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Conference 7.286::fddi

Title:	FDDI - The Next Generation

Moderator:	NETCAD::STEFANI

Created:	Thu Apr 27 1989
Last Modified:	Thu Jun 05 1997
Last Successful Update:	Fri Jun 06 1997
Number of topics:	2259
Total number of notes:	8590

1715.0. "DEChubs and single mode fiber?" by VMSNET::M_HYDE (From the laboratory of Dr. Jekyll) Mon Jun 12 1995 14:36

Hello,
    
Pardon me for barging in here - but I'm trying to steer some business
Digital's way.  I've tried to do some research on my own and now I'd like to
ask you folks. The college I attended has been given a gift of a large
amount of single mode fiber cable.

It seems that when reading about the DECconcentrator 500 series and related
modules there is a clear distinction between single mode adapters and
multimode adapters. However, when I start looking at the hub based products
there seems to be no mention of single vs multi.

Is single mode fiber useable with the DEChub 90/900 products?

Is there such a thing as a single to multimode adapter? (This may be a
ridiculous question but I don't know for sure.)

For a small campus, less than 2 miles across, is there a real use for single
mode or would they be better off trying to sell/trade it for some multimode?

Thanks for your help, after which I'll disappear quietly back into the mist.

mark

T.R	Title	User	Personal Name	Date	Lines
1715.1	Everyone has an opinion.....	CGOOA::PITULEY	Ain't technology wonderful?	`Mon Jun 12 1995 16:20`	21
	In my opinion........ In my opinion, the college would be better off trying to trade it for multi-mode fiber. Single mode fiber is useful for longer runs than the college will require. It will also make it difficult to easily integrate FDDI, Ethernet and any other technologies they may see fit to use on their campus. Digital's ethernet products use mutli-mode fiber intrefaces and the majority of the FDDI products do as well. There are, of course, Mod PMD's (modular physical media dependent) for devices like the 900MX concentrator but they are more expensive than the multi-mode PMD's. The extra distance that comes with single mode would no be required on this college's campus. .......In my opinion...... Brian Pituley NPC, Calgary
1715.2		STRWRS::KOCH_P	It never hurts to ask...	`Tue Jun 13 1995 00:16`	5
	In my opinion, they should try for an 80/20 mix. The single mode fiber may be required for high speed ATM connections between buildings. It's not clear whether multi-mode will be able to handle that speed at that distance.
1715.3		NETCAD::MELARAGNI		`Tue Jun 13 1995 07:56`	14
	Re .1: i would have to disagree with your assertion that one could not easily integrate FDDI and ethernet onto the same LAN -- this is precisely why we sell our line of work group bridges. Plug a DB900 into the hub backplane and you have FDDI/ethernet bridging. Nothing could be simpler. Also the distances that you're talking about -- 2mi (3.3km) -- is beyond the range of MMF fddi. If you wanted to traverse the total distance you'd need SMF. The other alternative would be to place MMF concentrators every 2km. But that could be more expensive than the single SMF link. bill BTW, current proposals for ATM OC-12 (622 Mbit/s) support 200m - 300m of MMF cable.
1715.4		CGOOA::PITULEY	Ain't technology wonderful?	`Tue Jun 13 1995 10:21`	21
	A rebuttal of .3's critique of my first response.... >> Re .1: i would have to disagree with your assertion that one could not >> easily integrate FDDI and ethernet onto the same LAN......... I know that integrating FDDI and ethernet into the same LAN is easily done. I have designed several LANs with just this as the goal. What I was saying (and I apologize if it wasn't clear) is that SMF is not useful in as many situations as MMF. For example, there are very few SMF ethernet devices. I realize now (thank you .2) that I was guilty of narrow thinking in my first response. A definitive answer to the college's quandry around SMF vs. MMF really should wait until a complete needs assesment and LAN design have been done. Any move to procure cabling (whether fiber or copper) before a design has been done is premature and will probably prove to be costly. Brian Pituley NPC, Calgary
1715.5	don't forget the premise	VMSNET::M_HYDE	From the laboratory of Dr. Jekyll	`Tue Jun 13 1995 12:22`	19
	But remember that the school has already been given a lot of single mode fiber. The question can be rephrased as: Given that they already have a lot of single mode fiber with zero investment - is it worth trying to use it everywhere as a fiber backbone? Or do the limited selection and expense of SMF devices make it more practical to simply unload the 'free' SMF cable and try to sell it or trade it for MMF - especially when, in typical small college style, they have minimal funds to spend? They are already a DEC shop system-wise, (cut my teeth there on a PDP-8), and I'm trying to show them that it's worth looking at DEChubs etc. for building the campuswide network. They think this free gift of single mode fiber is their ticket to a fiber based network and I'm trying to inject some reality. Thanks for your comments so far. I'm still lurking. mark
1715.6	A simple (I hope) answer....	CGOOA::PITULEY	Ain't technology wonderful?	`Tue Jun 13 1995 16:16`	14
	IMO.... I do not believe that it is worth it to try to "force" any network to use exclusively SMF fiber. Given the state of technology, it is also unrealistic. I don't want to sound like a broken record but.....The final determination needs to be made after a network design has been done. It might turn out that some of the SMF can be used and the remainder traded or sold. Brian Pituley NPC, Calgary