djc@csun.edu (Dave Crawford) (10/07/88)
We would like to connect ethernet devices in four separate buildings with a fiber-optic backbone. Since we are linking together DEVICES rather than CABLE SEGMENTS, we hoped that we could use relatively inexpensive fiber-optic transceivers rather than fiber repeaters or star-topology hubs. The backbone we envision would look something like this: --------- --------- --------- --------- | FIBER |________| FIBER |________| FIBER |________| FIBER | | XCVR | | XCVR | | XCVR | | XCVR | --------- --------- --------- --------- | | | | | | | | ----------- ----------- ----------- ----------- | CISCO | | NOVELL | | NOVELL | |CABLETRON| |ETHER-X25| | SERVER | | SERVER | |MULTIPORT| | GATEWAY | | | | | | XCVR | ----------- ----------- ----------- ----------- In other words, we would like to set this up just as we would if we were using standard thick ethernet cable and transceivers. The entire fiber run would be less than half a mile. The buildings are virtually in a straight line. Is this a feasible plan? We are novices in using fiber, so we would welcome any advice, warnings or product testimonials. For instance, several companies (Black Box, Cabletron) market fiber transceivers that can only be used to terminate lengths of fiber. Since we are planning a daisy-chain, not a star, this type of transceiver wouldn't do the job. We've spoken with a company called Versitron that sells a "bus-topology fiber transceiver" that seems to be what we are looking for, but we have no experience with this company or its products. The alternative would be to replace each of the middle transceivers with two fiber repeaters connected to either end of a coax segment, then tap off of the coax with a standard transceiver. The sales rep from Black Box advised against this and said that we needed at least one "star-topology hub" in the network (we're not sure why). Is there an advantage in using repeaters and/or a central hub? This is a far more expensive solution to the problem. Dave Crawford Technical Analyst Cal State University, Northridge djc@csun.edu
kwe@bu-cs.BU.EDU (kwe@bu-it.bu.edu (Kent W. England)) (10/08/88)
In article <1581@csun.edu> djc@csun.edu (Dave Crawford) writes: >We would like to connect ethernet devices in four separate >buildings with a fiber-optic backbone. Since we are linking >together DEVICES rather than CABLE SEGMENTS, we hoped that we >could use relatively inexpensive fiber-optic transceivers rather >than fiber repeaters or star-topology hubs. You certainly can use fiber optic transceivers at the devices and this is relatively cheap. > >In other words, we would like to set this up just as we would if >we were using standard thick ethernet cable and transceivers. >The entire fiber run would be less than half a mile. The >buildings are virtually in a straight line. > >Is this a feasible plan? We are novices in using fiber, so we >would welcome any advice, warnings or product testimonials. > You can't really economically set up a fiber optic ethernet bus, you should use a fiber optic multiport repeater in a star configured arrangement. If you are going to the trouble to install fiber at all, I recommend using at least 12 strand cable, if not 24 or 48 strand cable. Most of the cost is in the installation. You could run a multistrand cable in a daisychain between your buildings and then connectorize or splice the fibers together in a logical star (with the hub in any building) without losing too much signal in the splice/connector. Then use fiber optic transceivers on the end of each spoke and an 8 port fiber optic multiport repeater at the hub. Much easier to maintain and that's the way most vendors design their fiber optic Ethernet systems. splice splice connect HUB |---------|----------------|---------------|--+ |---------|----------------|------+ | |---------|---+ | FOT MPR | | FOT FOT FOT You will have spare fiber left over and the star configuration is easier to manage so long as the hub is at the easiest location (ie in your area or machine room). You can always break this configuration up and splice it together in a new way if you ever have to move the hub or use the fiber for something like FDDI. Kent England, Boston University
henry@utzoo.uucp (Henry Spencer) (10/09/88)
In article <1581@csun.edu> djc@csun.edu (Dave Crawford) writes: >... we hoped that we >could use relatively inexpensive fiber-optic transceivers rather >than fiber repeaters or star-topology hubs... Uh, say what? You are assuming that your coax experience carries over to fiber unchanged. Sorry: it doesn't. There is no such thing as an "inexpensive fiber-optic transceiver". With coax, it's fairly trivial to put a bidirectional tap into the side of the cable without any other adverse effects. With fiber, THIS IS NOT TRUE. (Unless somebody has come up with something new recently.) In fiber, that operation is impossibly difficult. >... Is there an advantage in using >repeaters and/or a central hub? This is a far more expensive >solution to the problem. Using repeaters would be expensive (and would make the repeaters crucial to continued functioning of your network). But I don't understand why you think a star hub is expensive. Pull *one* cable, with eight fibers in it, along your route. Put your hub somewhere along it. Use two of the fibers to connect each node to the hub. If you put your hub in the central segment, you can get by with four-fiber cable. The reason why you should use repeaters or a central hub is because that is the practical solution with current fiber technology. -- The meek can have the Earth; | Henry Spencer at U of Toronto Zoology the rest of us have other plans.|uunet!attcan!utzoo!henry henry@zoo.toronto.edu
ron@ron.rutgers.edu (Ron Natalie) (10/11/88)
We've been using the Fibercom Ethernet product. Essentially this is a token ring network that has attach boxes that look like Ethernet transceivers to the host. You can make the Ring look like a bus as you picture (or you can make a star out of it, a true ring, a hat, or a big tree, or ...). -Ron The amusing thing is that the older single ring units work just fine even when they aren't plugged in. Our Fibercom rep was stumped by that. -Ron