dixon@gumby.paradyne.com (0000-Tom Dixon(0000)) (10/09/89)
In article <27682@amdcad.AMD.COM> rpw3@amdcad.UUCP (Rob Warnock) writes: >You know, that actually brings up a good question. Repeaters SHOULDN'T >ground the cable on either side, but *a* ground for each thin Ethernet >must come from *somewhere*, and I doubt that most network installers >think to provide one. [It may be the case that these multi-thinwire >repeaters ground the "down leg" thinwires to their own chassis ground, >which would be the right thing to do in most cases assuming the chassis >ground is connected to the third or "green" wire, but they should never >ground the "up leg", i.e., the trunk or backbone connection.] But what about backbone thinnet segments? This means that a thinnet segment that runs from repeater to repeater would be a gound loop. This is not good. The Cabletron 8 port repeaters we use have 8 thinnet ports and 1 AUI port. I would assume that we should hook backbone thinnet to a non grounding transciever and hook that to the AUI port on the repeater. We presently are using the thinnet ports as you expect. Do any vendors make repeaters that have configurable ports that can either be grounded or not? Rob, Thanks for the brain food. I had not even thought of this before. >Rob Warnock >UUCP: {amdcad,sun}!redwood!rpw3 Tom Dixon AT&T Paradyne uunet!pdn!dixon
johng@trwind.UUCP (John Greene) (10/09/89)
In article <6638@pdn.paradyne.com> dixon@gumby.paradyne.com (0000-Tom Dixon) writes: >In article <27682@amdcad.AMD.COM> rpw3@amdcad.UUCP (Rob Warnock) writes: >>You know, that actually brings up a good question. Repeaters SHOULDN'T >>ground the cable on either side, but *a* ground for each thin Ethernet >>must come from *somewhere*, and I doubt that most network installers >>think to provide one. [It may be the case that these multi-thinwire >>repeaters ground the "down leg" thinwires to their own chassis ground, >>which would be the right thing to do in most cases assuming the chassis >>ground is connected to the third or "green" wire, but they should never >>ground the "up leg", i.e., the trunk or backbone connection.] > >But what about backbone thinnet segments? This means that a thinnet >segment that runs from repeater to repeater would be a gound loop. >This is not good. > >The Cabletron 8 port repeaters we use have 8 thinnet ports and 1 AUI >port. I would assume that we should hook backbone thinnet to a >non grounding transciever and hook that to the AUI port on the >repeater. We presently are using the thinnet ports as you expect. All of the Thin-Ethernet transceivers that I have seen (read "taken apart") have the shield AC coupled to the chassis ground. The "ground" being talked about recently has to do with providing a DC ground at a single point. Whether or not this is good practice I cannot tell you. It seems that if you provide a DC path to ground you are only asking to have your cable fried in the case of lightning. -- John E. Greene "People are just like frankfurters....You have to decide if you're going to be a hot dog or just another wiener" DLR TRW Information Networks Division 23800 Hawthorne Blvd, Torrance CA 90505 ARPA: johng@trwind.ind.TRW.COM USENET: ..trwrb!trwind!johng
cuacw@warwick.ac.uk (Malcolm Barker) (10/11/89)
In article <6638@pdn.paradyne.com> dixon@gumby.paradyne.com (0000-Tom Dixon) writes: > >But what about backbone thinnet segments? This means that a thinnet >segment that runs from repeater to repeater would be a gound loop. >This is not good. > Should thinnet segments even be run from repeater to repeater? I have a copy of IEEE Draft Standard 802.3 (November 1984) specifying 10BASE2 which in the SYSTEM CONSIDERATIONS section 10.7.1 states the following: 10base2 segments should not be joined to more than one 10base5 segment (i.e. 10base2 segments should exist at the periphery of the hybrid structure.). Malcolm Barker
newbery@rata.vuw.ac.nz (Michael Newbery) (10/12/89)
In article <6638@pdn.paradyne.com> dixon@gumby.paradyne.com (0000-Tom Dixon) writes: >Do any vendors make repeaters that have configurable ports that can >either be grounded or not? The 3Com modular boxes have a screw on each card that you shift to earth/not earth the segment. You can likewise elect to have internal 50Ohm termination or not. On the subject of earthing and noise---be very carefull about the quality of your transceiver cables. We traced a number of very high error rates to substandard xcvr cables. The cables worked OK in benign environments but were unsatisfactory in noisy ones (like machine rooms.) -- Michael Newbery<newbery@rata.vuw.ac.nz> (...!uunet!vuwcomp!newbery if you must) "MVS - well yes, it's big - but it IS slow!"
mhw@wittsend.lbp.harris.com (Michael H. Warfield (Mike)) (10/12/89)
In article <12@saturn.warwick.ac.uk> cuacw@warwick.ac.uk (Malcolm Barker) writes: >Should thinnet segments even be run from repeater to repeater? >I have a copy of IEEE Draft Standard 802.3 (November 1984) >specifying 10BASE2 which in the SYSTEM CONSIDERATIONS section 10.7.1 states >the following: > 10base2 segments should not be joined to more than one 10base5 > segment (i.e. 10base2 segments should exist at the periphery of > the hybrid structure.). Right. But all that is saying is that you don't run 10base2 to interconnect multiple 10base5 segments. You can certainly use 10base2 to interconnect multiple 10base2 segments. You only limits are the total number of repeaters you can have "in series". This is allowed: ( imagine repeaters drawn in at each junction :-) ) | | | | |_______________| | | 10base2 | |_______________| | | 10base2 | | | | | | | | | 10base2 | 10base2 | 10base2 | | | Why you would do this depends on your installation and the physical topology of the network you are laying out. -- Michael H. Warfield (The Mad Wizard) | gatech.edu!galbp!wittsend!mhw (404) 270-2123 / 270-2098 | mhw@wittsend.LBP.HARRIS.COM An optimist believes we live in the best of all possible worlds. A pessimist is sure of it!
haas%basset.utah.edu@cs.utah.edu (Walt Haas) (10/13/89)
In article <12@saturn.warwick.ac.uk> cuacw@warwick.ac.uk (Malcolm Barker) writes: >I have a copy of IEEE Draft Standard 802.3 (November 1984) >specifying 10BASE2 which in the SYSTEM CONSIDERATIONS section 10.7.1 states >the following: > > 10base2 segments should not be joined to more than one 10base5 > segment (i.e. 10base2 segments should exist at the periphery of > the hybrid structure.). Huh! Why not? -- Walt