Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!pacific.mps.ohio-state.edu!linac!att!news.cs.indiana.edu!msi.umn.edu!noc.MR.NET!jhereg!andrew From: andrew@jhereg.osa.com (Andrew C. Esh) Newsgroups: comp.dcom.lans Subject: Re: 10Base-T hubs Message-ID: <1991Apr3.161219.19343@jhereg.osa.com> Date: 3 Apr 91 16:12:19 GMT References: <1991Apr03.004515.12021@rs6000.cmp.ilstu.edu> Distribution: usa Organization: Open Systems Architects, Inc., Mpls, MN Lines: 72 In article <1991Apr03.004515.12021@rs6000.cmp.ilstu.edu> ejbehr@rs6000.cmp.ilstu.edu (Eric Behr) writes: >We're considering using our twisted pair wires for Ethernet. Hence tons of >questions, some of which are below: > >- aside from distance/no. of stations differences, is UTP inherenly less >reliable than thin/thick E-net? > UTP? Unshielded Twisted Pair, I assume. Since the inclusion of Link Pulse, I have found 10baseT to be much more reliable. One bad node doesn't affect any of the others, and the bad one is obvious. The wiring can be tested with a continuity tester, and it either works or it doesn't. Shielded wire is prone to problems that are marginal, and hard to locate without a Cable Scanner or a Time Domain Reflectometer. Connectors are much easier with 10baseT, and the distribution blocks and wiring schemes are ones that any telephone contractor can handle. >- in a smallish network (30 nodes, less that 300 ft.) is a passive hub OK? >Price difference between active and passive hubs is substantial... > >- has anyone had any experience with the passive 12-port hub from Asante? By the way, 384 feet (100 meters) is the limit for 10baseT, so 300 feet is not what I would call small. Passive and active hubs? I didn't know there was such a thing as a passive hub. Either way, the wiring is the same, so I would wire it, and then get a cheap hub on evaluation. If it runs, go for it. Be sure it is advertised as 10baseT. Ones I have tried out or helped beta test are David, Xyplex, ODS, and others. Please tell me about the active and passive deal though. This is interesting. I have no experience with Assante. > >- is there any advantage to "cascading" hubs (attaching the next one to a >port in the previous one - you lose two ports) as opposed to putting both >directly on a thin/thick backbone and using all ports for the UTP star? Lose two ports? If you are connecting two "out" ports together, you will have problems. To cascade, you need to connect an out port of the parent, to the AUI port of the child, with a 10BaseT transceiver. Without the tree heirarchy, the timing gets all crunched and one or both of the hubs will stop working until the problem is corrected. Also, I would not cascade more than two levels. Although I have not tried it, I have had experience with time delay problems with other types of hubs if there are many cascades. You need to figure a loss budget for the retransmission time, and see if it stays within the net specifications. > >- (must be obvious...) does 10Base-T *have* to use star topology? >If so, then (troubleshooting aspects set aside) I save maybe $500 in >thinwire cabling costs but I lose $1000+ on a hub... I think that >10Base-T's economic advantages are a bit overblown given the current >prices; am I right? > Yes, 10baseT has to be star, just like telephones. When you consider costs, compare the cost per foot of wire, connectors, wiring blocks, manpower for installation, and the rental or purchase of test equipment to certify that the net is correctly installed. A Pair Tester is a lot cheaper than a Cable Scanner, and a four year old can operate it. Maintenance should also be figured. I have found Thin net to be prone to connector trouble after a few months getting kicked around under the desk. UTP is less sensitive to this sort of thing. >Thanks very much for answers/opinions. E. >-- >Eric Behr, Illinois State University, Mathematics Department >Internet: ejbehr@rs6000.cmp.ilstu.edu Bitnet: ebehr@ilstu -- Andrew C. Esh andrew@osa.com Open Systems Architects, Inc. Minneapolis, MN 55416-1528 So much System, (612) 525-0000 so little CPU time...