10 Oct
2013
10 Oct
'13
8:03 p.m.
Paul, at Fuji we used the Dec bridge 500 and 600 series, the decconcentrator 550 and the
gigaswitch/fddi. It worked ver reliable to the point that I had serious problems obtaining
budget to put some redundancy in the LAN. Three rings needed at least 4 gigaswitches.
Hans
Van: Paul_Koning at Dell.com
Verzonden: donderdag 10 oktober 2013 16:26
Aan: hecnet at Update.UU.SE
Beantwoorden: hecnet at Update.UU.SE
Onderwerp: Re: [HECnet] FDDI advice
On Oct 10, 2013, at 8:44 AM, Brian Hechinger <wonko at 4amlunch.net> wrote:
On Thu, Oct 10, 2013 at 02:36:04PM +0200, Peter
Lothberg wrote:
Ah, time to dust off some dormant memories. I used to work on the FDDI standard at DEC;
this stuff is familiar.
"CDDI" is marketing slang; it is not standard terminology.
FDDI is different from Ethernet; the MAC layer protocol is completely unrelated. It's
quite similar to token bus (802.4), actually. (The only thing it has in commoni with 802.5
is the words "token" and "ring" -- apart from that, the two protocols
operate completely differently.)
FDDI connections have a "type", which can be "A", "B",
"S", or "M". "M" ports exist on concentrators. NICs will
have A and B ports, if there are two connectors on the NIC ("dual attached
station" or DAS) or an S port, if there is one connector (single attached station or
SAS).
You have a number of topology options.
If you have DAS NICs, you can wire any number of them together in a "dual ring".
That's the original FDDI topology, before DEC forced concentrators to be added into
the standard. To do that, connect the NICs in circular fashion, A to B. Connected that
way, loss of any single connection is handled transparently.
If you have SAS NICs. you can connect a pair of them (S to S).
If you have DAS NICs plus or or two SAS, wire the DAS NICs A-B in a chain (essentially a
dual ring cut open). Then connect a SAS to each end (or just to one end, if you have one
SAS). There is no redundancy in this config.
Finally, if you have any concentrators, you can build a tree config out of those. If so,
the M connectors connect to the NIC connectors (A, B, or S), and the concentrator's A
and B connectors either connect to M ports higher up in the hierarchy, or in a dual ring
if you have a ring of concentrators, or nowhere if you're at the root of a tree.
FDDI fiber connectors are standardized but different from fiber connectors used by other
networks. The connector is fairly large, flat rectangular with a shroud covering the fiber
ends. Connectors are keyed to match the port type, though you can omit the keys and just
wire carefully. Standard fiber is 62.5/125 micrometer, but 50/125 also works.
You can find more in the DEC Technical Journal, Vol. 3 No. 2, spring 1991. Or the relevant
ANSI/ISO standards if you are a masochist. The topology rules are described fairly well in
the concentrator article in DTJ, but their full glory can be found in the FDDI
"SMT" (station management" standard.
paul
FDDI/CDDI is a dual ring token ring bus, with 4470 MTU byte packets,
it has 802.-- frames. DEC had a mode where you turned the token off
and used it for ptp full duplex.
I didn't know about the ptp thing. That's nifty.
For example cisco/cabletron/crecendo had
ethnernet switches with a
FDDI uplink, that you could use.
DEC made one as well, it was that large modular thingie. I used to have
one. Never got it powered on as it was enormous.
But you need nothing to build a FDDI ring, its a
A and a B ring, you
can just plug the cards together with fiber-patch-cables.
Unless you have one of those obnoxious single attached station cards.
-brian