Date: Sun, 12 Aug 2001 23:10:47 -0700 From: "Ted Mittelstaedt" <tedm@toybox.placo.com> To: "Doug Reynolds" <mav@wastegate.net>, <freebsd-questions@FreeBSD.ORG>, "James McNaughton" <jtm63@enteract.com> Subject: RE: Network throughput Message-ID: <003301c123be$b1e7c740$1401a8c0@tedm.placo.com> In-Reply-To: <20010813033331.290B637B408@hub.freebsd.org>
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>-----Original Message----- >From: owner-freebsd-questions@FreeBSD.ORG >[mailto:owner-freebsd-questions@FreeBSD.ORG]On Behalf Of Doug Reynolds > >as long as your not getting any outside rfi/electrical interference, >speaker or barbed wire work. trust me i've seen it done ! (i am I&M >tech). in most case, wire runs work great under CAT3, but if you are >going under 50-100ft with more than one number, go with CAT5 b/c of >less near/far-end crosstalk > Hi Doug, I hate to disagree with you here but DSL service is delivered over POTS lines that are generally buried in a 50 or 100 (or often much higher) cable binder that is in no way shape or form anywhere NEAR CAT-5, or even CAT-3 for that matter. The 50-100 feet of wire he has control over is going to be less than 1% of the total cable run of the average DSL installation (about 7K feet) It makes absolutely no difference what CAT-level the cable is going to be as long as there is some light twisting in the pairs. Remember this isn't Ethernet that we are talking about. As far as interference goes, generally the average DSL cable PUTS OUT a lot more interference than anything else your going to run into. In fact this is one reason that Qwest has dropped CAP encoding (such as used in the Cisco 675) and gone totally to DMT encoding (such as used in the Cisco 678) because they were finding in cable binders that contained many CAP DSL circuits that in some cases the circuits were actually interfering with other types of service in the same cable binder. This isn't publicized very much but it's buried in the Qwest documentation. For ADSL there are 6 critically important things that MUST be followed: 1) Distance of the entire run must be under 18000 feet. (actually, you can train at greater distances than this, but the training speed will be so low that you may as well use a modem) This of course is the length of the cable run, not the "as the crow flies" distance. 2) The entire run MUST use the same guage of wire. A guage change creates an impediance mismatch at some of the higher DSL frequencies that will harm throughput. This is often seen at ancient drop leads that come in from the outside Telephone Pole to the house - back in the old days the phone company sometimes used big, thick, copper-plated steel wire for these. Today, modern drop leads are all the same guage and they run fiberglass cables along with the pure copper pairs for strength. 3) There must NOT be any unterminated sections of the cable (ie: Bridge Taps) teed off of the main cable. Note that a homeowner can create bridge taps in their home that will be just as bad as the ones the Telco creates. 4) There must not be any load coils or other inductive loads in the circuit. (such as an extra 30 feet of cable wound up into a loop somewhere, or a ferrite bead on the cable somewhere, or passing through a "surge protector" or some such) 5) There must be zero or as close to zero ohms connection resistance at all punchdowns or other cable connections. (screw terminals, etc) 6) There must be no connections from either side of the pair to ground, or to other pairs. One thing he needs to do immediately is call the Telco and get ahold of a DSLAM tech. Modern DSLAMS have testing circuitry and you can do shorted and open pair tests on the pair that will discover most of these problems. (assuming the DSLAM tech knows what they are doing) Ted Mittelstaedt tedm@toybox.placo.com Author of: The FreeBSD Corporate Networker's Guide Book website: http://www.freebsd-corp-net-guide.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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