Path: utzoo!utgpu!utstat!jarvis.csri.toronto.edu!mailrus!ncar!ames!lll-winken!uunet!usna!tsmith From: tsmith@usna.MIL (Tim G. Smith ) Newsgroups: comp.dcom.lans Subject: Re: Thin ethernet questions Message-ID: <170@usna.MIL> Date: 27 Mar 89 20:39:54 GMT References: <724@m3.mfci.UUCP> Reply-To: tsmith@cad.usna.mil.UUCP (Tim G. Smith (Mechanical) ) Organization: U.S. Naval Academy, Annapolis Lines: 98 In article <724@m3.mfci.UUCP> bronson@mfci.UUCP (Tan Bronson) Asks about how to wire a new building for ethernet and writes: > 3) Having multiple(many) thin ethernet `backbones'. The involves > wiring groups of 5-8 offices with one `backbone' and then running > this backone back to the wiring closet. The nice part is we > can have up to 8 thin backbones leading into a single thin ethernet > repeater, and we only need one thin ethernet repeater per network. > The bad parts are: 1) if someone moves into an office which has the > `wrong' backbone in it we're going to have to create another > backbone, and 2) we're going to have to get a TDR to ensure this > all works! At my last job at the Naval Academy we spent a long time thinking about how to wire our buildings and eventually decided to use all thin ethernet and to use a star wiring configuration with each office wired back a the central wiring closet. Cabletron MR-9000 MPRs were used inside the wiring closet to to tie together all of the offices on one subnet. Thin coax runs were then used to run back to the central computer room where each subnet tied into the routers. If the distance from the wiring closet to the central computer room is over the limits (our typically weren't) point to point fiber systems can be used (Cabletron sells somes tuff that will do the trick- so does Codenoll). Once the data is in the computer room it can be tied together with bridges (blech! but if that is what turns you on go for it) or routers. All of the MPRs to do this were not cheap but in my opinion they were well worth the money. If you use MPRs you can save a lot of network debugging time- you just look for the faulted segment and then deal with it. The whole net does not come crashing done due to one fault. They are really great for making life easier on the network managers. They also keep one person from screwing up the net by pulling the network apart or taking of his terminator. If someone screws with the parts of the net accessible in his office he only takes himslf and maybe his officemate off the net. No one else gets affected. That is a real nice feature when you have a lot of naive users. Wiring each office individually also makes it easier when people move from one subnet to another (USNA subnets by departments and every summer offices get shuffled among departments). If all of the cables go back to the wiring closet you just switch the cable from one MPR to another when an office moves to a new subnet. (ie RM312 just became an Aerospace Eng office when it used to be a Mechanical Eng office- no problem move cable number 312 from the Aero MPR to them Mechanical MPR and everything is fixed). Another reason to use thinnet is that more and more machines are coming with on board XCVRs (and thus have bnc plugs on the back). All you do is run a piece of coax from the wall to the back of the workstation. If there is more than one machine in the office than you can daisy chain them together. If you have machines without internal XCVRs you just use a bnc connector to attach an XCVR to then thinnet and you are set. I much prefer thin coax over thick. USNA bought 1000' spools of rg58, strippers, connectors, and crimping tools and had no problem making all of our cable up. Our techs found that is was quicker and easier to "connectorize" rg58 then it was to to tap a thick coax segment. It is also easier to debug thinnet as you can unplug segments and terminate them any place you have an XCVR. As for having to buy a TDR, we have one which we use for both thick and thin coax. Can't run a network without one. All in all the intitial costs of wiring as above will be a bit higher than your option 3 but I think it will pay off in the long run. You will have lower maintenance costs and a lot more flexibility wiht this method. I would imagine that others will also suggest the same sort of wiring scheme. As an aside... Cabletron has also introduced a new box called a "Multi Media Access Controller" (or someting like that- I call them MMACs) which are chassis into which you mount various cards to tie your net together. There are thinnet cards, fiber cards, twisted pair cards, and maybe others (I am at home and don't have the info here- sorry). Everything is repeated to all the ports on all of the cards in the box. The MMAC also has a "brain card" which holds the master ports (2 AUI and one thinnet) as well as serial connector so you can talk to the brain. The brain comes in 2 flavors- smart and stupid- the smart brain is only a little more expensive than the stupid brain. The smart brain collects statistics and is supposed to allow the network manager to turn ports on and off and things like that. They come in 3 and 8 slot chassis. I seem to recall that a 3 slot chassis with 2 12 port thinnet repeater cards and the smart brain cost under 5k. I thought that was very cost effective since 3 MR-9000s would cost about 7200 and would also need 3 XCVRs and appropriate cables. The MMACs don't need XCVRs since they have thinnet ports on the brain card. As soon as they came out I ordered 3 of them- I never got to see them though as I left the Academy before they came in. hope this helps and good luck, Tim Smith (formerly of the US Naval Academy) US mail:US Army, BRL E-mail: SLCBR-SE internet:tsmith@brl.mil Aberdeen Proving Grounds, MD 21005-5066 uucp :...!uunet!brl!tsmith MaBell :(301)278-6678 (or 6808) Autovon: 298-6678