jwabik@uc.msc.umn.edu (Jeff Wabik) (02/19/91)
We're in the process of redesigning our internal networks, and plan re-think and re-implement how we do Ethernet and FDDI. In our most recent version of the design, we want to do the following to our FDDI network: Assume we have 4 machines (AA,BB,CC, and DD), each in a corner of a machine room. Normally, we might want to wire [sic] the room like this: ( = is the fiber ring ) +-------------------------------+ | AA=========================BB | | = = | | = = | | = = | | = = | | = = | | = = | | = = | | = = | | CC=========================DD | +-------------------------------+ For any number of reasons (which I'll share, if you care and ask), we do not want to lay fiber in this manner, but would rather buy some sort of "concentrator" box to "star" our ring. The box itself would have "n" fiber ports, would operate equivalently to a normal patch panel.. When a fiber pair is connected to a port, that pair becomes part of the ring.. When disconnected, the ring is still kept intact internaly. If I remember my ancient history, IBM has sold boxes like this for their token ring network for years.. It seems reasonable that such a box should exist for FDDI, although I have no idea if the switching should be optical or electrical.. (i.e. I'm a software guy.) If such a box exists, I'd appreciating learning about it.. Thanks! -Jeff -- Jeff Wabik E/Mail: jwabik@msc.edu Minnesota Supercomputer Center AT&T: +1 612 626 0211 Minneapolis, MN FAX: +1 612 624 6550
vjs@rhyolite.wpd.sgi.com (Vernon Schryver) (02/19/91)
There are FDDI "concentrators" which connect one or more stations to the
dual ring. Most FDDI concentrators should be thought of as complete
FDDI stations which also have electrical switches that connect additional,
"slave" optical cables in series with the concentrator's own hardware on
the dual ring.
Whether you use concentrators or not, it is good to connect FDDI machines
in a star, with all fibers connected to a patch panel. A patch panel
allows easy, manual reconfiguration, and costs little more when expensive
FDDI electronics are considered. All of the big fiber vendors make MIC
(FDDI) patch panels.
Ignoring patch panels and nonstandard topologies, there are 3 main ways to
connect FDDI stations:
1. single or dual attach stations with concentrators.
2. dual attach with optical bypass switches.
3. dual attach without switches.
Method 1 is most robust, but most expensive with lower potential performance.
Concentrators require more optical equipement and electronics per station
than other solutions. Optical bypass switches and the ODL (electrical-
to-optical hardware) are currently the most expensive FDDI parts.
A concentrator typically costs 0.25 more ODL's/station but saves 1.0 to
0.75 optical bypasses/station. (If you need robustness, you need
bypasses on the A/B ports of your concentrators. 4-port concentrators
seem to be popular.)
Using concentrators limits you <100Mbit/sec. There is hope of using
dual-MAC-dual-attach FDDI stations to get >100Mb. (The birthday
paradox ensures the 2nd ring is almost always available for data.)
Method 2 is almost as robust as 1, except that only a limited number of
consecutive stations can be "bypassed" with switches. (When the power
goes off or the station is reset, the switch passively drops into the
"bypassed" state.) With short cable runs and newer switches, this is
often not a problem. Switches are not cheap; they're mechanical devices.
Method 3 is fine in a computer room where the operators can run over
to the patch panel when the mainframe field engineers want to take down a
system. It is problematic elsewhere.
Most people and all FDDI concentrator vendors and central computer facility
managers say that concentrators are the only way to go. They note
concentrators allow multiple stations to be powered off without breaking
the ring. (Since FDDI is a dual-ring, any single station can be powered
off without breaking the ring, regardless of concentrators or bypasses.)
A surprising number of people do not know what a concentrator does. They
claim an FDDI concentrator can somehow isolate the ring from a misbehaving
station. This is false. All FDDI frames pass through all active FDDI
stations. The ring is not in any way protected from bogus frames by
concentrators. A concentrator can isolate stations that cannot do "CMT
signalling," but famous trade shows have demonstrated that is not a
problem. The infamous trade show problems have been frame problems, and
were not affected by concentrators, or, in one case I know of, were caused
by bugs in the concentrators themselves.
Vernon Schryver, vjs@sgi.comjbreeden@netcom.COM (John Breeden) (02/19/91)
In article <3517@uc.msc.umn.edu> you write: > > For any number of reasons (which I'll share, if you care and ask), > we do not want to lay fiber in this manner, but would rather buy > some sort of "concentrator" box to "star" our ring. The box itself > would have "n" fiber ports, would operate equivalently to a normal > patch panel.. When a fiber pair is connected to a port, that pair > becomes part of the ring.. When disconnected, the ring is still > kept intact internaly. > >If such a box exists, I'd appreciating learning about it.. > You just discribed AT&T's FDDI Concentrator. It does exactly what you discribe above. It's a 19" rack mountable card cage, able to hold 4 cards with 4 FDDI ports per card. Contact AT&T Computer Systems for more detail. -- John Robert Breeden, jbreeden@netcom.com, apple!netcom!jbreeden, ATTMAIL:!jbreeden ------------------------------------------------------------------- "The nice thing about standards is that you have so many to choose from. If you don't like any of them, you just wait for next year's model."
vjs@rhyolite.wpd.sgi.com (Vernon Schryver) (02/20/91)
In article <24647@netcom.COM>, jbreeden@netcom.COM (John Breeden) writes: > >You just discribed AT&T's FDDI Concentrator. It does exactly what you discribe > above. It's a 19" rack mountable card cage, able to hold 4 cards with 4 FDDI > ports per card. As far as I can tell, there are far more currently available brands of FDDI concentrators than FDDI stations. It's crazy, since no one can do anything useful with a concentrator by itself. The boxes all look similar. Some have more or less room for expansion. Some are slightly more or less expensive. None are cheap today--they're talking about thousands of dollars/port. I don't think concentrators make sense for most uses; most people disagree with me. The vast majority of the current FDDI Concentrator makers will be doing something else soon. Their market does not have room for much added value, and so will soon, if not already, be a "commodity market" with terrible margins. Those with deep pockets will be able to stay as long as they choose. The number of FDDI board makers is even stranger than the number of concentrator vendors. Everyone and their uncle has decided to start making (generally) very similar products, using nearly identical components, with very high non-recurring engineering costs, and with astronomical manufacturing and test costs. Lemmings are wierd. Vernon Schryver, vjs@sgi.com
sblair@upurbmw.dell.com (Steve Blair) (02/20/91)
SynOptics Communications also I believe has such a box. Their number is 800-776-8023, and ask for telemarketing.... not an employee of SynOptics, but used to be......now just a happy customer..... -- Steve Blair DELL UNIX DIVISION sblair@upurbmw.dell.com ================================================================
koning@koning.enet.dec.com (Paul Koning) (03/05/91)
|>... |> For any number of reasons (which I'll share, if you care and ask), |> we do not want to lay fiber in this manner, but would rather buy |> some sort of "concentrator" box to "star" our ring. The box itself |> would have "n" fiber ports, would operate equivalently to a normal |> patch panel.. When a fiber pair is connected to a port, that pair |> becomes part of the ring.. When disconnected, the ring is still |> kept intact internaly. |> |> If I remember my ancient history, IBM has sold boxes like this for |> their token ring network for years.. It seems reasonable that such |> a box should exist for FDDI, although I have no idea if the switching |> should be optical or electrical.. (i.e. I'm a software guy.) |> |> |>If such a box exists, I'd appreciating learning about it.. |> |>Thanks! |> |> |> -Jeff It sure does. It's called a "concentrator" (surprise!). You can get it from several vendors. I'll plug ours: the DECconcentrator-500, available in a variety of configurations (port counts, port types, media types). paul