ragge@nada.kth.se (Ragnar Sundblad) (05/14/89)
I have so far had several kilometers of RG58 C/U been installed at my department and surroundings. We have made TDR's (looking as beautiful as I can which), run network benchmarks (showing no problems at all), etc on these installations, and have had absolutely no problems. I have until now not even considered bying the more expensive ThinWire cable that some vendors provide. (I personally think it would be easier to get it shorted, since the inner foil normally would not be cut of where the threads would be, but at the end of the PE filling, almost where the centerleader pin to the BNC starts. A small lose thread somewhere in there would probably not be to fun, maybe creating intermittent hard-to-find problems.) Now people that usually know something of what they are talking about, although they are sellers (not of the cable), have told me that it is not recommendable to build long (100<l<185m) networks with RG58, I should use this ThinWire cable instead if I don't want to get problems when there are many nodes connected. What are your experience? Is there anything in this statement? (I mentioned this to a cable seller. He told me that "it had something to do with the timing" (RG58 = ~0.66c, ThinWire = ~0.80c). As long as I don't run at the timing margins, I don't give very much for that (perhapse I could get 0.000001 times better performance :-).) Ragnar Sundblad, Systems engineer ragge@nada.kth.se
root@helios.toronto.edu (Operator) (05/16/89)
In article <1026@draken.nada.kth.se> ragge@nada.kth.se (Ragnar Sundblad) writes: > >Now people that usually know something of what they are talking about, >although they are sellers (not of the cable), have told me that it is >not recommendable to build long (100<l<185m) networks with RG58, I >should use this ThinWire cable instead if I don't want to get problems >when there are many nodes connected. > >(I mentioned this to a cable seller. He told me that "it had something >to do with the timing" (RG58 = ~0.66c, ThinWire = ~0.80c). As long >as I don't run at the timing margins, I don't give very much for >that (perhapse I could get 0.000001 times better performance :-).) We use RG58U for all our thinwire Ethernet segments, and have had no trouble with it (actually, I was under the impression that RG58 was the cable that ThinWire, i.e. 10BASE2, was actually spec'd around). There are up to 20 connections on some of them, which is 2/3 of the maximum in the specs, and the length ranges from about 75m-185m. The error rate is about .01% (i.e. 1 in 10000), although it's hard to tell what proportion of those errors are due to various factors such as interfaces dropping packets, systems putting out garbage, etc. etc. Thus the real network error rate is probably lower than this. I might add that the error rate on our coax is about an order of magnitude higher, but there are a lot more systems and thus there is more potential for junk. With only 185m of cable, I can't see timing being a problem. The difference in propagation time at .66c vs .8c over a 185m cable round trip is roughly 400ns, which is unlikely to affect the Ethernet timing (~50us window). Most of our thinwire segments run around the outside of a floor, i.e. along office windowledges and through walls (mostly plaster). When the cable is initially installed we insert a barrel connector in each place where a system might potentially be connected (min. 1 per room even where not planned). This usually results in about 15 connections, so there are some extras in large offices where more than one person works. We also try to cover the perimeter of the floor well under the length limit, so that there is allowance for extra pieces that people may need to reach a system in their office when it is eventually installed. Because of the existing connectors, it is very quick work to connect a system later on. Of course, we don't have to worry a lot about the aesthetics of the cabling. Basically as long as it isn't underfoot or otherwise in the way, nobody cares what it looks like (you should see the backs of our microVAXes!! :-) ). -- Ruth Milner UUCP - {uunet,pyramid}!utai!helios.physics!sysruth Systems Manager BITNET - sysruth@utorphys U. of Toronto INTERNET - sysruth@helios.physics.utoronto.ca Physics/Astronomy/CITA Computing Consortium
bud@ut-emx.UUCP (C. E. "Bud" Spurgeon) (05/17/89)
In article <802@helios.toronto.edu> sysruth@helios.physics.utoronto.ca (Ruth Milner) writes: >In article <1026@draken.nada.kth.se> ragge@nada.kth.se (Ragnar Sundblad) writes: >> >>Now people that usually know something of what they are talking about, >>although they are sellers (not of the cable), have told me that it is >>not recommendable to build long (100<l<185m) networks with RG58, I >>should use this ThinWire cable instead if I don't want to get problems >>when there are many nodes connected. >> >>(I mentioned this to a cable seller. He told me that "it had something >>to do with the timing" (RG58 = ~0.66c, ThinWire = ~0.80c). As long >>as I don't run at the timing margins, I don't give very much for >>that (perhapse I could get 0.000001 times better performance :-).) > >We use RG58U for all our thinwire Ethernet segments, and have had no >trouble with it (actually, I was under the impression that RG58 was the >cable that ThinWire, i.e. 10BASE2, was actually spec'd around). There are The IEEE 10BASE2 spec for thin Ethernet notes that the coaxial cable specifications are met by two cable types, RG58A/U and RG58C/U. From Belden cable RG58A/U is P/N 8259. It has a cellular polyethelyne dialectric, a nominal impedance of 50 ohms, a stranded center conductor, and a propagation rate of 78% of light. Belden sells RG58C/U as P/N 8262. It has a solid polyethelyne dialectric, 50 ohms, stranded, and a prop rate of 66% of light. Both cables can be strung to 185 meters and meet the Ethernet timing specs. The foam poly has better propagation, but beware of environmental hazards. In one building that had a lot of thin Ethernet we noticed that the tray into the wiring closet had a sharp edge on the end of it. The bundle of RG58A/U cables had enough weight that the cables were crimped going over this edge. Foam poly is easily deformed. The solid poly holds up better to the sorts of hazards these cables see. I seem to recall that DEC sells a special thinwire variation that has a smaller OD than either of these two cables and requires special BNCs and crimping tools. Make sure that whetever you buy fits the connectors and tooling you get. Most of the installation problems with this technology will be with connectors that aren't installed correctly. Plain old RG58/U (Belden 8240) has an impedance of 53.5 ohms and does NOT meet the 10BASE2 specs.
root@helios.toronto.edu (Operator) (05/18/89)
In article <13099@ut-emx.UUCP> bud@emx.UUCP (C. E. "Bud" Spurgeon) writes: >In article <802@helios.toronto.edu> sysruth@helios.physics.utoronto.ca (Ruth Milner) writes: >>We use RG58U for all our thinwire Ethernet segments, and have had no >The IEEE 10BASE2 spec for thin Ethernet notes that the coaxial cable >specifications are met by two cable types, RG58A/U and RG58C/U. [...] >Plain old RG58/U (Belden 8240) has an impedance of 53.5 ohms and does >NOT meet the 10BASE2 specs. It's the RG58C/U we use; apologies for any ambiguity there. I wasn't aware there was an RG58U as well. -- Ruth Milner UUCP - {uunet,pyramid}!utai!helios.physics!sysruth Systems Manager BITNET - sysruth@utorphys U. of Toronto INTERNET - sysruth@helios.physics.utoronto.ca Physics/Astronomy/CITA Computing Consortium
hatch@wasatch.utah.edu (Corey Hatch) (05/26/89)
In article <13099@ut-emx.UUCP>, bud@ut-emx.UUCP (C. E. "Bud" Spurgeon) writes: > > From Belden cable RG58A/U is P/N 8259. It has a cellular polyethelyne > dialectric, a nominal impedance of 50 ohms, a stranded center > conductor, and a propagation rate of 78% of light. You mean Belden 8219, not 8259. Your above parameters are correct for the 8219. Belden 8259 has a velocity prop of 66%c and has a solid polyethylene dielectric (but is also classified as RG-58A/U). Belden 8219 is the better cable. ///////////////////////////////////////\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ Corey Scott Hatch Kirk: "And that's when you hit hatch@cs.utah.edu the Klingons?!" Computer Science Department University of Utah *** LA LAKERS: Back to Back to Back *** \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\///////////////////////////////////////
bud@ut-emx.UUCP (C. E. "Bud" Spurgeon) (05/27/89)
In article <1927@wasatch.utah.edu> hatch@wasatch.utah.edu (Corey Hatch) writes: >You mean Belden 8219, not 8259. Your above parameters are correct for the >8219. Belden 8259 has a velocity prop of 66%c and has a solid polyethylene >dielectric (but is also classified as RG-58A/U). > >Belden 8219 is the better cable. > You're quite right! I goofed and gave out the wrong Belden number for the RG58A/U I was describing. While we're at it, I have a photocopy of the wire spec used by DEC in their DECconnect thin Ethernet system. It appears to have a Belden # of 9908. The main thing that I recall about using this stuff is that the outside diameter is smaller than the usual run of RG58A/U and the usual BNC crimp-on connectors won't crimp onto it properly. I was told that DEC uses this cable because it has a 100% foil shield along with the braid for better EMI characteristics.