver chip.

overly simplified, it kinda looks like:

MAC<->AUI/MII<->transceiver<->physical layer


> Anyway, I've been flipping through wikipedia and google, but I don't
> feel I've found the answers to these questions.  It isn't essential
> that I find them, but I don't like knowing there are things out there
> related to what I work on that I know so little about.

Here's an old paper about ethernet workings (100BaseT was still 'in the
works' when the paper was written):

http://www.ussg.iu.edu/usail/external/ethernet/ethernet-guide.html

I'm also a fan of the Free Online Dictionary of Computing (FOLDOC):

http://foldoc.org/

-- 
Michael Parson
mparson at bl.org