bill@banana.fedex.com (bill daniels) (05/20/91)
James E. Gaskin, author of the "Networking" column in _UNIX Today_,
mentions in the 4/29/91 issue that we should
"Start working on your management by showing them how
little extra it costs to use fault-tolerant UTP rather
than fault-intolerant coax for new installations. Arrange
for a demo of a good management package, stressing
decreased downtime."
The column dealt with unshielded twisted pair, concentrators and
other UTP-oriented devices. Would someone please explain how UTP
and concentrators enable one to establish a more reliable net? This
was all news to me.
bill
--
these ravings are in no way sanctioned by federal express corp
bill daniels | voice: (901)797-6328
federal express corp | fax: (901)797-6388
box 727-2891, memphis, tn 38194 | email: bill@banana.fedex.comian@ukpoit.co.uk (Ian Spare) (05/21/91)
In article <1991May20.133442.1309@banana.fedex.com> bill@banana.fedex.com (bill daniels) writes: >other UTP-oriented devices. Would someone please explain how UTP >and concentrators enable one to establish a more reliable net? This >was all news to me. > With pleasure .... We have two nets for RD&D , one UTP and one Thin-ethernet. In the UTP net there is an ethernet repeater giving UTP ports , I can add or remove devices on this without knocking out the net ( unless the two devices are talking of course !!! ) compare and contrast with my thin net where speed is of the essence and all Unix consoles start getting retry counts exceeded etc. Also if a user has a PC , say 200 feet away , connected via UTP and has the cunning idea of re-arranging his furniture when he breaks the thinnet the whole segment doesn't go down. UTP wins hands down , but it's a pain when you run out repeater ports or just need an extra one for a demo and can't find one free. -- Ian Spare , iT , Barker Lane , CHESTERFIELD , DERBYS , S40 1DY , GREAT BRITAIN E-mail : ian@ukpoit.uucp - VOICE : +44 246 214296 - FAX : +44 246 214353
henry@zoo.toronto.edu (Henry Spencer) (05/22/91)
In article <1991May20.133442.1309@banana.fedex.com> bill@banana.fedex.com (bill daniels) writes: >... Would someone please explain how UTP >and concentrators enable one to establish a more reliable net? ... Assuming "UTP" means "10BaseT", the crucial issue is that 10BaseT is a star topology, with each host connected directly to the hub, whereas other forms of Ethernet are bus topologies, with more than one host hanging off of each piece of wire. Given good equipment design, star topologies have one big advantage: a foulup on one wire does not mess up anyone else. When Joe Random User disconnects his cable to move his machine from one side of his office to the other, only his own machine's connectivity is disrupted. If he's on a bus-topology network, he may well take down everyone who's on the same piece of cable. There is a dark side to this particular Force, of course. :-) If the central hub is down, *everybody* is out of communication. -- And the bean-counter replied, | Henry Spencer @ U of Toronto Zoology "beans are more important". | henry@zoo.toronto.edu utzoo!henry
smb@ulysses.att.com (Steven Bellovin) (05/22/91)
In article <1991May20.133442.1309@banana.fedex.com>, bill@banana.fedex.com (bill daniels) writes: > > The column dealt with unshielded twisted pair, concentrators and > other UTP-oriented devices. Would someone please explain how UTP > and concentrators enable one to establish a more reliable net? This > was all news to me. If a conventional or thinwire coax is opened or shorted -- to add a new transceiver, or because you want to reroute or extend the cable, or because some electricians decided it was in the way but that they could easily cut it and resplice it with black tape later, you lose your whole net. With UTP, everything is a ``home run''; a problem on one segment affects only that segment. Of course, a problem with the hub takes our your whole net, but that's often easier to find and fix than a cable problem.
barmar@think.com (Barry Margolin) (05/22/91)
In article <1991May21.172018.11672@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes: >Assuming "UTP" means "10BaseT", the crucial issue is that 10BaseT is a star >topology, with each host connected directly to the hub, whereas other forms >of Ethernet are bus topologies, with more than one host hanging off of each >piece of wire. Given good equipment design, star topologies have one big >advantage: a foulup on one wire does not mess up anyone else. We use an intermediate solution here. Our network is mostly thin Ethernet (we considered twisted pairs when we were rewiring, but I don't remember why we decided against it), with the large subnets implemented using a number of segments radiating from an intelligent repeater (Cabletron IRMs). Any one segment has about a dozen hosts on it, so a cable problem generally is limited to affecting that many hosts. The intelligent repeater isolates the segments electronically and can selectively shut down an individual port (either manually, or automatically upon certain triggers such as excessive error rates). -- Barry Margolin, Thinking Machines Corp. barmar@think.com {uunet,harvard}!think!barmar
jason@hpcndjdz.CND.HP.COM (Jason Zions) (05/22/91)
UTP is fault-tolerant in the sense that a cut cable generally affects only the single node attached to it; the UTP hub will detect that one of its ports is busted in some sense and take it out of the loop. If everyone was one a single stretch of coax, a cut cable would affect every node on that segment. Breaking the coax to insert another tee would stop the entire segment, while adding a new UTP line to a hub shouldn't affect any other users. Of course, you're still vulnerable on the 10Base2 or 10Base5 links between the hubs, and if you've cascaded hubs via UTP you have a larger vulnerability on the cascading UTP lines, but that's a lot more manageable than barrel and tee connectors etc. Also, you have the added vulnerability of an active device (the hub itself) which might fail and take out n devices with it. Jazz
jmd@EMPEROR.HANDHELD.COM (05/24/91)
Jazz writes: > ...but that's a lot more manageable than barrel and tee connectors etc. ... While not directly on the topic, AMP's thinnet tap system takes the pain out of 10base2 networks. The wall jacks make before break, allowing live disconnects, and there's only one cable and one BNC going to the CPU. They use a special twin coax cable fed to a special BNC that brings the center conductors together at the pin of the single BNC. So you can disconnect either the BNC from the CPU or the plug from the wall without interrupting the rest of the network. Jim De Arras
ken@dali.cc.gatech.edu (Ken Seefried iii) (05/24/91)
In article <886@Emperor.HandHeld.com> jmd@EMPEROR.HANDHELD.COM writes: >Jazz writes: > >While not directly on the topic, AMP's thinnet tap system takes the pain >out of 10base2 networks. One caveat here. While the AMP connectors are really neat most of the time, they are fragile. We tracked a nasty impedance problem down to an AMP wall connector that had been broken by someone backing a rolling chair into the plug. Other than that, I love 'em (I've got 60+ machines hooked up this way). -- ken seefried iii "I'll have what the gentleman ken@dali.cc.gatech.edu on the floor is having..."