(FDDI) Re: Old network interfaces still alive?

[Julian Coleman <jdc%coris.org.uk@localhost>]

Hi,

> IIRC FDDI is more like token ring than ethernet (wakkypodea suggersts it
> is token bus), I think that means you can connect machines directly to each
> other - although the cabling would get confusing!

Most devices that used FDDI were dual-attached, with an A and a B connection.
To create a ring, devices were daisy-chained ogether, with a connection from
the A port on the first device to the B port on the second, and so on until
the A port on the last device was connected to the B port on the first, thus
completing the ring.  The FDDI (MIC) connectors:

  http://www.fiberoptics4sale.com/Merchant2/fofs_img/clip_image023.png

had 3 keyed and coloured inserts (stored in the dust cover) so that they
could be connected up the correct way (cables would be usually be keyed as
A->B).

So, connecting devices is simple, as long as they are dual-attached.  Single-
attached devices were usually connected to a concentrator, as with only a
single connector, their "ring" could only have two devices.

> 100M ethernet is enough to kill FDDI - since it has fewer failure modes.

For backbones, the resilence of the dual-attched ring was quite nice - breaks
were atomatically handled by wrapping the ring.  For desktops, 100Mb ethernet
became a lot cheaper (and smaller) than FDDI, and CDDI didn't really take off,
even though it used the same twisted pair cabling as ethernet.

It's still possible to obtain SBus cards like the one shown on "wakkypodea".
However, I don't know of any with documentation to enable a driver to be
written, so the DEC cards are probably the only ones that we can support.

> ATM to the desktop was, of course, still born :-)

But, PPPoA is almost ubiquitous in the UK now, so ATM isn't quite dead ;-)

Thanks,

J

PS.  The HP docs have quite a nice overview of FDDI:
     http://docs.hp.com/en/J2157-90006/ch01s06.html

PPS.  I used to help run a university network, where the backbone (and a link
      to a neighbouring university) was an FDDI ring based on Cisco AGS+ and
      later 75xx routers.  The backbone ring was about 3km around and was very
      reliable (I can't remember that it ever failed).

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