[HECnet] FDDI advice

[Kari Uusim ki]

On 10.10.2013 18:27, Paul_Koning at Dell.com wrote:

On Oct 10, 2013, at 10:53 AM, Mark Wickens <mark at wickensonline.co.uk> wrote:

On 10/10/2013 15:29, Brian Hechinger wrote:
All this talk of FDDI makes me want to go get the 4000/500s. I have a
pair of QBus FDDI cards. I suppose I would have to make the Octane a
router between FDDI and ethernet. :)

-brian

On Thu, Oct 10, 2013 at 02:26:23PM +0000, Paul_Koning at Dell.com wrote:


If you have SAS NICs. you can connect a pair of them (S to S).


Thanks for all the info guys, I knew you'd be one hell of a knowledgeable lot!

If I understand what you are saying correctly, if I have NODE3 with the Turbochannel FDDI card (copper based) and a.n.other (call it NODE2 for arguments sake) ALPHA with a PCI FDDI Copper card I could wire them too together directly?

If that were so I would presumably need to do some routing within NODE2 to allow NODE3 access to network traffic if NODE2 was also connected to the 'great wide world' via ethernet.

Is there anything I'm missing in this picture?

You have the picture.   You'll need a crossover (not straight through) cable.   I went looking for data on the pinouts.   It turns out the pins used by FDDI TP-PMD ("Twisted pair physical medium dependent layer") are distinct from 100Base-T, but a crossover cable that has all four pairs wired should serve.   According to http://bitsavers.informatik.uni-stuttgart.de/pdf/national/_appNotes/AN-0965.pdf, pins 1/2 are the transmit pair, 7/8 the receive pair.

So a SAS connection is like a point to point Ethernet connection: exactly two stations.   Yes, that means that one (or both) endpoint needs to be either a bridge or a router for you to reach other nodes.

Earlier there was mention of the DEC full duplex mode.   You can turn that on for this topology, if you want to.   It may not be worth the trouble; the token ring overhead is pretty modest for short connections.

	paul

.


DEC used to have the BN26S-xx cable for FDDI twisted pair connections.
It has two pairs which are crossed and the pinout is 12----78


Kari