libove@lemans.det.dec.com (Jay Libove) (09/04/90)
From article <8499@accuvax.nwu.edu>, by dave%westmark@uunet.uu.net (Dave Levenson): > For two-line service, they should use a cable with two (or more) > twisted pairs. If they did, they would probably have connected one > line to the blue-white pair and the other to the orange-white pair. > If they did that, you shouldn't experience crosstalk, regardless of > the connectors used. Well, I have two phone lines - one voice, one data - on a four wire typical phone line, and I experience crosstalk that I believe might actually occasionally interfere with my data communications, and is always annoying (to both parties) on the voice line. Do I have any legal right to make the phone company come in and correct a situation that they caused? They knew before doing the second line "installation" (just plug in a two-jack plate and split the wires, $75, on top of $40 'line charge' !!!) that the line was to be used for data communication. Thanks, Jay Libove libove@kamet.enet.dec.com Digital Equipment Corp decwrl!"kamet::libove"
rac@uunet.uu.net (Roger Cornelius) (09/07/90)
From article <11734@accuvax.nwu.edu>, by libove@lemans.det.dec.com (Jay Libove): > Well, I have two phone lines - one voice, one data - on a four wire > typical phone line, and I experience crosstalk that I believe might > actually occasionally interfere with my data communications, and is > always annoying (to both parties) on the voice line. > Do I have any legal right to make the phone company come in and > correct a situation that they caused? They knew before doing the > second line "installation" (just plug in a two-jack plate and split > the wires, $75, on top of $40 'line charge' !!!) that the line was to > be used for data communication. When I had my second line installed, I specifically requested a completely separate line coming off the pole because I had heard of problems like the above. The phone company didn't seem to mind, and there was no additional charge either. Some months later, someone pointed out that once my two lines connect to the pole, they're connected back to a single line -- with everyone else's in the neighborhood to boot. Makes sense to me, but then I know next to nothing about phone systems. I've never had a problem with crosstalk on either line, but that may only be coincidence. Does having the separate line really make a difference? Roger A. Cornelius rac@sherpa.UUCP uunet!sherpa!rac
john@bovine.ati.com (John Higdon) (09/07/90)
Jay Libove libove@kamet.enet.dec.com writes: > [complaint about data/voice crosstalk] > Do I have any legal right to make the phone company come in and > correct a situation that they caused? They caused? If you are using standard red/green/yellow/black non-twisted pair IW then it is your problem. If they come in and fix it they have every right to charge YOU time and materials. Telco is not responsible for your interior wiring and they are not responsible for determining if your wiring is suitable for your intended use. I would be almost willing to guarantee that the crosstalk is not occurring outside of your premesis. Frankly, if you don't know what you are doing, then you should consider having someone come in and help you. It will be cheaper than having telco do it. John Higdon | P. O. Box 7648 | +1 408 723 1395 john@bovine.ati.com | San Jose, CA 95150 | M o o !
MERRIMAN@ccavax.camb.com (George Merriman -- CCA/NY) (09/07/90)
In article <11734@accuvax.nwu.edu>, libove@lemans.det.dec.com (Jay Libove) writes: > Well, I have two phone lines - one voice, one data - on a four wire > typical phone line, and I experience crosstalk that I believe might > actually occasionally interfere with my data communications. . . The standard TELCO four-wire cable known around here as "quad" (I've also known it as JKT) does NOT consist of two twisted pairs. I don't think the standard four-wire outside drop wire (black rubbery sheath with Copperweld conductors) does either.
Julian Macassey <julian@bongo.uucp> (09/07/90)
In article <11734@accuvax.nwu.edu>, libove@lemans.det.dec.com (Jay Libove) writes: > Well, I have two phone lines - one voice, one data - on a four wire > typical phone line, and I experience crosstalk that I believe might > actually occasionally interfere with my data communications, and is > always annoying (to both parties) on the voice line. > Do I have any legal right to make the phone company come in and > correct a situation that they caused? They knew before doing the > second line "installation" (just plug in a two-jack plate and split > the wires, $75, on top of $40 'line charge' !!!) that the line was to > be used for data communication. Legally, the Telco gave you what you asked for, a second line connected to a jack. For $50.00 you could have got a freelance to do it right. It's quad vs. twisted pair time again. Most domestic installations use cable that has a white plastic jacket. This cable has four wires inside. The four wires make up "two pairs". The first pair, the wires that carry the first line, are the Red and Green. Most telephone wire, like the wire going all the way back to the CO (exchange) is what is known as twisted pair. It is twisted so as to remain balanced to ground and null out induced signals. You can lay hundreds of twisted pairs next to each other with no crosstalk problems. None of the above refers to quad. Quad is not twisted. Using quad can give rise to cross talk. The longer the quad run, the greater the chance of cross talk. One "Okie fix" to quad cross talk is use a separate piece of quad cable for each line rather than use the Yellow and Black second pair. The best thing to do is rip out all quad and install "Three Pair". This stuff uses a different colour code: white/blue-blue/white, white/orange-orange/white, white/green-green/white. This job is easy to do. Three pair is cheap, you can get 1,000 Feet for about $40.00 (Your milage may vary). The jacket of twisted pair is usually "artificial limb pink" which is for some reason called "beige", it is available in "designer grey", I have seen some black jacketed twisted pair. The drop wire. This is the overhead cable that brings the line into some domestic installations. If it is a single line drop, the wire is not twisted. It is also flying through the air so is not liable to suffer from crosstalk. Multi-line drop wire, six pairs etc, is twisted pair. All the underground subscriber feeds I have seen use twisted pair. So it is very simple, want clean quiet lines? Use twisted pair. The Telco will usually use quad in domestic and single line installs. Installers are often happy to use twisted pair if you ask for them. But, you don't have to get the Telco to do your inside wiring, you can do it yourself or pay anyone else to do it. The Telco has priced themselves out of the inside wiring biz and their standards seemed to have slipped post divestiture. Julian Macassey, n6are julian@bongo.info.com ucla-an!denwa!bongo!julian N6ARE@K6IYK (Packet Radio) n6are.ampr.org [44.16.0.81] voice (213) 653-4495
tcora@pica.army.mil (Tom Coradeschi) (09/07/90)
With all the discussion of crosstalk between data and voice lines run
in the same physical cable, I thought I might relate our experiences
here.
Our building was recently (like one year ago) rewired for phones. Each
phone has an individual drop, with three pair feeding it. Aside from
upper level mucky-mucks, no phone uses more than one pair (the Army
doesn't allow us lowly engineers the "luxury" of a two-line phone).
At about the same time, we replaced the LocalTalk cabling we bought
from Apple with PhoneNet. PhoneNet uses twisted pair phone lines to
network Macs, IBMs, and the like at 230kbps using AppleTalk protocols.
Not ethernet speed, but faster than walking around the office with
diskette in hand. And AppleTalk is built into every Mac ever sold.
We set up a six node star, with each node being an office. We then ran
a backbone around the perimeter of each office, with RJ-11's about
every ten feet. To get into each office, we used one of the existing
three pair phone lines.
The phone on my desk and the PhoneNet drop into my office use two pair
from the same line. I've honestly never noticed ANY noise in the phone
line - and I spend a LOT of time on the phone - and never noticed any
AppleTalk problems due to the phone being in use. This goes for both
voice transmissions, as well as data, i.e. modem (remember, I don't get
two lines:-{).
So, I guess what I'm wondering is - what's the problem? Is it possible
that the problems others experience, or think they experience, are due
to other factors? Poorly terminated lines, bad grounds, etc?
tom coradeschi <+> tcora@pica.army.mil <+> tcora@dacth01.bitnetesmith@apple.com (Eric Smith) (09/10/90)
In article <11864@accuvax.nwu.edu> tcora@pica.army.mil (Tom Coradeschi) writes: > The phone on my desk and the PhoneNet drop into my office use two pair > from the same line. I've honestly never noticed ANY noise in the phone > line - and I spend a LOT of time on the phone - and never noticed any > AppleTalk problems due to the phone being in use. This goes for both > voice transmissions, as well as data, i.e. modem (remember, I don't get > two lines:-{). That's because LocalTalk (the physical layer, AppleTalk is the protocol stack) uses much higher (non-audible) frequencies. Voice or modem one the main pair and LocalTalk on the secondary pair may have some coupling, but will not interfere with each other under normal circumstances. I have a Telebit Trailblazer+ and my voice line on two pairs on one cable at home, and the coupling is very obvious to me, but people I talk to claim not to hear it. I plan to rewire using real twisted pair in the near future. Eric L. Smith Opinions expressed herein do not necessarily reflect those esmith@apple.com of my employer, friends, family, computer, or even me! :-)
kravitz@ucsd.edu (Jody Kravitz) (09/13/90)
My house is wired with three-pair twisted pair wire. Two are for voice, and the third is for a Trailblazer. I NEVER hear the Trailblazer in either of the voice lines. One of my phones is an old 2515BM (two-line WE, mechanical hold). I made a very long modular cord for it (over 30 feet). There is appearant crosstalk now between the two voice lines where there was none before. The modular cord is not twisted pair and appears to be a contributing factor. Jody Internet: foxtail!kravitz@ucsd.edu uucp: ucsd!foxtail!kravitz
carroll@beaver.cs.washington.edu (Jeff Carroll) (09/14/90)
In article <11864@accuvax.nwu.edu> tcora@pica.army.mil (Tom Coradeschi) writes: >The phone on my desk and the PhoneNet drop into my office use two pair >from the same line. I've honestly never noticed ANY noise in the phone >line - and I spend a LOT of time on the phone - and never noticed any >AppleTalk problems due to the phone being in use. >So, I guess what I'm wondering is - what's the problem? Is it possible >that the problems others experience, or think they experience, are due >to other factors? Poorly terminated lines, bad grounds, etc? As others have pointed out, the problem in the particular case of the guy who started the thread is that he probably wasn't using twisted pair in his premises wiring. Just running four wires can cause all kinds of undesirable electromagnetic coupling between wires that aren't supposed to couple. With all due respect to Mr. Higdon, however, it is quite possible for crosstalk problems to arise in telco cabling. Two of the most likely culprits that come to mind are (a) improperly insulated cable (e.g., rural areas where paper-insulated cable is still in service, and the insulation is getting wet. I have been in a number of rural and semi-rural areas, including until recently my home on the outskirts of Bellevue, WA, where crosstalk gets worse as the weather gets wetter.) and (b) misadjusted transmission levels, that is, cases in which a signal is transmitted too loudly, such that the signal coupled to adjacent pairs rises noticably above the thermal noise floor. Cables in which pairs carrying modem signals are operated at the same transmission levels as those carrying voice signals are liable to exhibit crosstalk problems. Good design practice calls for setting data lines at a lower transmission level than voice lines, precisely in order to avoid crosstalk. These days, there are a lot of people (myself included) who operate modems over voice lines, which may explain some reports of crosstalk problems. This phenomenon can work both ways. There seems to be an interoffice trunk somewhere along the most common path between the 641 exchange (south and east Bellevue) and the 525 exchange (University district, Seattle) here in 206 on which the transmission level is set so low that I had to resort to manually connecting my autodial modem when dialing in from home, because the modem couldn't find the carrier from the answering modem in Seattle. Jeff Carroll carroll@atc.boeing.com
wally@cse.ogi.edu (09/16/90)
In Telecom-Digest: Volume 10, Issue 643, Message 1 of 8) carroll@ beaver.cs.washington.edu (Jeff Carroll) writes: > .... Just running four wires can cause all kinds of undesirable > electromagnetic coupling between wires that aren't supposed to couple. ... I remember asking a telephone lineman when I was 10 years old or so, why open wire (in rural areas) sometimes criss-crossed. He said it was to prevent crosstalk and went on to explain how crosstalk occurs. At that time, it was a new concept for me, and I began to notice crosstalk EVERYWHERE! (Anyone remember how bad crosstalk was for, say a 200-mile toll call in 1966?) Wally Kramer Step Technology, Inc. +1 503 244 1239 ...tektronix.tek.com!percy!steptech!wally
libove@libove.det.dec.com (Jay Libove) (09/19/90)
In article <11803@accuvax.nwu.edu> sherpa!rac@uunet.uu.net (Roger Cornelius) writes: >When I had my second line installed, I specifically requested a >completely separate line coming off the pole because I had heard of >problems like the above. The phone company didn't seem to mind, and >there was no additional charge either. Some months later, someone >pointed out that once my two lines connect to the pole, they're >connected back to a single line -- with everyone else's in the >neighborhood to boot. Makes sense to me, but then I know next to >nothing about phone systems. Interesting. I was told that if I wanted not only the amazingly huge and complex (put in a wall plate, yeah right, could've done it myself EXCEPT that my apartment complex didn't want to let me f*** with THEIR wires) but also wanted to actually make them do work and install another whole wire, I'd pay for all of the time (well, at least I'd have gotten a little more for my money) and equipment involved. Given that the network interface box on the building was a good hundred or more feet from where the wire would have to enter my apartment, I took my chances on sharing the existing four-wire line for two phone lines, rather than pay even more. Now I'm sorry about it, since I do get crosstalk. It just seem stupid that, now that we "own" the wires between the network interface unit and our phones, the phone company gets off providing unacceptable service just because that's typical. If I want another phone line, I should get another phone _line_ - the standard shouldn't be to mix and match signals in a known unclean electronic fashion. Jay Libove libove@libove.det.dec.com Digital Equipment Corporation decwrl!libove.det.dec.com!libove Detroit ACT/Ultrix Resource Center Opinions? They're mine, mine, all mine! Farmington Hills, Michigan and D.E.C. Can't have 'em!