Re: AFP protocol

In article <1i7y12y.ztt1uk17xnij8N%dempson@xxxxxxxxxxxxx>,
dempson@xxxxxxxxxxxxx (David Empson) wrote:

Rowland McDonnell <real-address-in-sig@xxxxxxxxxxxxxxx> wrote:

Tim Streater <tim.streater@xxxxxxxxxxxx> wrote:

real-address-in-sig@xxxxxxxxxxxxxxx (Rowland McDonnell) wrote:

[snip]

There was also some funny Apple Ethernet card(s) that you had to buy an
adaptor for so you could connect it to the wiring. I don't think I ever
met that in real life.

Are you thinking of the cards with the AAUI adapter?

I think that's the one.

The original
ethernet spec called for various voltages to be sent down from the
computer to the transceiver,

???

Er?

That is quite correct, if you are using an AUI connector.

so the AUI connector and the up to 50m of
fairly heavy duty cable were a bit of a pain to deal with.

I met, in the 1980s, plenty of workstations hooked up to Ethernet
directly. I didn't see any wiring that looked a pain to deal with.

The original Ethernet, now known as "Thick Ethernet" (10Base-5) is a fat
an inflexible yellow coax cable which uses a "vampire tap" where you
push a sharp pointed plug directly through the outer insulation and it
pierces the inner core. These taps have to be a minimum of 1 metre
apart, and the network itself is permanent. The transceiver is mounted
directly on the vampire tap. A cable runs from the transceiver to the
AUI socket on the computer (DA-15). I expect this is the heavy duty
cable that Tim is referencing.

Yes. And getting the vampire tap right was a pain. You had to ensure you
cleaned out all the bits of the braided shielding from the hole. It
needed a special tool, too, to make the hole in the yellow cable. Right
at the start of things you couldn't get them I had to go down to 3Com HQ
and buy one for $50.

I've never seen one of these networks - they may have been used in some
places while I was at university (late 1980s) but out of sight.

The next generation was "Thin Ethernet" (10Base-2), which uses more
reasonable sized black coax cables that use BNC sockets, but can't
travel as far as Thick Ethernet (200 m instead of 500 m) and the network
has to be interrupted to connect or remove a transceiver or T-junction.

And the T had to be on the computer, not connected via a few feet of
cable to "make things tidier". We had to break the fingers of a number
of physicists at SLAC to stop them fucking with the network.

These can also be connected to an AUI socket, but it was more common by
the time I was using them to have a BNC socket on the computer, with a
T-junction to hook directly into the coax.

The third generation was "Twisted Pair" (10Base-T) which requires a
point to point connection using Cat3 unshielded twisted pair cables, and
RJ-45 plugs. It could also be connected to an AUI via the appropriate
transceiver, but it more common by the early 1990s to have a built-in
RJ-45 socket (Apple didn't catch up until 1995). These require a hub (or
switch) unless your network consists of only two devices.

Apple made the excellent decision to simplify that so you could connect
to the Ethernet with a few metres of much lighter cable - and a smaller
connector on the interface card.

Could you point me at some pretty pictures that show this? The Apple
way always struck me as being more awkward and done purely to wringe
more money out of the long-suffering customer who was resigned to having
to buy a special Apple adaptor any time he wanted to connect his Mac to
the non-Mac world.

I have no argument about Tim's claim of a smaller connector, but wasn't
aware that it helped to make the cable lighter.

My impression is that Apple's AAUI was just a different connector which
had the same signals as AUI, but in a smaller profile, and it avoided
the risk of confusing the standard Apple video connector (DA-15) with
the Ethernet socket. I haven't looked into the full technical details.

It allowed them to drop the no-longer-needed voltage supplies. And the
DB-15 with the slider was *not* consumer friendly.
.

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