Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!shadooby!samsung!caesar.cs.montana.edu!blake!djo7613 From: djo7613@blake.acs.washington.edu (Dick O'Connor) Newsgroups: comp.dcom.lans Subject: Ethernet over twisted pair: a summary of the "whys" Keywords: Ethernet, twisted pair, LANs, wiring costs Message-ID: <4686@blake.acs.washington.edu> Date: 29 Nov 89 22:43:41 GMT Organization: Univ of Washington, Seattle Lines: 133 Thanks to all of you who responded, both here and via email, to my questions about using Ethernet over twisted pair. The consensus seems to be that it is the wiring medium of choice where wiring installation will be the biggest expense. Other solutions probably are more optimal for small, isolated workgroups like the 7-station group I used as an example. Here are the comments I've received via email to date, excerpted (in *some* cases, at least :) with permission... ******************************************************** >From: wsmith@umn-cs.CS.UMN.EDU (Warren Smith [Randy]) Here are what I see as the advantages of twisted pair Ethernet: 1) Low cost for cable minimal benefit - labor is usually the major expense in a large installation, equipment is in a smaller one 2) Ability to use existing cable plant in some cases 3) Common wiring type (most of your installer types feel comfortable with it) 4) Small cable - fits in conduit easier (not much different from thinnet tho) 5) Don't have to worry about termination 6) Same wiring can have multiple uses (eg. telephone, Appletalk, RS-232) some won't view this as a feature when people plug things in wrong... And numerous other quibbles about how easy/nice/reliable/stupid/junky/etc the connectors are. The IEEE 802.3T standard is not low cost! This will hopefully change as 802.3T devices are mass produced, and vendors start competing. I have some doubts that it will ever be a super cheap option (comments?). Other non-standard twisted pair products can be alot cheaper. I really don't think there is any significant advantage to using a twisted pair product for the small workgroup as you described (7 stations in close proximity). I wouldn't relate the benefit of twisted pair to the size of the LAN, but rather the wiring requirements. Randy ----- ******************************************************************* From: osterman@snmp.ocf.llnl.gov This is an exciting new boon to the vendors of Ethernet equipment. Just imagine, now anyone who has a phone has the capability to install the vendor's Ethernet equipment. The greatest cost of any wire is the installation cost. If you have to install twisted pair then the cost of installing RG58 is not an inmportant cost difference. More can be done with the twisted pair however. (RS232, Apple Localtalk, etc.) There was talk from some FDDI vendors about CDDI (Copper Distributed Data Interconnect) using RG58, but I haven't heard anything about it in quite a while. >Perhaps cabling is easier, too. But is it really cheaper than standard >thinnet cable for small groups? Cabling is harder because you have more wires to deal with. (I had forgotten what a pain twisted pair was until I had to try to figure out why a particular Ethernet installation wasn't working and found that I had all of these possible wire combinations to deal with. (This installation used 3 pairs out of 4 and they had to be intermixed to satisfy both DEC and AT&T. The installers did the most logical thing and wired it one for one.) It is not cheaper to use twisted pair if you have to install wire, unless you worry about pennies per foot. >...But then you add in the $2500 12-port concentrator >necessary (?) for Ethernet over twisted pair, and suddenly you have a >*much* more expensive proposition than a standard coaxial bus arrangement. That $2500 concentrator may be the best thing that you ever put on your network. If it includes management and control capabilities you'll love it as the network grows. >I guess what I'm after is the answer to: Is twisted pair Ethernet a >special-purpose solution for large LANs (where wiring costs might predom- >inate) or small spurs off a large LAN? Where's the benefit for a small >standalone workgroup? All LANs start as small workgroup LANs. The trouble is that if you design them as small workgroup LANs you often have to redesign them later. If you design them as part of a large network at the beginning then they work just fine in the future and if the network never gets any larger, well, it's only money. (How much does it cost if your network goes down and the people who use are unproductive until it comes back up? $50 to $100 per hour per person?) One last thing. If thin wire has multiple taps on it then you better be able to see it all from one place or you'll regret it. ********************************************************** From: "Steven M. Miller" For small groups that don't move much it's no big deal. But, for medium and large size groups or small grups that move around a lot it's ideal. To hook my Sun up in a different office I'll just have to go to a patch panel and make 1 wire move and my Sun is hooked up if I'm using twisted pair. The initial costs are higher to install, but the costs of moving people around and adding new workstations are significantly lower. Plus I don't get the ugliess of thick or thin net cables. -Steve ************************************************************* From: Ken Yap I don't know the exact economics of this but my friend who works for a NYC brokerage firm was saying that twisted pair is a candidate where the wiring is already in place or the conduit space is limited, e.g. old buildings, and pulling thick ethernet cable through is a big hassle. I believe there is a shorter distance limit on thin ethernet, no? It looks like for new installations there is no advantage over thin ethernet as in your case. ************************************************************** From: bob@aecom.yu.edu (Bob Lummis) I doubt if anyone would claim ethernet over twisted pair would be better/ cheaper for connecting a small work group. The reason people get excited about it is that if your task is to provide a network for a whole campus it allows you to use twisted pairs that are already in the walls rather than pulling new cable. In a campus-wide network installation project the labor costs of installing cable are the most expensive item in the whole project. --- Robert C. Lummis, Director of Scientific Computing Albert Einstein College of Medicine, Bronx, N.Y. 10461 bob@aecom.yu.edu ...!uunet!aecom!bob *************************************************************** "Moby" Dick O'Connor ** DISCLAIMER: It would Washington Department of Fisheries ** surprise me if the Olympia, Washington 98504 ** rest of the Department Internet Mail: djo7613@blake.u.washington.edu ** agreed with any of this!