larry@kitty.UUCP.UUCP (03/13/87)
> I noticed that coming into our home that the plate with outside wires had > red and green connected to two posts and that the wire going to the phone had > the green connected to the red and the red connected to the green. Does this > matter? (ie is the line polarized or does it just act like two wires with > A/C electricity. Thanks in advance A telephone line has polarity, since direct current is used to excite the telephone instrument. Such excitation not only powers the telephone transmitter (i.e., microphone), but operates any DTMF (i.e., Touch-tone) dial circuit, dial pulsing circuit (in newer solid-state telephones), electronic tone ringer, solid-state network in newer telephones, etc. In addition, DC current flow through the telephone loop indicates to the central office apparatus that the telephone requests service and is in use (called loop signaling). While the telephone ringing signal sent from the central office is 20 Hz AC, the AC is superimposed upon a DC signal, so there is still always a DC potential present. The purpose of such superimposition is to assure immediate and reliable detection of called party answer ("ring trip"). The nominal on-hook (i.e., telephone is idle) DC voltage across a conventional telephone loop is -48 volts. Notice that I use the word "conventional", since a small but nevertheless significant percentage of telephone lines run through subscriber line concentrators or loop extenders; under these circumstances, the on-hook voltage can be as little as -6 volts DC or as high as -96 volts DC, depending upon the type of concentrator or loop extender apparatus. The vernacular used to describe telephone line polarity are the terms "tip" and "ring". The tip side of the line is in effect positive ground, and the ring side of the line is in effect a negative battery voltage (i.e., - 48 volts DC). While I have called the tip side of the line a "positive ground", it is not a true ground since the actual ground connection occurs in the central office apparatus through the DC resistance (typically 200 ohms) of an inductor or transformer winding. As a result, the on-hook measurement of the tip side of the line to an earth ground (i.e., water pipe) at the subscriber location will show a small voltage differential. On-hook measurement of the ring side of the line to earth ground at the subscriber location will show the nominal -48 volts. The following are some common equivalent designations for the tip and ring polarity of a telephone subscriber line: DESIGNATION TIP RING NOTES green wire of green/red pair X red wire of green/red pair X black wire of black/yellow pair X #1 yellow wire of black/yellow pair X #1 white wire of white/blue pair X #2 blue wire of white/blue pair X #2 white wire of white/orange pair X #3 orange wire of white/orange pair X #3 L1 terminal in telephone set X L2 terminal in telephone set X +T terminal in telephone set X #4 -T terminal in telephone set X #4 NOTE 1: When used as pair for second telephone line in 4-wire cable NOTE 2: White is equivalent to white wire with blue stripes, and blue is equivalent to blue wire with white stripes when striped cable is used. NOTE 3: White is equivalent to white wire with orange stripes, and orange is equivalent to orange wire with white stripes when striped cable is used; typically used for second telephone line in a multi-pair cable. NOTE 4: Common designation for GTE/Automatic Electric telephones Most telephones manufactured today are polarity independent; i.e., the telephone will work even if tip and ring are reversed. However, not all telephones are polarity independent; two notable exceptions are: telephones used for multi-party lines (which are fortunately disappearing!); and older Touch-tone telephones (whose dial won't work if tip and ring are reversed. Even though most telephones are polarity-independent, it is still a good idea to maintain correct color/terminal polarity in any telephone wiring. Why? Because it will simplify troubleshooting. As an example, say you experience a loud hum on your telephone line; a typical cause is either tip or ring accidentally shorted to earth ground. If you remove your telephone instruments from their jacks, and isolate the inside wiring from the outside line, using an ohmmeter you can determine which wire is shorted to ground. If you detect ground leakage on say, the tip side of the line, you will know exactly which color of wire and which terminal is to be suspect throughout the entirety of your inside wiring. Maintaining proper tip/ring polarity on all outside cables is very important to the telephone company, since various kinds of test equipment and procedures used from the central office can pinpoint the precise location of a cable fault; an important assumption for many of these fault-locating procedures is that the outside cables always have tip/ring correspondence. <> Larry Lippman @ Recognition Research Corp., Clarence, New York <> UUCP: {allegra|ames|boulder|decvax|rocksanne|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231 {hplabs|ihnp4|mtune|seismo|utzoo}!/ <> FAX: 716/741-9635 {G1,G2,G3 modes} "Have you hugged your cat today?"
natkin@DEGAS.BERKELEY.EDU (Michael Natkin) (03/18/87)
In article <8703130415.AA22972@seismo.CSS.GOV> larry@kitty.UUCP writes: > Maintaining proper tip/ring polarity on all outside cables is very >important to the telephone company, since various kinds of test equipment >and procedures used from the central office can pinpoint the precise location >of a cable fault; an important assumption for many of these fault-locating >procedures is that the outside cables always have tip/ring correspondence. > ><> Larry Lippman @ Recognition Research Corp., Clarence, New York I've always wanted to know how the locating of cable faults works - i have some hypotheses, but maybe you would care to edify myself and other readers on this subject? michael natkin natkin@degas.berkeley.edu
JSOL@XX.LCS.MIT.EDU (Jon Solomon) (03/18/87)
I noticed when my lines were installed, they had a break in my subscriber loop and they found it by using a buzzer on the line which they tested for using a probe connected to their butt-in set. It was fun to watch. --jsol -------
gary%percival%reed@tektronix.tek.COM.UUCP (03/20/87)
There are several methods used by the telco's for line testing. The simplest is that all cables have a known (very precisely) resistance and capacitance per foot. If a short is applied at the end of a cable (or a known resistance, etc), then a calibrated ohmmeter can tell you how far away the short is. If you are looking at a clean open, you can apply the same principle with a capacitance meter (though, in practice, it is not as accurate). By knowing WHAT is hanging on the end of your cable, you can quickly tell the status of the pair AND the station. This is why the telco's fought so hard about registration. They really didn't care about the equipment, they just need to know what it "looks" like, for trouble isolation purposes.
larry@kitty.UUCP.UUCP (03/20/87)
Subject: Re: color code for wire? In a recent reply to my original article, rdsnyder@MIT-CCC writes: > > DESIGNATION TIP RING NOTES > > green wire of green/red pair X > > red wire of green/red pair X > > black wire of black/yellow pair X #1 > > yellow wire of black/yellow pair X #1 > > > > NOTE 1: When used as pair for second telephone line in 4-wire cable > > The yellow/black pair above is reversed. > Yellow is TIP of the second pair in quad (4 cond. Gr/Rd/Yl/Bk cable) and > black is RING of the second pair. Sorry, but you are incorrect. Black is always TIP and yellow is always RING. This true not only for inside station wiring, but for outside direct burial two-pair "B" Service Wire. I refer to AT&T System Practices Sections 461-610-100 and 460-300-143 as examples in case anyone doubts my statement. You may be confused by looking at the end of a modular plug and thinking that TIP is one side of center, and RING is the other; the pin locations on modular connectors are transposed every other pair (up to the full 4-pairs for an RJ-45). > The yellow/black pair is also used in key systems as the A/A1 pair. The > station equipment shorts A & A1 together while off-hook. In this application, the A-lead is the actual control line, and the A1-lead is ground. The A-lead is always the "tip" conductor and the A1-lead is always the "ring" conductor, when the two are in the same pair. > White, red, black, yellow and violet are tip, and blue, orange, green, > brown, and slate are ring. Except, of course, when white/red, white/black, and yellow/red is used for distributing frame jumper pairs... :-) <> Larry Lippman @ Recognition Research Corp., Clarence, New York <> UUCP: {allegra|ames|boulder|decvax|rocksanne|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231 {hplabs|ihnp4|mtune|seismo|utzoo}!/ <> FAX: 716/741-9635 {G1,G2,G3 modes} "Have you hugged your cat today?"
larry@kitty.UUCP (03/22/87)
In a recent article EXT1.CHAIKLIN@CU20B.COLUMBIA.EDU (Seth Chaiklin) writes: > I am interested in installing a hunter on three telephone lines that are > attached to modems that are receiving calls. The phone company tells me > that the lines are "auxiliary" lines and that one cannot put a hunter > on these lines. They claim that a "trunk" line is needed if one wants > to use a hunter. > What is the difference between an auxiliary line and a trunk line? In virtually all cases, the difference is in telephone company tariff descriptions, and therefore in the recurring monthly cost for the affected line; there is no "hardware" difference. Trunks, auxiliary lines, and POTS lines (Plain Old Telephone Service) all look the same to the central office line equipment; the only exception is that trunks are often configured as ground-start lines - but then again, ANY line can be optioned as a ground-start line. With the exception of constraints imposed by older electromechanical central offices (like SxS and X-Y), virtually any central office can be configured to cause any directory number to "hunt" (if busy) to any other directory number, in a continuing chain (often called ISG - Incoming Service Group) without regard to the actual directory numbers involved. There is no special hardware in the central office which must be added to cause lines to hunt; in electromechanical offices, jumper wires are changed in some cross-connect fields. In ESS offices, hunting configuration is accomplished through software changes made using the console tty. > Are the phone company claims accurate? It depends upon the tariffs for your local telephone company. For New York Telephone, auxiliary lines and auxiliary trunks (yes, there is a "paper" distinction) can be made to hunt in additional groups (i.e., in addition to the "main directory number" hunt group) for no additional monthly charge; there is, however, a non-recurring "installation" charge if this configuration is performed at some time after the lines in question are actually installed. However, some telephone company tariffs require that the FIRST line of any hunt group be considered a "trunk" or "main" line - at a higher recurring monthly cost. This may be your situation; if it is, you will face a monthly increase in the charge for the first affected line, plus a non-recurring charge for the new configuration. No physical line change nor premises visit will be involved. (Read "rip-off", if you so desire... :-) ) I would suggest that you ask your telephone company salesperson to put in writing the billing charges for the addition of hunting; this request generally causes a telephone company salesperson to double-check their information. <> Larry Lippman @ Recognition Research Corp., Clarence, New York <> UUCP: {allegra|ames|boulder|decvax|rocksanne|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231 {hplabs|ihnp4|mtune|seismo|utzoo}!/ <> FAX: 716/741-9635 {G1,G2,G3 modes} "Have you hugged your cat today?"
larry@kitty.UUCP (03/22/87)
In a recent article natkin@DEGAS.BERKELEY.EDU (Michael Natkin) writes: > > Maintaining proper tip/ring polarity on all outside cables is very > > important to the telephone company, since various kinds of test equipment > > and procedures used from the central office can pinpoint precise location > > of a cable fault; an important assumption for many of these fault-locating > > procedures is that the outside cables always have tip/ring correspondence. > > I've always wanted to know how the locating of cable faults works - > i have some hypotheses, but maybe you would care to edify myself and > other readers on this subject? There are a number of fault-locating methods used by operating telephone companies (and others who maintain long runs of cable); these methods have in common that measurements are taken from one or both ends of the cable only - with the location of the fault between the two locations being the result of the measurement. Fault location in telephone cable is not as simple as just making resistance or capacitance measurements. One of the reasons is that there is often a foreign potential present across tip-to-ring, tip-to-ground, and ring-to-ground. Depending upon the type of fault (like a wet cable splice), all three of these measurements may be different. What this means is that a simple ohmmeter circuit or simple two-terminal Wheatstone bridge is useless since these resistance measurement techniques will be seriously in error when made in the presence of a foreign potential. As a result, various other bridge measurements have been developed over the years; many of these are three-terminal measurements which are also made to ground in order to compensate for the presence of foreign potentials on the suspect pair. Examples of these techniques are the Varley Loop, Murray Loop, Fisher Loop, Moody Loop and Hilborn loop. Some of the above procedures also require the use of pairs in the same cable which are known to be good (like the Moody Loop). All of the above methods are used with DC bridge excitation and measure the location of crosses (conductor-to-conductor) and grounds (conductor-to-ground). Some of the above methods are used with AC bridge excitation (like the Murray Loop) and can therefore measure the location of open pairs and the presence of "split" pairs (caused by an incorrect splice). The selection of the actual test method is generally based upon the preference and experience of the craftsperson making the test. A fault location test on a bad pair will generally begin as follows: 1. Isolate pair from apparatus at both ends, and "cord" pair to a test position in the central office. 2. Measure voltage from: tip-to-ring, tip-to-ground, ring-to-ground, tip-to-battery and ring-to-battery. Test battery voltage is usually a current-limited -48 volts, but other test voltages are also used. 3. If there is little foreign potential (a good craftsperson knows the difference between actual potential and momentary potential caused by capacitive charging of the subject cable pair) in the above measurements, it is safe to assume that fault is either an open or a cross, and is isolated from ground. Measure resistance from tip-to-ring using a simple Wheatstone bridge circuit. If there is a cross (i.e., the pair is open, so anything less than normal leakage resistance is a cross), use the resistance measurement with a circuit layout card (shows path, cable gauges, loading, and distance from central office) and calculate location of short based upon knowing the actual resistance of the cable from the central office to any point. If the resistance is high (like normal leakage resistance, >> 100 K ohms), have craftsperson at other end of line short pair from tip-to-ring. Measure resistance using Wheatstone bridge circuit. If resistance is the expected loop resistance, then pair looks good for tip-to-ring DC continuity, but may have leakage to ground. If resistance is still high, then pair is open. If pair is open, then measure capacitance using bridge in Murray Loop configuration with AC excitation (or use capacitive "kick" method of foreign potential measurement - if you want to be crude about it). Using capacitance measurement and known capacitance of cable, determine the distance of the "good" section of the pair under test. All outside telephone cable, regardless of wire gauge - either polyethylene or paper insulted - is intentionally designed to give a known capacitance per foot; the most common value is 0.083 uF/loop-mile. 4. If there was significant foreign potential or the presence of a ground as detected in (2) above, then the situation gets hairy; now is the time to use some of the other bridge techniques mentioned above. The foreign potential currents (as opposed to voltages above) may be measured to get a handle on the cause of the foreign potential (usually a cross with another working pair). These bridge techniques may also require a craftsperson at the other end to selectively ground, cross, or connect the suspect pair to other pairs that are known to be good. 5. If a pair looks good from a DC standpoint, but still has transmission trouble, then capacitance measurements are taken from each wire in the pair to ground to see if it might be crossed with a wire from another pair, or have some other type of fault. Also, resistance measurements may be again applied, but with a high range in the order of the cable leakage resistance, to see if something is amiss. The above five steps are the "traditional" methods used by telephone companies, and are still used in the majority of test centers. Other (and at times better) techniques include: 1. Capacitance measurement through electronic means that are reasonably immune to foreign potentials on the pair under test. Direct-reading test sets have been available for a number of years that read fault distance directly in feet (you dial in the normal capacitance of the cable per unit length). For example, I have a Hewlett-Packard 4910-F open fault locator test set which has paid for itself many times over in locating cable faults; it will resolve down to _feet_. 2. Using a time-domain reflectometer (TDR, also sometimes called "sweep" testing) will give a good picture of a cable pair condition under many conditions. The TDR works by sending a short, high-energy pulse down a cable, and displaying the return echo on an oscilloscope display. Use of a TDR requires dialing in the dielectric constant of the cable (not a problem, usually) so that the normal propagation velocity of the cable is known. The display is calibrated directly in feet or meters, so that the precise location is the fault can be pinpointed. Poor splices, leakage to ground, etc. show up well on a TDR, along with any bridge taps. A TDR has some limitations, in that the measurement generally cannot pass through more than one loading coil. Most TDR's are used for coaxial cable measurement, but TDR's for twisted pairs are available from Biddle, Northeast Electronics, W&G Instruments, etc. 3. Sending an audio-frequency or VLF signal into a cable pair and following its progress using a hand-held receiver held in close proximity to the cable. This is obviously not too handy for faults which could be miles away :-), but it is inexpensive and useful for one-person use in the field where distances are relatively short. In summation, the above will give you some idea as to what is involved in cable-fault location; some of the procedures may form an outline for people reading this article to actually use themselves under the right circumstances. Overall, there is no magic procedure for cable-fault location, with the actual method being a matter of personal experience, discretion, and nature of the available fault-locating apparatus (not unlike writing a computer program :-). <> Larry Lippman @ Recognition Research Corp., Clarence, New York <> UUCP: {allegra|ames|boulder|decvax|rocksanne|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231 {hplabs|ihnp4|mtune|seismo|utzoo}!/ <> FAX: 716/741-9635 {G1,G2,G3 modes} "Have you hugged your cat today?"
schuster@dasys1.Dasys.COM.UUCP (03/29/87)
Recently I had occasion to call Sony Customer Service in NJ on their WATS
line (800-222-SONY). Prior to ringing, I was greeted by the following
telephone-company-sounding recorded message:
"Thank you for calling. For faster service please press or dial '1' _now_".
Does anyone know what this means? How will pressing '1' at that point give
me faster service? I was unable to discern any difference with or without.
l\ /l' _ Mike Schuster {allegra,philabs,cmcl2}!phri!dasys1!schuster
l \/ lll/(_ Big Electric Cat {bellcore,harpo,cmcl2}!cucard!dasys1!schuster
l lll\(_ New York, NY USA {philabs}!tg!dasys1!schusterlarry@kitty.UUCP.UUCP (04/05/87)
In a recent article, Werner Uhrig <CMP.WERNER@R20.UTEXAS.EDU> write: > > There are several methods used by the telco's for line testing. ..... > > By knowing WHAT is hanging on the end of your cable, > > you can quickly tell the status of the pair AND the station. > > This is why the telco's fought so hard about registration. They > > really didn't care about the equipment, they just need to know what it > > "looks" like, for trouble isolation purposes. The only reason that operating telephone companies sought apparatus registration was to assure themselves that no "harm" to the switched network would result from improperly designed apparatus. For example: apparatus which places signals of excessive amplitude on a telephone line can cause crosstalk on other working lines; apparatus which provides leakage current paths to ground can not only cause crosstalk (by creating a longitudinal unbalance on the cable pair), but can also upset automatic line insulation test apparatus into thinking that a cable fault exists; etc. The FCC Part 68 registration specifications were created to set a uniform standard of what was acceptable as telephone apparatus without creating trouble conditions for the operating telephone company. While a "ringer equivalence" specification may give a telephone company test bureau some idea as to the impedance terminating the subscriber by the connected devices, for all intents and purpose, the telephone company will never trust this information. If a cable problem presents itself, the telephone company will generally send a craftsperson into the field to open the pair at the subscriber location (or outside on a pole) before any test measurements are taken. The telephone company would be naive to believe what a customer reports as being their connected apparatus. > HMMMM, it's been years now that I've taken the trouble to tell SWB about the > latest changes in equipment that I've connected at my end - mainly, because > it changes often and because I'm under the impression that they don't really > care to know; or, at least, don't do anything with the information that I > give them about my latest set of hardware (besides, it often changes on > a daily basis; what with all these new modems, answering machines, phones and > other gadgets to test and play with :-) > > Now, what I'd like to know is the following: > > 1) Can someone tell me what the phone company *SHOULD* be doing with the data > describing my hardware? Nothing, really, other than making note of the FCC registration number on their "service billing record". Quite frankly, I have never known of an operating telephone company that even checked to see if the FCC registration number was a valid number for any piece of telephone apparatus. > 2) Is there something that I should *INSIST* that SWB do in response to me > reporting what I have connected? Nope. Assuming that you have given a "valid" FCC registration number, there is nothing that your operating telephone company can or will do, based upon the nature of the apparatus that you have connected to the telephone line. Your central office telephone loop will be designed according to some already-established plan created by a facilities engineer. There may be more than one plan in effect for a given central office, with the actual plan being selected by the available serving cable facilities between the central office and your location. For example, your line may run through a negative- impedance repeater to meet an office transmission goal; or, your line may run through a subscriber line concentrator if cable facilities are scarce; etc. As a further example, New York Telephone generally tries to limit subscriber loop loss to no more than 5.5 dB. Whatever combination of cable and/or repeater facilities are available will be used to achieve this goal. Subscriber lines for dial-up data use or PBX trunks are usually available with a lower loop loss - but at an ADDITIONAL COST. You get what you pay for - which means that for the price of a regular subscriber line you get no choice of anything and no special treatment. > 3) Is there some way that I can test that they *ACTUALLY DID* what needed to > be done at their end? Nope. Since they don't do anything, you can't very well test for it. :-) > 4) Can not reporting my latest set of hardware lead to *DEGRADING* in line > quality somehow? for example, could this lead to degraded line quality > for data communications using a modem (especially at 2400 baud)? or to > another phenomenon, such as "not all connected phones ring during an > incoming call"? You might degrade your telephone line by, say, connecting too many telephone sets with equipped ringers, but that is YOUR problem - not the telephone company's. The telephone company is not going to do anything - regardless of what you tell them. > I guess, what I really need is a pointer to a book which really all that I may > ever want to know about telephones and data-communications in a lingo I can > understand and make sense of (i.e. don't require the background and knowledge > of the lingo of a telecommunications engineer). Please, *DO* give pointers !! Unfortunately, I don't know of a good book that would fulfill your request. Books that I have seen are either: (1) insultingly simple, as written for Joe and Mary Consumer, or (2) deal in theory, and therefore fail to give immediate, practicable answers. However, rather than leave you empty-handed, a good middle-of-the-road book is "Telecommunications and the Computer", by James Martin, published by Prentice-Hall, ISBN 0-13-902494-8. <> Larry Lippman @ Recognition Research Corp., Clarence, New York <> UUCP: {allegra|ames|boulder|decvax|rocksanne|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231 {hplabs|ihnp4|mtune|seismo|utzoo}!/ <> FAX: 716/741-9635 {G1,G2,G3 modes} "Have you hugged your cat today?"
larry@kitty.UUCP.UUCP (04/05/87)
In a recent article PGW@XX.LCS.MIT.EDU (Paul G. Weiss) writes: > I had heard a rumor that if you have trouble getting through to a number > that is busy because of lots of callers (as opposed to one long conversation) > for example a movie theatre on a Friday evening, then you can get through > by dialing all the numbers but the last one, waiting about 20-30 seconds, > then dialing the last number. > > I've tried this a few times, and it seems to work! Now am I just getting > lucky or is there any reason why this should work? You were just lucky. In many central offices, hunting will only occur if you dial the FIRST (i.e., listed) number of an incoming service group. Dialing any other number will get you just that line - and no other if it is busy. Now, there is a grain of truth to getting through to certain places by dialing a "last" number. Many places that deal with the public reserve one or more numbers for "selected" people to call; these reserved numbers are never part of the incoming service group. These reserved numbers are, of course, unlisted numbers. However, the "last" number in what may appear to be a consecutively-numbered incoming service group may really be a separate line which is not part of that group. For example, say you have a business with five lines: 234-5600, 234-5601, 234-5602, 234-5603 and 234-5604. Only the first four lines form the incoming service group (5600 to 5603); 5604 is a private line for selected people who have to get through. So, dialing the 5604 number gets you through... Of course, there is no guarantee that the private line is the last number, but more often than not - it is. > [The best way I have found to get through on a radio station line is > to program their number into your speed calling and sit there with > one finger on the hookswitch and another almost pressing 9#. --jsol] You got it! <> Larry Lippman @ Recognition Research Corp., Clarence, New York <> UUCP: {allegra|ames|boulder|decvax|rocksanne|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231 {hplabs|ihnp4|mtune|seismo|utzoo}!/ <> FAX: 716/741-9635 {G1,G2,G3 modes} "Have you hugged your cat today?"
howard@cos.UUCP.UUCP (04/06/87)
One minor point (minor until it gets you): dial modems, especially the higher speed ones, may not work properly because the network interface device has resistors set for voice use, not data. It is worth letting your telco know you are running higher speed data, because your network interface should then be configured to give you better signal to noise ratios, not important for voice. If they're going to charge more for data access, do this only after you have unacceptable problems. Your problems, however, often are in the jack, not the local loop.