Date: Mon, 13 Aug 2001 21:33:21 -0400 From: "Doug Reynolds" <mav@wastegate.net> To: "freebsd-questions@FreeBSD.ORG" <freebsd-questions@FreeBSD.ORG>, "Ted Mittelstaedt" <tedm@toybox.placo.com> Subject: RE: Network throughput Message-ID: <20010814013546.490FA37B40D@hub.freebsd.org>
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On Sun, 12 Aug 2001 23:10:47 -0700, Ted Mittelstaedt wrote: > 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. oh I agreed. I've popped open more than pick-terminal that didn't meet any standard at all, except for maybe the yarnball standard. the only reason i suggest CAT5 is because a lot of houses i goto have anywhere between 14 and 24 jacks that home run from the garage, and are at least 200 feet long. 20 x 200 is 4000ft of wire that are stapled in place. > 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. it doesn't surprise me, but i am a pots tech, and dont run into more than one dsl line every once in a while >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. that i do know, what kind of speed would you get at 18k ft? just curious, that is how far i am from the co. >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. I've seen 60k dls w/ 618k dsl, on old 18 gauge single pair. I don't know how much that is followed, or how it affects it. most cables are 24gauge in my area, and the drops are 22gauge. >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. hehe.. you'd be surprised, really. >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) yeah, most long cable runs here have a lot of load coils down here. they also have a lot of lightspanned boxs, and PG boxes over here, which according to the production techs i've talked to say that they still havent figured a way to switch dsl through them.. i find that hard to believe with fiber.. i could see it being a problem with copper though. >5) There must be zero or as close to zero ohms connection resistance at all >punchdowns or other cable connections. (screw terminals, etc) regular pots lines need that too, but not as bad. >6) There must be no connections from either side of the pair to ground, or to >other pairs. that goes for anything- have a tip to gnd or ring to gnd short, you'll have a little hum to no dialtone, depending how bad it is. >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) most splicer techs where i work carry good fluke meters to test for that. --- doug reynolds | the maverick | mav@wastegate.net To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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