sichermn@beach.csulb.edu (Jeff Sicherman) (11/16/90)
Due to complaints from roommates, I will finally be activating a second phone line to use my modem on. However, I will be using the existing 4-wire lines already built-in to the place, not able to add twisted-pair as is often recommended to avoid cross-talk with the voice line. Is there anything else I can do - some kind of external at the connector or something - to minimze this. I would rather not have to replace the modem, but in a pinch if it becomes a real problem, what would be necessary ? MNP I presume. Is this likely to *really* be a significant problem or is it mostly theoretical and sporadic ? Jeff Sicherman
tnixon@hayes.uucp (Toby Nixon) (11/16/90)
In article <1990Nov15.193826.3875@beach.csulb.edu>, sichermn@beach.csulb.edu (Jeff Sicherman) writes: > Due to complaints from roommates, I will finally be activating a > second phone line to use my modem on. However, I will be using the > existing 4-wire lines already built-in to the place, not able to add > twisted-pair as is often recommended to avoid cross-talk with the > voice line. Is there anything else I can do - some kind of external > at the connector or something - to minimze this. > > I would rather not have to replace the modem, but in a pinch if it > becomes a real problem, what would be necessary ? MNP I presume. > > Is this likely to *really* be a significant problem or is it > mostly theoretical and sporadic ? I've used modems on second lines connected through the yellow/black pair in a residence (actually, several different residences) and never had a problem. Remember -- as soon as that phone cable leaves your house, it immediately goes into a big fat cable with literally hundreds or thousands of other pairs of copper wire. If "crosstalk" was going to be a problem, you'd have already run into it!! -- Toby Nixon, Principal Engineer | Voice +1-404-449-8791 Telex 151243420 Hayes Microcomputer Products Inc. | Fax +1-404-447-0178 CIS 70271,404 P.O. Box 105203 | UUCP uunet!hayes!tnixon AT&T !tnixon Atlanta, Georgia 30348 USA | Internet hayes!tnixon@uunet.uu.net
floyd@hayes.ims.alaska.edu (Floyd Davidson) (11/19/90)
In article <2983@hayes.uucp> tnixon@hayes.uucp (Toby Nixon) writes: >In article <1990Nov15.193826.3875@beach.csulb.edu>, >sichermn@beach.csulb.edu (Jeff Sicherman) writes: > >> Due to complaints from roommates, I will finally be activating a >> second phone line to use my modem on. However, I will be using the >> existing 4-wire lines already built-in to the place, not able to add >> twisted-pair as is often recommended to avoid cross-talk with the >> voice line. Is there anything else I can do - some kind of external >> at the connector or something - to minimze this. >> [...] > >I've used modems on second lines connected through the yellow/black >pair in a residence (actually, several different residences) and >never had a problem. > >Remember -- as soon as that phone cable leaves your house, it >immediately goes into a big fat cable with literally hundreds or >thousands of other pairs of copper wire. If "crosstalk" was going >to be a problem, you'd have already run into it!! > Jeff you won't have any trouble at all *if* your current 4-wire drop wire is the usual j-k drop line that Toby is refering to above (with a red/green pair and a yellow/black pair). Each of those is a twisted pair. If you have a 6-wire drop line it may also have a blue/white pair that can be used also. If by some chance you have house wiring that is not twisted pairs on those lines, then you will have trouble. How much depends on how ling the lines are (how much is not twisted pair). It will probably not cause your modem any trouble at all, but the voice conversation on the other line may notice your modem. Just try it and see what happens. If things don't go right, which is unlikely, post something here giving as much detail as possible about the physical setup. Floyd -- Floyd L. Davidson floyd@hayes.ims.alaska.edu floydd@chinet.chi.il.us Salcha, AK 99714 connected by paycheck to Alascom, Inc. When *I* speak for them, one of us will be *out* of business in a hurry.
dave@westmark.WESTMARK.COM (Dave Levenson) (11/20/90)
In article <2983@hayes.uucp>, tnixon@hayes.uucp (Toby Nixon) writes: > Remember -- as soon as that phone cable leaves your house, it > immediately goes into a big fat cable with literally hundreds or > thousands of other pairs of copper wire. If "crosstalk" was going > to be a problem, you'd have already run into it!! No, not exactly. The big fat cable has individual twisted pairs which are all twisted in such as way as to cancel the crosstalk which would otherwise be created by induction between them. The original question was concerned with running two voice-frequency circuits (one of which happened to be used by a modem) in the same piece of quad. Quad has four wires, with no twists, and no anti-crosstalk arrangement. Crosstalk does occur in such cables, but it doesn't become noticable until the cable length approaches a hundred feet or so. (An admittedly subjective measurement ... your mileage may vary.) -- Dave Levenson Internet: dave@westmark.com Westmark, Inc. UUCP: {uunet | rutgers | att}!westmark!dave Warren, NJ, USA AT&T Mail: !westmark!dave [The Man in the Mooney] Voice: 908 647 0900 Fax: 908 647 6857
root@zswamp.fidonet.org (Geoffrey Welsh) (11/20/90)
Toby Nixon (tnixon@hayes.uucp ) wrote: >If "crosstalk" was going >to be a problem, you'd have already run into it!! I *do* run into crosstalk here at zswamp. The modem line runs down the black/yellow pair around my voice line, and I can hear - and so can the other party on the line - DTMF codes and carriers from the other line. Of course, these are many deciBels below the conversation, so they're not interfering and I expect that they'd be even less significant if I were speaking, as another modem would, much louder. Still, I can't help but wonder if, under certain marginal conditions, that crosstalk might be the difference between a usable connection and a noisy one. -- UUCP: watmath!xenitec!zswamp!root | 602-66 Mooregate Crescent Internet: root@zswamp.fidonet.org | Kitchener, Ontario FidoNet: SYSOP, 1:221/171 | N2M 5E6 CANADA Data: (519) 742-8939 | (519) 741-9553 MC Hammer, n. Device used to ensure firm seating of MicroChannel boards Try our new Bud 'C' compiler... it specializes in 'case' statements!
floyd@hayes.ims.alaska.edu (Floyd Davidson) (11/20/90)
In article <1546@westmark.WESTMARK.COM> dave@westmark.WESTMARK.COM (Dave Levenson) writes: >In article <2983@hayes.uucp>, tnixon@hayes.uucp (Toby Nixon) writes: > >> Remember -- as soon as that phone cable leaves your house, it >> immediately goes into a big fat cable with literally hundreds or >> thousands of other pairs of copper wire. If "crosstalk" was going >> to be a problem, you'd have already run into it!! > >No, not exactly. The big fat cable has individual twisted pairs >which are all twisted in such as way as to cancel the crosstalk >which would otherwise be created by induction between them. I'm not clear on what you meant by "all twisted", so here is a little more: Each pair is twisted. Other than that the only placement or arrangement done is to make it easy to identifiy which is which. >The original question was concerned with running two voice-frequency >circuits (one of which happened to be used by a modem) in the same >piece of quad. Quad has four wires, with no twists, and no >anti-crosstalk arrangement. Crosstalk does occur in such cables, >but it doesn't become noticable until the cable length approaches a >hundred feet or so. (An admittedly subjective measurement ... your >mileage may vary.) Agreed on the distance and the variation. What I do wonder about is what kind of quad this is that is not twisted. I don't work with cpe or outside plant other than my own home. But the stuff I buy at radio shack is twisted pair (3 pair, not quad) and the quad jk we use on PBX extentions at work is twisted pair. I really can't imagine running inhouse cabling that is not twisted pair. We sure don't put anything on a distribution frame longer than about 6 inches that is not twisted pair (it has to be on the same block, or it is twisted pair). Take a look at some of that non-twisted quad and see if it doesn't really have a twist about every 1-2 feet. Floyd -- Floyd L. Davidson floyd@hayes.ims.alaska.edu Salcha, AK 99714 paycheck connection to Alascom, Inc. When I speak for them, one of us will be *out* of business in a hurry.
grr@cbmvax.commodore.com (George Robbins) (11/21/90)
In article <1546@westmark.WESTMARK.COM> dave@westmark.WESTMARK.COM (Dave Levenson) writes: > In article <2983@hayes.uucp>, tnixon@hayes.uucp (Toby Nixon) writes: > > > Remember -- as soon as that phone cable leaves your house, it > > immediately goes into a big fat cable with literally hundreds or > > thousands of other pairs of copper wire. If "crosstalk" was going > > to be a problem, you'd have already run into it!! > > No, not exactly. The big fat cable has individual twisted pairs > which are all twisted in such as way as to cancel the crosstalk > which would otherwise be created by induction between them. > > The original question was concerned with running two voice-frequency > circuits (one of which happened to be used by a modem) in the same > piece of quad. Quad has four wires, with no twists, and no > anti-crosstalk arrangement. Crosstalk does occur in such cables, > but it doesn't become noticable until the cable length approaches a > hundred feet or so. (An admittedly subjective measurement ... your > mileage may vary.) I'm curious about this "quad" - normal "station cable" which is what they use to wire up houses and the like *does* consist of twisted pairs, normally two of them: yellow-black and green-red. Newer commercial wiring tends towards 3 or 4 pairs. In any case it would take a considerable amount of crosstalk to cause problems either way. The real concern is when there exits only one two-wire cicuit and the phone company uses special "carrier" equipment to multiplex a second circuit rather than route additional wires... -- George Robbins - now working for, uucp: {uunet|pyramid|rutgers}!cbmvax!grr but no way officially representing: domain: grr@cbmvax.commodore.com Commodore, Engineering Department phone: 215-431-9349 (only by moonlite)
floyd@hayes.ims.alaska.edu (Floyd Davidson) (11/21/90)
In article <15994@cbmvax.commodore.com> grr@cbmvax.commodore.com (George Robbins) writes: >In article <1546@westmark.WESTMARK.COM> dave@westmark.WESTMARK.COM (Dave Levenson) writes: >> In article <2983@hayes.uucp>, tnixon@hayes.uucp (Toby Nixon) writes: >> >> > Remember -- as soon as that phone cable leaves your house, it >> > immediately goes into a big fat cable with literally hundreds or >> > thousands of other pairs of copper wire. If "crosstalk" was going >> > to be a problem, you'd have already run into it!! >> >> No, not exactly. The big fat cable has individual twisted pairs >> which are all twisted in such as way as to cancel the crosstalk >> which would otherwise be created by induction between them. >> >> The original question was concerned with running two voice-frequency >> circuits (one of which happened to be used by a modem) in the same >> piece of quad. Quad has four wires, with no twists, and no >> anti-crosstalk arrangement. Crosstalk does occur in such cables, >> but it doesn't become noticable until the cable length approaches a >> hundred feet or so. (An admittedly subjective measurement ... your >> mileage may vary.) > >I'm curious about this "quad" - normal "station cable" which is what >they use to wire up houses and the like *does* consist of twisted pairs, >normally two of them: yellow-black and green-red. Newer commercial >wiring tends towards 3 or 4 pairs. > Despite what others are saying about "quad", you are correct, it does have a twist. There is a terminology problem here, but to a telco person "quad" means two twisted pair as opposed to "spiral four" which is also twisted, but all four together, with opposite wire forming each pair. There are many variations on the "twist", and in the case of drop wire it is going to be a very long twist. That is why people are looking right at it and thinking it is not twisted. Strip it back a couple feet and they will see that in fact it is. A shorter twist makes a bulkier cable, so it is avoided if possible. Even the cord to the hand set has a twist... Floyd PS Alascom, Inc. is the regulated ld carrier in Alaska, just as ATT is in the lower-48. We are the only two regulated ld carriers, and we do NOT compete with each other. -- Floyd L. Davidson floyd@hayes.ims.alaska.edu Salcha, AK 99714 paycheck connection to Alascom, Inc. When I speak for them, one of us will be *out* of business in a hurry.
urlichs@smurf.sub.org (Matthias Urlichs) (11/21/90)
In comp.dcom.modems, article <1990Nov20.131818.28875@hayes.ims.alaska.edu>, floyd@hayes.ims.alaska.edu (Floyd Davidson) writes: < In article <1546@westmark.WESTMARK.COM> dave@westmark.WESTMARK.COM (Dave Levenson) writes: < > < >[...] The big fat cable has individual twisted pairs < >which are all twisted in such as way as to cancel the crosstalk < >which would otherwise be created by induction between them. < < Each pair is twisted. Other than that the only placement or < arrangement done is to make it easy to identifiy which is which. < One other "arrangement" is usually done: each twisted pair has a different number of twists per length, to avoid two pairs being "twisted in sync" which may still allow crosstalk. (Or at least the cables I have are manufactured this way.) -- Matthias Urlichs -- urlichs@smurf.sub.org -- urlichs@smurf.ira.uka.de /(o\ Humboldtstrasse 7 - 7500 Karlsruhe 1 - FRG -- +49+721+621127(0700-2330) \o)/
floyd@hayes.ims.alaska.edu (Floyd Davidson) (11/21/90)
In article <ye^gg2.28@smurf.sub.org> urlichs@smurf.sub.org (Matthias Urlichs) writes: >In comp.dcom.modems, article <1990Nov20.131818.28875@hayes.ims.alaska.edu>, > floyd@hayes.ims.alaska.edu (Floyd Davidson) writes: >< In article <1546@westmark.WESTMARK.COM> dave@westmark.WESTMARK.COM (Dave Levenson) writes: >< > >< >[...] The big fat cable has individual twisted pairs >< >which are all twisted in such as way as to cancel the crosstalk >< >which would otherwise be created by induction between them. >< >< Each pair is twisted. Other than that the only placement or >< arrangement done is to make it easy to identifiy which is which. >< >One other "arrangement" is usually done: each twisted pair has a different >number of twists per length, to avoid two pairs being "twisted in sync" which >may still allow crosstalk. >(Or at least the cables I have are manufactured this way.) > On larger cables (not "quad") every pair in each bundle has a different length to the twist. And they are laid into the bundle in such a way that pairs with the closest twist are less likely to be physically next to each other. I am not positive that quad is not done the same way, but I've never seen anything saying it was (or wasn't for that matter). My point was that "quad" is twisted pair cable. With that said I'll through another one in on the subject of crosstalk on modem lines. Consider the fact that every extention line run off in a different direction from your demark point is *unterminated* when the phone or modem at the end of it is on-hook. If these stub lines are very short or very long they don't make any difference, but there is some point in between (I'd have to guess at what a significant length would be) that unterminated line is going to cause all kinds of problems. Comments??? Floyd -- Floyd L. Davidson floyd@hayes.ims.alaska.edu Salcha, AK 99714 paycheck connection to Alascom, Inc. When I speak for them, one of us will be *out* of business in a hurry.
urlichs@smurf.sub.org (Matthias Urlichs) (11/22/90)
In comp.dcom.modems, article <1990Nov21.140128.28529@hayes.ims.alaska.edu>,
floyd@hayes.ims.alaska.edu (Floyd Davidson) writes:
<
< With that said I'll throw another one in on the subject of crosstalk
< on modem lines. Consider the fact that every extention line run off
< in a different direction from your demark point is *unterminated* when
< the phone or modem at the end of it is on-hook. [...]
<
< Comments???
<
Yes -- don't have extensions on modem lines.
They are going to be wasting hours of your time when you try to find out why
the carier gets dropped at irregular intervals, while people complain
to your company's operator about the screeching noise on their phones. :-(
--
Matthias Urlichs -- urlichs@smurf.sub.org -- urlichs@smurf.ira.uka.de /(o\
Humboldtstrasse 7 - 7500 Karlsruhe 1 - FRG -- +49+721+621127(0700-2330) \o)/bill@unixland.uucp (Bill Heiser) (11/22/90)
In article <15994@cbmvax.commodore.com> grr@cbmvax.commodore.com (George Robbins) writes: >problems either way. The real concern is when there exits only one >two-wire cicuit and the phone company uses special "carrier" equipment >to multiplex a second circuit rather than route additional wires... > Can this really be done? Would it work with modems? Where I live, I want to install additional lines, but the persnickety condo people won't allow it ... grrr! -- home: ...!{uunet,bloom-beacon,esegue}!world!unixland!bill bill@unixland.uucp, bill%unixland.uucp@world.std.com Public Access Unix - Esix SYSVR3 - (508) 655-3848 other: heiser@world.std.com Public Access Unix (617) 739-9753