Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!ames!haven!decuac!e2big.mko.dec.com!bacchus.pa.dec.com!decwrl!sdd.hp.com!zaphod.mps.ohio-state.edu!mips!prls!pyramid!voder!apple!sun-barr!cs.utexas.edu!usc!snorkelwacker!bu.edu!bu-it!kwe From: kwe@bu-it.bu.edu (Kent England) Newsgroups: comp.dcom.lans Subject: Re: 10Base-T and RJ-11 wiring? Keywords: 10Base-T, RJ-11 Message-ID: <62372@bu.edu.bu.ede> Date: 10 Aug 90 18:05:06 GMT References: <1990Aug9.185455.3488@portia.Stanford.EDU> Sender: news@bu.edu.bu.ede Reply-To: kwe@bu-it.bu.edu (Kent England) Distribution: na Organization: Boston University Lines: 79 In article <1990Aug9.185455.3488@portia.Stanford.EDU>, morgan@jessica.stanford.edu (RL "Bob" Morgan) writes: > > In particular, we'd like to buy off-the-shelf twisted-pair jumper > cables to connect between the RJ-45 connector on the computer's > 10Base-T adaptor and the RJ-11 on the wall. Are these available from > some place? Do they have a standard for how they make them up, or do > people just custom-order? > Ah, an opportunity to answer a question, rather than ask our RL "Bob" Morgan, the man who has been so helpful to everyone else on the net for years. Let me give some background for the benefit of others. RJ-11 is set-up pairwise like so: 3 2 1 1 2 3 and RJ-45 is set-up pairwise like so: 3 3 2 1 1 2 4 4 We usually number the RJ-45 pins like so; 1 2 3 4 5 6 7 8 and 10BaseT goes like; tx+ tx- rx+ ... ... rx- ... ... Pair numbers are determined by the punchdown sequence on the closet block and not by the jack pin numbers or wire colors. You see right away what the problem is. Only pair 1 and 2 match, but 10BaseT uses pairs 2 and 3 which don't match on the jacks. -------------------------------------------------------------- I would recommend replacing the RJ-11 and using standard patch cords. Asceming you have a single three pair cable to each outlet, you could pull out the single RJ-11 jack and install one or two jacks. You could simply swap the RJ-11 for an RJ-45. The RJ-45 would simply be missing the fourth pair. Terminate the pairs according to RJ-45 sequence. Or you could install a pair of jacks in place of one. The first jack could be RJ-11 with pair 1 installed where pair 1 belongs on a RJ-11. Install tip and ring on this jack for the phone. That jack is a replacement for the one you pulled out. The second jack is an RJ-45. Install pair 2 and pair 3 where they belong on a RJ-45. There will be no pair 1 or pair 4. Or you could jumper pair 1 from the other jack to pair 1 and allow a tip and ring on jack 2 as well as 1. You could use this jack for Ethernet or other data, like LocalTalk or RS-232. Don't jumper tip and ring if you are going to make this a general data outlet. We use straight-thru patch cords from the xcvr to the wall. We use RJ-45 exclusively and four pair circuits. Chuck von Lichtenberg (chuckles@bu-it.bu.edu) is an engineer in my group who has worked with Cabletron on twisted pair Ethernet for years. Chuck convinced Cabletron to offer a 50 pin connector on their concentrators and to do the cross-over inside their system. You can therefore use standard patch cords, standard 25 pair cables, and standard punchdown and jacks with Cabletron and their 50 pin interface. Cabletron listens and designs systems for large installation bases like ours. I believe we have 3-400 10BaseT ports today. If you use Synoptics or other hardware that offer RJ-45 connectors you will have to do your own crossover. We would recommend doing it at the interface to the concentrator, keeping all other hardware standard. --Kent