stevel@tybalt.caltech.edu (Steve Ludtke) (09/12/88)
A friend just presented me with an interesting question. He has an answering machine, and 2 phone lines. He wanted to know if he could just cross the two lines to get it to work on both. My immediate response was, of course not, that would really screw thing up. However the longer I thought about it the less certain I became. Since he wouldn't be dialing out while it was hooked up like this, that wouldn't be a problem. I don't know what a phone line will do if you send a ring signal over it. Anyone have any theories. I'm tempted to just try it, and see what happens. --------------------------------------------------------------------------- Steve Ludtke stevel@tybalt.caltech.edu ..!cit-vax!tybalt.caltech.edu!stevel stevel@citiago (Bitnet) OBS949 (Amer PPl lnk) 72335,1537 (Compuserve) XJM16487 (Genie)
lemke@Apple.COM (Steve Lemke) (09/12/88)
In article <7921@cit-vax.Caltech.Edu> stevel@tybalt.caltech.edu (Steve Ludtke) writes: >A friend just presented me with an interesting question. He has an answering >machine, and 2 phone lines. He wanted to know if he could just cross the >two lines to get it to work on both. My immediate response was, of course >not, that would really screw thing up. However the longer I thought about >it the less certain I became. Since he wouldn't be dialing out while it was >hooked up like this, that wouldn't be a problem. I don't know what a phone >line will do if you send a ring signal over it. Anyone have any theories. >I'm tempted to just try it, and see what happens. Well, I had a two line switch from Radio Shack that would automatically select the ringing line and send it to the answering machine (note that my thing was the older, $40.00 model, and now they have a simpler one for $20). Anyway, it also had buttons for line 1 and line 2 which would select which of the two lines would be used if the device was a phone and it was picked up to make a call. Anyway, someone once pushed both buttons accidentally, thus shorting the two lines together (this worked nicely for 3-way calls when we wanted to) with the phone on-hook. The box sat like this for a while, and then one day one of the lines was dead. The phone company said that since the lines present voltages on the other lines, (2 on 1 and vice-versa), line one dropped a "trouble card" at the office, and since they couldn't fix it from there, they disconnected it. Not a very good situation, and not some- thing I would recommend. Get the $20 box from RS and it will work fine. ===== Steve Lemke ===== Internet : lemke@apple.com UUCP: {sun,voder,nsc,decwrl}!apple!lemke AppleLink: LEMKE GEnie: S.Lemke All opinions are, of course, mine, and could never belong to anyone else!
cep4478@ritcv.UUCP (Christopher E. Piggott) (09/12/88)
I used to do this all the time, too, because I was too cheap to spring for the $12 three-way-calling custom feature installation. (Eventually, when they had a free hook-up deal on it, I got it - well worth the few dollars a month for the times I use it). Anyhow, crossing the lines caused a tremendous buzzing and relatively bad audio between L1 and L2 (while the guy who is doing the crossing hears and is heard rather normally). The interesting thing I wanted to share is that I tried dialing both lines (in touch tone) at the same time, and found that one line was consistently faster to connect than the other (i.e. the same line would always come up ringing, and the other busy, no matter what number I called, long distance or otherwise). From that day on, I always used the faster line when trying to win radio contests. (Every little bit helps - I won $30 worth of cheap perfume, but that's it so far). /Christopher
larry@kitty.UUCP (Larry Lippman) (09/13/88)
In article <7921@cit-vax.Caltech.Edu>, stevel@tybalt.caltech.edu (Steve Ludtke) writes: > A friend just presented me with an interesting question. He has an answering > machine, and 2 phone lines. He wanted to know if he could just cross the > two lines to get it to work on both. My immediate response was, of course > not, that would really screw thing up. However the longer I thought about > it the less certain I became. Since he wouldn't be dialing out while it was > hooked up like this, that wouldn't be a problem. I don't know what a phone > line will do if you send a ring signal over it. Anyone have any theories. In the on-hook (i.e., idle) state, connecting the two lines exactly in parallel (tip1-to-tip2 and ring1-to-ring2) will, in general, be undetected by the central office apparatus since there will be no current flow. In the on-hook state, connecting the two lines in parallel with reversed polarity (tip1-to-ring2 and ring1-to-tip2) is _guaranteed_ to create an off-hook condition for BOTH lines, rendering both lines inoperable for both incoming and outgoing calls (i.e., a permanent signal is created in the CO, along with an eventual trouble report). In the on-hook state with both lines connected in parallel, an incoming call will result in an immediate ring trip, resulting in no effective ringing signal to any customer apparatus. In most CO's the ring trip will momentarily pull dial tone on the other line, but then disconnect the incoming call. In some CO's both lines may be forced into a permanent signal - even though the incoming call has been terminated. In some ESS offices, an automatic trouble report may be generated - even if both lines do not lock up as a permanent signal. In the off-hook state with both lines connected in parallel, an outgoing call attempt will result in both lines pulling dial tone as a near-simultaneous event. Either rotary or DTMF dialing will most likely succeed in two near-simultaneous calls to the same number. If the CO traffic load is high (especially in an electromechanical office), resulting in one line being connected to a dial register more than a hundred milliseconds before the second line, chances are that a spurious rotary dial pulse will be created - thereby rendering effective dialing impossible on one or both lines. > I'm tempted to just try it, and see what happens. Try it if you like, but I can assure you that no useful result will occur. <> Larry Lippman @ Recognition Research Corp., Clarence, New York <> UUCP: {allegra|ames|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231 {att|hplabs|mtune|utzoo|uunet}!/ <> FAX: 716/741-9635 {G1,G2,G3 modes} "Have you hugged your cat today?"
raoul@eplunix.UUCP (Otero) (09/20/88)
In article <2689@kitty.UUCP>, larry@kitty.UUCP (Larry Lippman) writes: > In the on-hook (i.e., idle) state, connecting the two lines exactly > in parallel (tip1-to-tip2 and ring1-to-ring2) will, in general, be undetected > by the central office apparatus since there will be no current flow. No such luck. Unless the voltage matching is perfect, which it never is, a small DC current will flow from one line to the other. This will mess up both your lines, and you will not be able to use either. Ma Bell will also usually disconnect the lines within about a week of this sort of nonsense, thinking there is a short somewhere (there is!). However, don't take any of our word for it. Just short them together at the phone jack and see.... Try some real scientific method.
larry@kitty.UUCP (Larry Lippman) (09/27/88)
In article <657@eplunix.UUCP>, raoul@eplunix.UUCP (Otero) writes: > > In the on-hook (i.e., idle) state, connecting the two lines exactly in > > parallel (tip1-to-tip2 and ring1-to-ring2) will, in general, be undetected > > by the central office apparatus since there will be no current flow. > > No such luck. Unless the voltage matching is perfect, which it never is, > a small DC current will flow from one line to the other. This will > mess up both your lines, and you will not be able to use either. Ma > Bell will also usually disconnect the lines within about a week of this > sort of nonsense, thinking there is a short somewhere (there is!). With one rather rare exception (two lines, each on a dedicated loop-extender), for all intents and purposes there will be no detectable current flow if the two lines are connected in parallel when on-hook. CO switching apparatus must be able to operate in the presence of leakage resistance caused by cable insulation conductance (often aided by water!). In general, CO apparatus should be able to dial at maximum loop resistance (usually 1,500 ohms) with a "leak" of 50,000 ohms (1 mA of spurious current flow), and should not be able to pull dial tone with a 10,000 ohm leak (5 mA of current flow). At a typical maximum loop resistance of 1,500 ohms plus a maximum of 500 ohms station set resistance, one has at least 25 mA of current flow in order to pull dial tone. 5 mA of current flow is small, when compared to the minimum amount to dial in a normal situation. Typically, at least 5 mA of current is required before the CO apparatus will detect an off-hook condition. Bear in mind that this threshhold is intentional, so as to prevent spurious dial tone requests when outside cable plant is only "slightly wet". Assuming a situation "close" to the CO with two 250 ohm loops, for a 250 ohm ring-to-ring resistance, a CO battery voltage differential of 1.25 volts between each line relay (or current sensor) would be required. While this may seem like a small voltage differential, it really is quite large when comparted to CO power distribution critera. Good CO power distribution practice goes to great lengths using really large gauge wire to keep the impedance of the 48-volt battery distribution as low as possible; the primary reason reason is to minimize noise and crosstalk. Incidently, it is common to see a CO voltage of greater than 48 volts. Virtually all CO's use a 24-cell battery string, with a typical "float" voltage of 2.17 volts per cell, resulting in a nominal 52.08 volts. While a counter-EMF cell may be used to drop this float voltage (the counter-EMF cell is shorted when AC power fails), a battery voltage between 50 and 51 volts is most common. The battery voltage may even be a volt or two higher if an "equalizing" charge is being placed across the battery string. > However, don't take any of our word for it. Just short them together > at the phone jack and see.... Try some real scientific method. If you want to be real scientific about it, use a milliammeter to measure the current flow. One other exception to my statement above would be if the two lines were served by different exchanges using physically different switching apparatus within the same CO building (like XBAR and ESS); this is not uncommon in large cities with multiple exchanges in the same CO building. <> Larry Lippman @ Recognition Research Corp., Clarence, New York <> UUCP: {allegra|ames|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231 {att|hplabs|mtune|utzoo|uunet}!/ <> FAX: 716/741-9635 {G1,G2,G3 modes} "Have you hugged your cat today?"
pozar@hoptoad.uucp (Tim Pozar) (09/27/88)
raoul@eplunix.UUCP (Otero) wrote: > In article <2689@kitty.UUCP>, larry@kitty.UUCP (Larry Lippman) writes: > > In the on-hook (i.e., idle) state, connecting the two lines exactly > > in parallel (tip1-to-tip2 and ring1-to-ring2) will, in general, be undetected > > by the central office apparatus since there will be no current flow. > > No such luck. Unless the voltage matching is perfect, which it never is, > a small DC current will flow from one line to the other. This will > mess up both your lines, and you will not be able to use either. Ma > Bell will also usually disconnect the lines within about a week of this > sort of nonsense, thinking there is a short somewhere (there is!). > > However, don't take any of our word for it. Just short them together > at the phone jack and see.... Try some real scientific method. Or the way I've always done it was via a transformer... t1 ----- ----- t2 )||( 600 ohms )||( 600 ohms )||( r1 ----- ----- r2 -- ...sun!hoptoad!\ Tim Pozar >fidogate!pozar Fido: 1:125/406 ...lll-winken!/ PaBell: (415) 788-3904 USNail: KKSF / 77 Maiden Lane / San Francisco CA 94108