Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!caen!news.cs.indiana.edu!msi.umn.edu!noc.MR.NET!gacvx2.gac.edu!dan From: dan@gacvx2.gac.edu Newsgroups: comp.dcom.lans Subject: Re: 10Base-T hubs Message-ID: <1991Apr4.001006.177@gacvx2.gac.edu> Date: 4 Apr 91 00:10:06 -0600 References: <1991Apr03.004515.12021@rs6000.cmp.ilstu.edu> Distribution: usa Organization: Gustavus Adolphus College, St. Peter, Minnesota Lines: 107 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? I have found UTP to be more reliable than thin ethernet. We have been using thin ethernet in several building. I have found that the BNC connectors on thin ethernet do not take wear well. I have had faculty rearrange their office and take out an entire segment consisting of several offices, not because they are being malicious but just because they don't know better. In classrooms I use a $75 connector and cable from AMP that shorts out inside the wall when the cable is removed. Most faculty offices have a $8 wall plate with two BNC connectors on it. The real solutions are to use more expensive connectors, or change to a star topology (DEC recommends this in their local area networking books.) I have also found that the physics department likes to extend their cable on their own. When I finally caught up with them they had a network that was quite a bit over the 30 connections and 300 meters allowed in a thin ethernet. A unix computer on their segment could not be reliably accessed by users on other segments. The physics departments excuse was that I didn't make the rules clear enough and just how were they suppose to know the length of the cable. They still paid for the repeater and earned my ire. The faculty in the building I have using UTP ethernet have not been able to mess up the network yet. I have had some stations go bad in the lab due to strained cables, but a longer cable took care of that. > - 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? I don't know that active and passive hubs is a good way to describe the difference between the types of hubs. All hubs are essentially multi-port repeaters some have incorporated bridges or a high speed internal bus. The more expensive hubs usually include managment capabilities. This allows monitoring all the ports from one workstation anywhere on the ethernet. Most managment hubs allow the managment station to get the number of packets/bytes transfered through the port and also an error count. Many allow the management station to turn ports on and off. I have built a 60 computer network using the Asante hubs. They work well. They have no management capability. I did run into some problems with the Asante hub not being able to tell a shorted cable from a cable with a computer at the other end. I was told by another use of the hubs that this is because Asante used a single chip UTP ethernet controler that was designed for workstation and as uses the same link integrity pulse as a workstation, thus the loopback caused by the short could not be detected. I don't know if other hubs have the same problem, if they do then something more than a single LED is needed to signal an error. Having managment would help. I also had a problem with a 25 pair cable that was multipled to another punch block this cable caused the hub to go throught a cycle of powerup-error-reset-error-reset-... The whole hub did this making all the workstations on it unuseable. I have seen token ring hubs blow fuses in similar situation. More expensive hubs just cut out the malfunctioning ports. Fixing the cabling problem caused the hub to function normally. In a small network the Asante hub is adiquate. I do not plan to use it in the new Computer Science/Physics/Academic Computing building. There are more than 200 computers in this new building on three floors to start with, the building it being wired by the same contractor that is doing the phones and is going to be capable of supporting about 500 computers before we need to add wire. I am planning to use management hubs in this building. There is also significant need for traffic management in this building. > - 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? I use thin ethernet between the hubs. This reduces the repeater count and allows me to use the cascading feature in a room with one UTP port. I can plug in a hub and have 11. With RJ45 cords a quick network can be build in any classroom. We will be using this this summer as the summer programs here will out number our available computer labs since three labs will be closed while they are moving to the new building. I is also hand if the instructor wants to bring more than one computer into a classroom. Even in the new building I will probably have a couple of Asante hubs available for this use. > - (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? I compare 10BASE-T to a thin ethernet star. A thin eithernet bus does not have the same reliability characteristics as a star. It does have to be a strict star where the thin ethernet star can have multiple computers on each segment. I think you will find multi-port thin ethernet repeaters to as expensive as UTP hubs. I also use the UTP wiring for more than just ethernet, we also run token ring and rs-232 over it. It is also possible to run AS/400 twinax terminals and 3270 terminals over it using baluns. Arcnet is another possibility. I have found that a well built thin ethernet network and a UTP ethernet are about the same price per port. By well built I mean one with about the same reliability as the UTP network. I also strongly recommend purchasing a portable cable tester like the ones sold by MicroTest. They have been valuable in finding both thin ethernet and UTP cable problems. Also a cheap PC software package like Ether Monitor from Brightworks or NetCure/NetMon (available on the net) is very helpfull for locating problems. -- Dan Boehlke Internet: dan@gac.edu Campus Network Manager BITNET: dan@gacvax1.bitnet Gustavus Adolphus College St. Peter, MN 56082 USA Phone: (507)933-7596