Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!pasteur!ucbvax!TROUT.NOSC.MIL!carrs From: carrs@TROUT.NOSC.MIL (Stephen M. Carr) Newsgroups: comp.protocols.tcp-ip Subject: TCP/IP Fiber Optic Ring Backbone Message-ID: <8803292224.AA13808@trout.nosc.mil> Date: 29 Mar 88 22:24:22 GMT Sender: usenet@ucbvax.BERKELEY.EDU Organization: The Internet Lines: 104 ------- Folks, 1. We are in the process of admiring the pros and cons of implementing a fiber optic ring backbone versus a straight vanilla 50 Ohm baseband coaxial cable backbone to support IEEE 802.3 CSMA/CD Ethernet and TCP/IP. This backbone would support other subnets, as well as support a gateway for all subnets into the DDN MILNET. 2. We had somebody propose installation of a fiber optic ring as the backbone. They were adamant that this is an IEEE 802.3 CSMA/CD Ethernet solution that supports TCP/IP on top of it. I was taken aback, for I never heard of IEEE 802.3 implemented in a "ring" topology. Seems senseless to implement IEEE 802.3 in a "ring" topology to begin with, since IEEE 802.5 Token Ring is specifically matched to a ring topology. 3. Nevertheless, I am assured that just such a TCP/IP IEEE 802.3 CSMA/CD Ethernet solution in a fiber optic ring environment is available from Fibercom Corporation. 4. Aside from the fact that at first blush it appears silly to me to even try to implement IEEE 802.3 in a ring topology, I have other misgivings. a. The cost per device connection would be significantly higher. b. A fiber optic ring backbone, even if feasible in an IEEE 802.3 environment, is not as generic as a 50 Ohm baseband coaxial environment. In a 50 Ohm baseband coaxial environment, I can procure interface devices from several vendors at least. I fear that a Fibercom Corporation implementation of IEEE 802.3 in a fiber ring environment would lock us into procurement of gateway/router and interface devices from only one firm, "Fibercom". I wouldn't like to see us being maneuvered into procurement of a "vendor proprietary" solution with little flexibility regarding choice of gateway/routers and vendor interface devices. c. Implementation of IEEE 802.3 in a ring topology seems to me would require something akin to the opposite of IEEE 802.4 Token Bus. In other words, implement me a bus protocol in a ring topology. Not that IEEE 802.4 doesn't make sense, but it appears that essentially the MAP folks have implemented a ring protocol in a bus environment. I am sure they have their reasons, the MAP community isn't stupid. But what about implementing IEEE 802.3 in a ring topology? Is this for real? I confess, I am ignorant. d. I would think that in a ring topology, be it fiber or coaxial cable, by definition requires an order of magnitude greater configuration management overhead, in the sense that you can't just pick a 2 meter mark on an Ethernet cable and screw in a tap. Adding or deleting nodes in a ring topology seems to me requires very involved physical and software configuration management processes. Whereas management of a baseband Ethernet appears relatively simple, requiring no extraordinary services or talent. Hmmm, maybe somebody is setting themselves up for a LAN configuration management follow on contract. e. Fault isolation. I had been warned a long time ago about the problems encountered in fault isolating and repairing a ring topology. A baseband coaxial cable plant seems so much more straightforward and maintainable. f. We are talking about building a fiber optic backbone for one large building approximately 2 football fields long, and one football field wide. It is a one story structure. Since we do not exceed the limits of 500 meter segment and 2.5 kilometer span restrictions of 50 Ohm baseband coaxial IEEE 802.3, I don't understand what advantage a fiber optic ring is going to buy us in terms of distance. Besides, most if not all of the subnets within this building are going to be other 50 Ohm baseband IEEE 802.3 gatewayed/routed/bridged into this backbone. g. To the best of my knowledge, the FDDI (Fiber Optic Distributed Device Interface) standard has yet to be promulgated, and is still a draft standard. If we wanted to maintain interoperbility and conform to standards, I would think we should be picking FDDI as a target for a fiber optic backbone. Right now, I am not even sure of the correct physical specifications for an FDDI cable. Is this cast in concrete? Personally, I would avoid entertaining fiber optic backbones until such time that the FDDI standard is promulgated. 5. We have precious little networking experience, but this fiber optic ring solution seems to have gained a lot of popularity. I fear that people, in their zeal to become state of the art, are throwing caution, reliability, interoperability, and the KISS principle to the wind. 6. Can anybody comment and shed light on this situation? Does anybody have first hand experience with such a TCP/IP Fibercom Corporation IEEE 802.3 Ethernet fiber optic ring? My apologies for any statements above which may appear patently stupid from a technical perspective. Your candid response citing pros/cons and errors in my logic would be greatly appreciated. Very Respectfully, Steve Carr LCDR, SC, USN Navy Management Systems Support Office (Code 42A) Naval Air Station Norfolk, Virginia 23511-6694 Commercial: (804) 445-2171, 445-1595 AUTOVON: 565-2171, 565-1595 MILNET: carrs@nosc.mil navmasso42a@nardacva.arpa -------