larry@kitty.UUCP.UUCP (05/11/87)
I thought the following two articles might be of interest to those who do not read or archive the groups to which they were posted: >From postnews Sat May 9 00:15:58 1987 Subject: Re: Phone Line Quality Newsgroups: comp.dcom.modems Summary: More on noise and other topics... References: <9728@decwrl.DEC.COM> In article <9728@decwrl.DEC.COM>, nourse@nac.dec.com (Andy Nourse) writes: > > ... the transmission loss on most interoffice trunks originating at End > > Offices (Class 5) trunks is carefully kept below 4.0 dB... > > Toll Center (Class 4) and up... below 2.6 dB > > a reasonably flat transmission characteristic between 300 and 3,000 Hz. > What are the specs for signal-to-noise ratio? If I want to call out of > the three-small-town local calling area, I have to dial 1 <CLACK!!><HISSSSSSS> > which routes the call out to Leominster, 15 miles away. Voice communication channels usually have a minimum of 30 dB as a signal-to-noise ratio. This may be surprising, but data channels can usually get away with a _lower_ S/N ratio minimum, typically 15 dB. Other parameters, such as phase shift (envelope delay distortion) are far more critical on data circuits than S/N ratio. It sounds to me like your central office has some bad N-carrier circuits (analog FDM), even more likely of the N1-variety which still uses vacuum tubes. N1 carrier requires continual maintenance to keep its circuits "in tune", and it sounds like someone has been remiss in this area. There is still an amazing amount of vacuum tube FDM carrier in service today. > > ... Trunks which fail to pass these automatic tests are disabled > > until repair is effected. > That must be why I sometimes get a fast busy, or drop back to a dial tone, > when i dial 1 (this is before I get to dial any other digits). I suppose > it can thus disable ALL the trunks. That does, of course, also affect > 0 (for Operator) and all paths to Repair Service. I did not mean to imply that automatic trunk testing is in use everywhere, although it is extensively implemented by AT&T Communications and the BOC's. Losing a large number of trunks though intentional disabling by automatic trunk test apparatus would be an unusual event, and would be rare and quickly attended to. It sounds more like switching apparatus trouble or traffic overload. Switching apparatus trouble which limits access to less than the allocated number of trunks is an insidious problem which is not easily diagnosed until customer complaints reach a level where a repairperson is eventually dispatched the CO and to get to the bottom of the problem. Automatic trunk test apparatus does NOT test connectivity to the trunks by the switching apparatus. If you are plagued with all trunk busy signals, complain to repair service - otherwise, they may never know about the problem! > > So the point is: under virtually all circumstances, > > you should have little concern about the transmission quality of interoffice > > trunks, as compared to your own subscriber loop. > Are old, rural, step-by-step exchanges an exception to this? > The noise starts when I dial 1, so I don't think the subscriber loop > has anything to do with it. Well, unfortunately older SxS offices usually have older carrier of the FDM variety (see above). FDM carrier requires continual maintenance. Well-maintained carrier should not present a noise problem (even N1 carrier); it sounds like your CO may be the victim of reduced maintenance manpower (to save money, of course!). > > ...some of this standardization has gone to hell with the advent of > > Alternate Long Distance carrier... > Some local operating companies (including ours) are using that as an excuse to > let line quality deteriorate, even for calls within the LATA. That's true. The telephone companies are also getting killed by increasing labor costs, so they reduce preventative maintenance, resulting in - voila! - poor transmission in some areas. Reduced maintenance is more common with independent operating telephone companies; AT&T and the BOC's predicted rising labor costs some years ago, and therefore developed and installed an extensive variety of automatic trunk test apparatus. The independent operating telephone companies have much less automatic trunk test apparatus than the BOC's and AT&T. > > the comparatively small additional monthly and installation charge is well > > worth it to get a better subscriber loop. > I just checked with New England Telephone. They said there is no such option. > In 1980, when I had a Bell 212a modem installed (with an RJ41 jack), the > installer fiddled around with his test gear on the phone line for a couple of > hours, but I can detect no difference in quality from my other phone line. It > is billed as a standard business phone line. I believe that every BOC has some type of "conditioned" central office loop for use with dial-up data. The additional charge may not be a tariffed item, but is instead a non-tariffed charge, which is sometimes referred to as a "special assembly charge". It sounds like the person to whom you spoke had little technical knowledge or experience with data communications - which unfortunately is par for the course. :-( > What does the switch, and the collection of resistors and capacitors inside an > RJ41 jack do? The resistors provide an attenuation for the transmitted signal from the modem, such that the signal arrives at the central office between -8 and -9 dBm. ---------------------------------------- >From postnews Sun May 10 16:51:48 1987 Subject: Re: Telephone answer detection Newsgroups: sci.electronics Distribution: usa Summary: Not that simple... References: <813@bgsuvax.UUCP> <837@killer.UUCP> In article <837@killer.UUCP>, royf@killer.UUCP (Roy Frederick) writes: > Detection of answer and hangup depends on the type of CO you are connected > to. Well-designed telephone apparatus should NEVER be dependent upon the characteristics of one particular type of central office switching apparatus. Those characteristics of any central office switching apparatus which might permit the detection of answer supervision by DC current sensing are unreliable, and are subject to change without notice by the operating telephone company. In North America, it is possible to design telephone station apparatus which will reliably work in any central office. Answer supervision, however, cannot be reliably detected though DC sensing means over a subscriber loop. Answer supervision must be detected by inference using call-progress tone detection, possibly in conjunction with a voice-operated switch circuit. > In some older type offices the line polarity is reversed while > you are connected to the called party. It goes back to normal when the > called party hangs up. There are in fact numerous variations and exceptions to this observation: 1. Some SxS offices have provide a polarity reversal for answer supervision only on calls made within the _same_ central office; non-toll calls made to other central offices may exhibit no such polarity reversal upon answer. 2. Some SxS offices have their "connectors" wired NOT to provide polarity reversal on calls within the same central office. 3. Some SxS offices provide a polarity reversal immediately upon the seizure of an interoffice toll trunk - regardless of whether the called party answers. This may also include calls to the Operator, directory assistance, etc. One reason for such polarity reversal is to facilitate "toll diversion" or "toll denial" for business lines and PBX trunks. Such polarity reversal may be restricted to "linefinder" groups dedicated just to business lines, or it may apply to all lines in the SxS office. The variations are numerous. > In newer offices, the line voltage drops to zero > momentarily when the party answers and again when they hang up. My CO > was a step-by-step with a common-control and used the polarity reversal > scheme. It was recently replaced by an electronic (type ?) office - it > now drops the voltage to zero very briefly. This is a dangerous assumption. Electromechanical switching apparatus (#1 crossbar, #5 crossbar, etc.) will exhibit a momentary switching open (lasting << 100 ms) as the marker switches the line from an originating register to an intraoffice trunk, or to an interoffice trunk. This time period is _extremely_ variable, and depends upon both the office traffic load and certain relay adjustment characteristics which are NOT subject to standardization. In analog ESS offices (#1 ESS, #2 ESS, etc.) there is also a switching open (lasting << 100 ms) as the line is switched between dial register, ringback tone trunk, and intraoffice trunk; or between dial register and interoffice trunk. This time period is also _extremely_ variable, and depends upon both the traffic load of the office and the operate-release time variations of bistable magnetic latching relays. In digital ESS offices (#5E ESS, DMS100, etc.) there is generally NO DC line current open until a call disconnects. > Busy (and for that matter all other call progress) tone are usually > detected by duty cycle. However, specific tone frequencies are used > for each signal. Teltone makes a nice chip that detects the tone > by frequency - I can't seem to find the reference to it (which contains > the actual tones and duty cycles) - but I'll post them later. Not all central offices use CCITT standard tones; this is especially true of SxS, Stromberg-Carson XY, AE/Leich, etc. electromechanical offices which are not equipped provide touch-tone (DTMF) service. CCITT standard (or "precise") tones primarily came into being with the implementation of DTMF service. Detection of call-progress tones MUST be made upon detected pulse shape (i.e., duty cycle and repitition rate) of any tone energy in the frequency range of 305 to 640 Hz; this covers "all bases". The _specific_ CCITT frequencies are never detected. <> 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 (05/13/87)
In a recent article VICTOR@YKTVMX ("Victor S. Miller") writes: > I've had a separate phone installed in my home for about five years to access > the computer at work via my IBM/PC. Ever since it was installed, I've had > bad problems with line noise. Even trying to use the phone for regular > voice is sometimes hard: I get periodic loud bursts of static (sometimes > more than a burst: the static can go on continuously for a few minutes). > Most days when I pick up the telephone I don't even get a dial tone (though > it varies). I've called the telephone repair service so many times, I don't > remember. The person taking the call has many times remarked about how bad > the static is. Nevertheless, they have never been able to fix it. One of > the problems is that things are often much worse when the weather is rainy > or damp (or a few days after a rain), and get better during dry spells, and > invariably, the repair person comes out on a nice sunny day, and says that > he can't hear anything. It doesn't matter what phone (or modem) I connect > to the line. I would think that the phone company would be tired of spending > money on sending out repair people, and would try to really fix it. The > other line in our house has been fine. One thing is that the bad line > has a phone number on a new (at least it was new when it was installed) > exchange. Could that have anything to do with it? It sounds like you have an intermittent problem with a wet cable splice or water getting into an outdoor junction box. Water can cause some really insidious cable problems which are usually difficult to locate. The problem can totally disappear during dry weather. I can believe that a telephone company repairperson can find no sign of trouble when finally being dispatched to your premises. The fact that your other telephone line is okay suggests to me that it leaves the central office in a different cable, before eventually being cross-connected to the same cable which feeds your block. The only way that the telephone company can deal with this problem is to catch it WHILE IT IS HAPPENING, and isolate the different cable sections between the central office and your house in an effort to localize the problem using leakage resistance measurements taken in each cable section. This could take a couple hours of effort, and requires two people: the person in the field and a craftsperson at a central office test position. It is often not easy to motivate the telephone company to expend the effort to solve this type of problem. Unfortunately, your best hope is that the wet splice will fail catastrophically - affecting many other subscribers, and therefore imposing some priority upon the matter. Here are my suggestions for dealing with this problem: 1. To whatever extent is possible or reasonable, inspect the telephone wiring at the point where it enters your house. Some older homes have outdoor protector boxes; if so, could this be filling with water when it rains? Try to spot the pole-mounted terminal box or cable-mounted "boot" where the drop wire to your house originates; are there open covers which could admit water when it rains? [I don't recommend climbing your utility pole for a closer look! :-)] If you see any of these conditions, take no action yourself, but DO inform a telephone company repairperson upon their next visit to your premises. I make these statements because, unfortunately, some telephone company personnel are lazy, and you have to "hold their hand" a bit if you want expedient service. 2. When the noise problem happens again, call repair service and tell them you want a repairperson dispatched NOW! Tell them this has been a chronic problem that has remained unsolved, and the only way to repair it is to find the trouble while it is happening. If you can't get satisfaction, demand to speak with a supervisor - that should get results. 3. If the problem goes away, and the telephone company claims to have fixed it, demand some details to satisfy yourself that the problem was in fact localized, and that a repair was in fact made. Unfortunately, lazy telephone company repairpersons sometimes report these problems repaired when it fact the problem spontaneously cleared without any actual repair effort. <> 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 (05/13/87)
In a recent article lav@mtsbb.UUCP (L.A.VALLONE) writes: > > Last week I stayed at the Days Inn in Alexandria, VA while on TDY. I > > was surprised to find that, plainly marked on the phone cradle, they > > charged 30 cents for 800 numbers as well as for local calls. Can they > > charge a "service fee" for toll-free calls? > > > > [The Sheraton Boston charges 60c for every 3 minutes on local calls, > > 950 calls, calls to the operator (except toll calls), calls to 911, > > and calls to 800 numbers. Apparently they can get away with it. --JSol] The "service fees" mentioned above are collected by the hotel from which the calls are made. These are usage charges for the telephone in the guest room, and have no bearing upon the actual cost of making the call. Since these charges constitute a "resale" of local telephone service, most if not all states through their respective Public Utilities Commissions regulate the maximum amount that a hotel can charge for guest telephone usage. Bear in mind that these hotel surcharges are not as outrageous as they may seem - for local calls, at least. In New York State, the measured business message rate for daytime calls through New York Telephone is around $ 0.10 per minute. In my opinion, charging for operator, 950 and 800 calls at the same rate as local station calls is unfair since it really costs the hotel NO money. However, the problem in many cases is that the PBX used by the hotel does not have the SMDR intelligence to differentiate between a free call, and a chargeable local station call. So, if in doubt, the hotel charges for ALL calls... > Does anyone know if 800 calls can be "charged" to an AT&T credit > card, thus eliminating the service charge? Since the "charges" for these toll-free calls are surcharges imposed by the hotel, AT&T has nothing to do with the matter. It is unlikely that AT&T will collect money for a hotel under these circumstances. I agree that say, $ 0.20 per minute is a ripoff for what should be a toll-free call, but the hotel seems to hold the cards in the matter as long as state Public Utilities Commissions permit such surcharges. Even if enough people complained to PUC's to reduced the surcharges permitted to hotels, the hotels would probably just turn around and compensate by raising their basic room rates. It's probably a no-win situation... <> 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 (05/23/87)
> In a recent article roger@SLEEPY.CS.CORNELL.EDU (Roger Hoover) writes: > A friend of mine has a cheapo phone that chirps every night at > 11:55pm. A call to New York Telephone about this got a response > claiming that NYT did no regular testing that would cause this. > A telephone on the same line with a mechanical ringer does not > make any noise. > > 1) What is causing this noise? I am willing to bet that the response from New York Telephone is incorrect. While the action of New York Telephone test apparatus may be precipitating the problem, the telephone company has no responsibility to take any corrective action; such a position may be difficult for the average customer to accept. Their "denial" of regular testing is either based upon specific ignorance of the person to whom you spoke, or is intentionally based upon paranoia of creating a whole new basis for customer complaints. The latter situation is probably more likely. It sounds to me like the telephone is poorly designed, and causes the "chirp" whenever telephone line battery voltage is removed and then reapplied to the telephone when it is on-hook. Most telephone company central offices have ALIT (Automatic Line Insulation Test) apparatus which is used to detect the presence of faulty outside plant cables. ALIT apparatus is programmed to test all regular telephone lines (loop-start only) for low leakage resistance from each conductor to ground. In operation, ALIT apparatus first determines if the line under test if busy; if it is, the line is not tested. If the line is idle, the ALIT apparatus connects to the tip and ring of the line, while DISCONNECTING the line from the off-hook detection battery source. The ALIT apparatus then makes a resistance measurement from tip-to-ground, and ring-to-ground; such measurements require no central office battery on the line. The ALIT apparatus then disconnects from the line and restores it to normal. The entire ALIT measurement time is between 1 and 2 seconds per subscriber line. Lines which fail the ALIT test (i.e., their leakage resistance to ground is BELOW a given threshhold), are listed on a printer or transmitted by other means to a telephone company test center. Most ALIT apparatus will also transmit an alarm to an attended test center if a significant number of lines fail the test. So the point is: the most likely explanation for the "chirp" is that ALIT momentarily disconnects the telephone from the central office battery, thereby creating a transient voltage which is falsely triggering the "chirp" circuit in the telephone. It is also possible that the test voltage from the ALIT apparatus itself is falsely triggering the "chirp" circuit. Since ALIT apparatus can only test lines that are idle, ALIT testing is always done between 2300 and 0700 hours. Since ALIT apparatus tests lines in numerical sequence, the test time of any given line will remain pretty much the same every night (unless the ALIT apparatus programming is changed). > 2) Is their an easy way to stop it? Buy a better quality telephone. :-) <> 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 (05/23/87)
In a recent article dbj@RICE.EDU (Dave Johnson) writes: > I need to wire a new phone line through a house for use with a modem. > Is there some kind of sheilded phone cable that I could use to help > reduce any noise in the connection? Anything else I should be aware > of when routing the wire such as not getting too close to electrical > wires? Thanks. I can think of no valid reason to use shielded telephone cable for wiring in a house. Most AC powerline noise is imposed upon telephone lines through induction rather than conduction or radiation, so any conventional shielded cable won't help this situation anyhow. Furthermore, the relative exposure of inside telephone wiring to AC powerlines is insignificant when compared to outside cable plant exposure to the electromagnetic fields of high-voltage AC transmission lines. Shielded cable is only useful for high-speed twisted-pair LAN devices or other high-speed data lines (56 kbits/sec or greater). I have only two suggestions for your wiring: 1. Try to find two-pair "inside station wire" which is _truly_ paired. Many two-pair station cables have four wires which are NOT paired, and therefore have some susceptibility to noise pickup and crosstalk. I wouldn't lose any sleep if you can't find such cable, however. 2. Try to keep at least a 2 inch separation between telephone cables and any powerline wiring. <> 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 (05/23/87)
> In a recent article dmt@ptsfa.UUCP (Dave Turner) writes: > > The following is from an editorial by Wayne Green in the June, 1987 issue > of 73 Amateur Radio magazine: > > The recent legislation making cellular phone calls illegal to listen in on > has provided a bonanza for both organized and disorganized crime. It's > difficult not to laugh over the situation the cellular industry has gotten > itself into in its blind pursuit of the fast buck. > > What's happened is a mass move into cellular by criminals. They buy a > cellular system, have an unscrupulous dealer alter the electronic serial > number (ESN) on the built-in programmable IC, which makes calls both > untraceable and free--a great combo. They tool around town, making calls > to Pakistan, Columbia, and their Caribbean drug warehouses at will. I have a few comments to make on this and some related topics which may be of interest to Net readers. My comments are based upon personal knowledge and experience as one who has provided some forensic science consulting services to certain law enforcement agencies for a number of years. It's sort of interesting to note that it was even easier to implement spoofing fraud in dial IMTS mobile telephone installations, but such fraud has been virtually unheard of. The reasons for this are: much fewer IMTS channels and much fewer IMTS customers than cellular make such fraud extremely conspicuous; most IMTS installations are combined with MTS installations and have a high probability of telephone company (or RCC) operator monitoring. My personal opinion is that cellular fraud has been encouraged due to "safety in numbers". :-) > Cellular has turned out to be great for coordinating every kind of criminal > activity. It's just what criminals have been needing for years-- a > dependable, free, untraceable, and safe communications system. With a > combination of pagers and cellular phones, crooks are making a shambles > of the cellular system--all protected by Congress. > > If you wanted to deal in drugs, how better to get orders from your > customers than by giving them your cellular phone number? There's no way > to tap a telephone that can be anywhere in a big city, operating through > different cells as it moves around. And with an altered ESN it's all free! Progress in telecommunications has unquestionably been of benefit to criminal activity. Probably the single greatest benefit has been the introduction of call forwarding. This service has been of such great benefit to the conduct of unlawful gambling, narcotics and prostitution operations that for many years I have jokingly referred to it as: "1A Criminal Facilitation Service"; AT&T and BOC people may appreciate the satire in this remark. As an example, an unlawful gambling operation could change location every day or so, with the telephone number for bettors being the same. This situation also neatly defeats any court-authorized eavesdropping warrant since there would never be conversations on the telephone pair that was the subject of such a wiretap; a forwarded call never takes place on the physical line whose number was dialed. In earlier No. 1 and No 1A ESS installations there was no rapid method to determine to what number a given line had its calls forwarded; such determination could only be made by an experienced switchman using the ESS maintenance tty. This rather frustrated law enforcement agencies in their investigation of unlawful gambling and narcotics activity. Furthermore, I know of some instances where telephone company personnel flatly denied to law enforcement investigators that they could determine the forwarded telephone number; this was, of course, a false statement, but was made in a misguided effort to keep the telephone company "uninvolved". As an interesting aside, prior to the advent of ESS and call forwarding, some larger unlawful gambling operations used an electronic device called a "cheese box" that effected a rudimentary kind of call forwarding in a manner similar to a loop-around test line. Two telephone lines would be ordered for say, an unoccupied office or apartment, and each line would connect to the "cheese box". The actual location of the gambling operation would call the first line, and remain on the line and wait for calls; the "customers" would call the second line, with the result that it would auto-answer and be connected to the first line. Telephone company loop-around test lines were used for the conduct of unlawful narcotics dealing during the 1970's, but this practice has generally disappeared as telephone companies: (1) installed 60A control units or equivalent devices that dropped loop-around connections upon the detection of speech energy (legitimate use of loop-around test lines is for single frequency transmission measurements only); and (2) went ESS and therefore had "call trace" capability that would automatically determine the origin of calls to loop-around and other test lines. After call forwarding, the next most useful communications adjunct to criminal activity is the voice radio pager. It is an unfortunate fact of life that no self-respecting prostitute or "street dealer" of narcotics would be caught without their voice pager. Voice pagers represent an ideal, inexpensive method of arranging clandestine meetings. A typical voice pager scenario: customer calls narcotics dealer's pager from a coin telephone, giving coin telephone number; narcotics dealer finds coin telephone to call coin telephone where customer is waiting to arrange for a meeting. What could be simpler and more untraceable? In my travels, I have known of only two instances where criminals used any speech privacy devices (speech scramblers) to defeat eavesdropping (lawful of otherwise); however, I suspect that a new generation of low-cost digital speech privacy devices will result in more of these devices being used by criminals. The units that I have seen used were all based upon analog "speech inversion" techniques; these devices are easy to defeat, whereas the digital devices are virtually impossible to compromise by other than NSA. One of the most novel (at the time) applications of communications technology by criminals that I have personally seen was the use of telecopiers by a large unlawful gambling operation about 11 years ago. While the law enforcement agencies involved had obtained eavesdropping warrants to install wiretaps on some of the telephone lines involved, they were totally baffled by the strange sounds heard during some intercepted calls. I was called in to solve the mystery, and some listening told me that this was an FSK facsimile machine running in 6-minute mode. So we borrowed a telecopier to decode the tapes; this was not as easy as first anticipated. I finally had to modify the telecopier to start in receive mode without receiving a ringing signal (which was not possible from an after-the-fact tape recording). We got some pretty damning evidence, much to the consternation of the criminals (who suspected a wiretap, but felt that the facsimile machine was "secure"). While telecopiers are rather common today, such was not the case 11 years ago. I suspect that as telecopiers decrease in price, they too will be more commonly used by criminals. While Group I and Group II facsimile machines are fairly easy to monitor, the more common Group III (sub-minute) machines are much more complex since they are digital and require faking a handshake protocol by any receiving machine used as a monitor. > If it weren't against the law to listen to cellular channels, I'd suggest we > hams help the law by listening for suspicious cellular calls and recording > them. Say, how'd you like to get the goods on some serious crooks and find > (a) the evidence is inadmissible because it was illegally attained and (b) > yourself on trial for making the recordings. So join me in a big laugh, okay? I know of law enforcement agencies that have in the past used scanners to listen to paging service channels and IMTS mobile telephone channels, and have obtained useful intelligence information. None of the information so derived was used in court per se, but it may have contributed to the "probable cause" for looking in a certain _public_ place at a certain time. When any investigator was pressed in court for the "basis of probable cause", the information was attributed to an "anonymous informant" - a VERY common source of law enforcement information. Under the circumstances, I see nothing wrong with this - but I am certain that a number of people will disagree with me. For example, an experienced investigator can readily detect a drug deal going on via certain types of pager messages. Now, if a police cruiser just happened to be going by the aforesaid location, and decided it was time for a routine traffic check... :-) [Flames about prosecuting people for alleged "victimless" crimes such as gambling, narcotics and prostitution should be directed to /dev/null] <> 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?"
pozar@hoptoad.UUCP (05/26/87)
In article <8705230318.AA03545@seismo.CSS.GOV> kitty!larry@SEISMO.CSS.GOV writes: >In a recent article dbj@RICE.EDU (Dave Johnson) writes: >> I need to wire a new phone line through a house for use with a modem. >> Is there some kind of sheilded phone cable that I could use to help >> reduce any noise in the connection? Anything else I should be aware >> of when routing the wire such as not getting too close to electrical >> wires? Thanks. > > I can think of no valid reason to use shielded telephone cable I can give you one reason: RFI or Radio Frequency Interference. I spec'ed a Northern Telecom SL-1 (s series) for our AM station in San Jose. I knew at that time there was some pretty nasty RF levels in the building and cofermed them with a RF field strength meter. 200volts per meter! The building contains a 50Kw transmitter and sits in the main lobe of the direc- tional. When we spec'ed the SL-1, I told Pac Tel (the folks we were purchasing the switch from) that they would be encountering some high RF and shielded, twisted pair would be advisable when installing the sets. They said, "No problem", and instaled unshielded, twisted pair. Boy did they lose money on our purchase! They had to not only reinstall shielded, twisted pair, but drop .01uf caps on all the lines and ferrite beads! Now I relize that most houseing will not be right next to a 50,000 watt AM radio station, but if you are one of the small unfortunate RFI can be handled with shielded wire and mabey a couple of .01uf caps. -- Tim Pozar UUCP pozar@hoptoad.UUCP Fido 125/406 USNail KLOK-FM 77 Maiden Lane San Francisco CA 94108
larry@cs.buffalo.edu (10/09/88)
In article <telecom-v08i0147m08@vector.UUCP> kaufman@polya.stanford.edu (Marc T. Kaufman) writes: > >I'm looking for a relay to place in series with a telephone which will > >open (or close) when the set is offhook. The closest I've come is with > >a 200 ohm 4.5 mA relay. It didn't affect the phone operation too much, > >but wouldn't quite pull in. If I pressed the armature in, it would > >latch. Close, but no cigar. > > You want to use a voltage comparator IC to measure the voltage between the > wires (through a full wave bridge rectifier, so you don't have to care which > way you hook it up). Open circuit (on-hook) voltage is about 48, off-hook > voltage is about 1-2 volts. I am not sure what "hold" voltage is, but it is > higher than 2 volts. Simpler, for a single phone, is to see if the phone has > a spare set of contacts on the hook switch (many do), and use them. A few words of advice on the design and construction of such a circuit: 1. In general, it is good practice to isolate any voltage comparator circuit by using a 100,000 ohm resistor in series with the tip lead and the ring lead (i.e., two resistors, 200 K effective impedance across telephone line). This means that the voltage comparator circuit needs to have a high input impedance to function with such a high input series resistance. This is really not a problem for a well-designed circuit. The input circuit to the comparator or op amp (i.e, following the two 100 K resistors) MUST be protected against voltage transients caused by ringing voltage, dialing pulses, etc. Such protection can readily be accomplished with a pair of back-to-back zener diodes. In addition, a parallel capacitor should also absorb some transients and prevent spurious signals. While the capacitor will result in a time constant when used in conjunction with the 100 K series resistors, this is desirable - a time constant between 300 and 600 ms should be fine since the output of the voltage comparator does NOT want to follow rotary dial pulsing in a status indicator application. 2. The use of the 100 K series resistors protects both your equipment and the telephone network. Under these circumstances, a short between the comparator or op amp input and Vcc or ground will cause neither harm nor appreciable degradation of voice signal. 3. The statement above that "off-hook voltage is about 1-2 volts" is not correct. Off-hook DC voltage typically ranges between 6 and 25 volts, depending upon the resistance of your CO loop and the internal resistance of your telephone set. From a realistic standpoint, a threshhold of 35 to 40 volts (some hysterisis is desirable to prevent transients from causing spurious signals) is reasonable for the design of a voltage comparator circuit. 4. A well-designed status indicator circuit is polarity insensitive. You can do this with a full-wave bridge rectifier prior to the voltage comparator, or with multiple comparators (may be more convenient when using quad comparators or op amps). 5. In general, DC holding resistors range between 200 and 400 ohms so that "hold" voltages approximate those of off-hook voltages. A realistic range is 5 to 25 volts. 6. Higher off-hook voltages will usually be present if you are using the above status circuit on a PABX extension. In general, -48 volt battery and ground is still fed through a total of 400 ohms (or electronically current-limited to an equivalent value), but there is very little loop resistance. So, a 500-type telephone set as a PABX extension will generally show an off-hook voltage between 20 and 25 volts. <> 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?"
larry@cs.buffalo.edu (10/09/88)
In article <telecom-v08i0150m10@vector.UUCP> tedk@ihuxv.ATT.COM (Kekatos) writes: > | I'm looking for a relay to place in series with a telephone which will > | open (or close) when the set is offhook. The closest I've come is with > | a 200 ohm 4.5 mA relay. It didn't affect the phone operation too much, > | but wouldn't quite pull in. If I pressed the armature in, it would > | latch. Close, but no cigar. > | So, what type of relay should I be looking for (impedance/current). Is > | such a thing commonly available? Will this scheme work? Does ringing > | current cause any problems? > > Sorry, This can not be done with a ONLY a relay. You just can not > draw enough current from the phone line. This is incorrect. Since the beginning of time :-), relays have been available which operate on series telephone loop current. Typical off-hook loop current ranges from a low of 0.020 A (long CO loop) to 0.1 A (sitting next to a PABX). In the "traditional" key telephone system world, the 6-type KTU (Key Telephone Unit) has been around for at least 50 years. This device consists of a single WECO B-type relay wired to screw terminals on a small mounting bracket. I don't have the exact relay specs handy, but the relay picks up at somewhat less than 0.010 A and has an internal resistance of around 20 ohms. The relay will withstand at least 0.2 A of overcurrent with no damage. There are various types of non-polar relays which exhibit this degree of sensitivity. In the past 25 years, reed relays have been particularly popular for loop current detection, since a reed relay is sealed and requires no adjustment. With respect to the article by the original poster, a relay with a series resistance of 200 ohms introduces too much series resistance for a "good design". A series resistance of less than 75 ohms should be used. A common circuit design practice is to place a non-polarized capacitor (0.5 to 2.0 uF) across the relay winding to minimize voice frequency attenuation. While the 200 ohm relay used by the original poster has an undesirable high resistance, it SHOULD have still worked in a normal telephone loop. If it did not work as described, that it was either maladjusted, damaged or did not in fact have a sensitivity of 4.5 mA. Bear in mind that I am not advocating the use of relays in place of solid-state device (like the opto-isolator). I am merely pointing out that relays will in fact work, and for some applications, a scrounged up 6C KTU is still the simplest solution. <> 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?"
larry@cs.buffalo.edu (10/09/88)
In article <telecom-v08i0154m03@vector.UUCP> MCHARRY%BNR.CA@MITVMA.MIT.EDU (J.) writes: > Some years ago I saw a nifty way of putting a 'busy light' > on a phone. Normal phone systems have the tip wire grounded > and the ring hooked to -48v. (Some systems fail to provide a > ground reference.) ALL telephone systems are designed to provide a "ground reference", and for certain, ALL central offices would be installed in this manner. The only exception to the above is a PABX which was incorrectly installed (it certainly wasn't designed that way!) without a ground connection. > The trick is that both -48 and ground are > applied through about 200 ohms. When a phone on the loop is > off hook, tip and ring are nearly shorted together, and appear > at about -25v to ground. An led hooked through a resistor to > the tip side will come on if anyone is off hook. Of course, > there is a catch or two: 1) You have to make sure the ground > wire is connected and not just tip and ring. You may have to > hook it up at the building entrance block. 2) This will > likely introduce a large ground loop and a lot of hum. A loud hum, eh? What we have here is, ahem, a classic example of what is properly called "longitudinal imbalance". You won't get FCC Part 68 certification with that design! :-) > I haven't > tried this, but old ringers are usually rigged with two windings > having a blocking cap between them. Going from the tip side > winding to ground might stifle the hum. Alternatively, a good > sized choke in series with the led ought to kill it also. The > resistor is 25k / (number of mils to light the led). I would suggest not trying ANY variation of the above scheme. There is NO WAY to design an acceptable circuit based upon the above technique. There is never any justification to sense line status (i.e., on-hook, off-hook) by means of any external ground reference, regardless of how high a bridging impedance is placed across tip and ring. The only exception to this statement involves ground-start PABX trunks or coin telephone lines - which is not exactly what we are talking about. There are numerous ways to sense line status by means of ISOLATED sensing of series loop current, or by high-impedance (> 100,000 ohms) briding across tip and ring to sense loop voltage. No ground reference is needed in either of these techniques. <> 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?"
larry@cs.buffalo.edu (10/09/88)
In article <telecom-v08i0148m08@vector.UUCP> mgrant@cos.com (Michael Grant) writes: > A long while ago someone posted a question about how to build a simple > circuit which would light a LED (or a simple lamp) when an extension > was lifted elsewhere in the house. The requirements are: > > - The LED lights when another extension is lifted, showing that it > is in use. > - The LED must be powered off the phone line. > - No extra wires must be run to the telephone. > - The circuit should be reasonable small so that it can fit inside a > desktop style phone. > > No one was able to come up with a simple schematic to do this that > worked. The upshot was that one could buy such a device for about $30 > off the shelf. Having let some time pass, anyone want to give a stab > at this? Bear in mind, that we appear to be discussing a means which bridges across tip and ring, and which operates by sensing loop voltage, and NOT loop current in series with an off-hook telephone set. There is NO WAY to properly design a circuit as you describe which will not run the risk of interfering with the proper operation of the telephone line. Proper telephone circuit design practice dictates that a bridging impedance across a telephone loop must never be less than 100,000 ohms. This means that the MOST current that one can draw is 50/100000 = 0.0005 A. One can't light an LED on 1/2 mA! The situation is really worse than the above, since we want to light the LED in an off-hook condition, where the loop voltage at the telephone set is between 6 and 25 volts. Even taking the "best" value of 25 volts, 25/100000 = 0.00025 A, which means that only 1/4 mA could be available off-hook to light an LED! Under many conditions, one can fudge the 100,000 ohms bridging impedance to 50,000 ohms without loop interference. However, for the above purposes, there is still an insufficient amount of current which can power the LED (1/2 mA off-hook at best). Trying to bridge a lower resistance across the loop to create more energy to light the LED is an invitation to trouble in the form of: (1) interferring with rotary dial pulsing by causing pulse distortion; (2) false tripping of incoming ringing signals; and (3) generation of trouble reports by automated central office equipment (both ALITS and ESS test procedures). I'm afraid that we have to hang up on this idea. Voltage sensing across tip and ring is okay - but the indicator power is going to have to come from a source other than the telephone line. <> 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?"
larry@cs.buffalo.edu (10/10/88)
In article <telecom-v08i0151m03@vector.UUCP> ssc-vax!clark (Roger Clark Swann) writes: > I just got through making a phone call from my office here in > Seattle to our plant in Huntsville, AL. The hardware at each end > should be a #5ESS (I am told). The routing of the call should > normally be over private, leased circuits and should NOT be going > onto the public network. It turned out that the phone I was trying > to reach in Huntsville was busy for several tries. Each time, an > audio circuit was opened and the busy signal was generated at the > far end. Now with that background, here is the my question: > Why wasn't the busy signal generated by the PBX equipment at my end? It sounds like you have some variant of Centrex service, with some type of tie line network. Whether the tie lines are "conventional", furnished by CCSA (Common Control Switching Arrangement), or part of an ETN (Electronic Tandem Network), the switching behavior using today's technology is all the same: the call is still physically completed to the far end switch. The far end switch provides the supervisory tone indications of busy, ringing or recorded intercept, and connects the call if possible. Typical busy signal "holding time" is so short (a few seconds), that there is no significant advantage in immediately dumping a tie line call and furnishing busy tone from a trunk within the near end switch. This situation may change in the future as switching systems become more sophisticated and exchange high-speed digital information prior to setting up a talk circuit - would would occur ONLY if voice connection were in fact needed. > I thought that the system did some talking over a data link before > opening the audio path anyway. If you are referring to CCIS, then the information pertains only to the dialed digits and originate/answer supervision. As far as existing CO and PABX equipment is concerned, a no-answer (i.e., ringing at the far end) and a busy condition is the same. The "audio path" is opened with virtually no delay as you complete dialing of the last digit of the access code(s)+telephone number. The far end switch is responsible for returning all supervisory tones, except when no tie trunks are available from your site or an intermediate switching center. > If so, the 'busy' should be signaled > over the data link and the local equipment would take care of it This may become commonplace in the future, but I would be extremely surprised if your organization had equipment which operated in this manner. I know that work has been done by AT&T, Northern Telcom, and Rolm with respect to more sophisticaled digital signaling protocols over a true digital data link, but the only implementations that I have seen pertain to CAS (Centralized Attendant Service). <> 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?"
chip@vector.UUCP (Chip Rosenthal) (11/02/88)
In article <telecom-v08i0161m05@vector.UUCP> wendyt@pyrps5.pyramid.com (Wendy Thrash) writes: > > I'm the formerly happy owner of a Panasonic answering machine similar to one > described in a recent article here. A week ago I moved to San Francisco. > My phone line is the third one in the apartment, and the wires were apparently > run by a friend of my roommates rather than by Pac Bell. My phone works OK > in the new apartment, but my answering machine will not work; it answers the > phone, jiggles its tapes a couple of times, and hangs up. > > I think the machine believes that another extension has been taken off hook, > and courteously relinquishes the line. This would be a feature if, in fact, > another extension had been taken off hook, but there is no other extension > on the line. > > My answering machine works fine on my roommates' lines. Their answering > machines work on my line. I doubt that improper wiring is the problem; otherwise you would be having other noticeable problems like hum or crosstalk. Based upon the manner in which you have swapped machines and lines, and your results, my guess is that YOUR line may be served through some type of subscriber line carrier or concentrator device. While "normal" telephones will work on subscriber line carrier devices, the tip and ring voltage is often MUCH less than that supplied through a "normal" line. In the case of analog FDM systems like the Continental AML variety, on-hook voltage is ONLY 6 VOLTS! The older WECO 1-type concentrator used 24 volts, rather than the usual 48. So, your telephone answering machine may not get sufficient off-hook loop current following ring-trip and answer, and therefore think that an extension has been picked up. Subscriber line carrier or concentrator devices are used to effect "pair gain" in rapidly growing areas where there are insufficient cable pairs to service the subscribers; i.e., the apparatus multiplexes through analog FDM or digital PCM additional subscriber lines on one physical pair. To find out for certain about the status of your telephone line, measure the on-hook voltage with a digital voltmeter. If it is less than 48 volts, then you have just confirmed the problem. Newer WECO subscriber line concentrator systems (like the SLC-96) present 48 volts, and should not cause a problem. It sounds like you are probably served by an older device of some sort. In general, you have no "right" by virtue of telephone company tariffs to insist that your telephone line be a "physical" pair rather than multiplexed. However, you can politely ask. If all else fails, you can always drive the telephone company repair service nuts by repeated calls complaining about line noise; multiplexed circuits are almost always noisier than physical circuits, and they may change your pair to a physical one just to shut you up. :-) <> 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?"
jbh@umix.cc.umich.edu (James Harvey) (11/03/88)
{{{ Quoted text edited *severly* to pass inews. -chip }}}
In article <telecom-v08i0157m05@vector.UUCP>, kitty!larry@cs.buffalo.edu writes:
> In article <telecom-v08i0154m03@vector.UUCP> MCHARRY%BNR.CA@MITVMA.MIT.EDU (J.)
> writes:
>
>> Some years ago I saw a nifty way of putting a 'busy light' {{{...}}}
>> (Some systems fail to provide a ground reference.)
> ALL telephone systems are designed to provide a "ground reference",
> {{{...}}}
The number Five ESS (AT&T) does NOT provide a ground reference
while in the talking condition. Even for ground start lines!
>> {{{...}}}
> A loud hum, eh? What we have here is, ahem, a classic example
> of what is properly called "longitudinal imbalance". You won't get
> FCC Part 68 certification with that design! :-)
Very true, Part 68 requires 60 db of balance for certification.
> I would suggest not trying ANY variation of the above scheme. {{{...}}}
> There are numerous ways to sense line status by means of
> ISOLATED sensing of series loop current, or by high-impedance (> 100,000
> ohms) briding across tip and ring to sense loop voltage. No ground
> reference is needed in either of these techniques.
I believe the only solution is to buy a ground start line from
your local telco. Might have to rig a special phone up to draw
dial tone properly. This is the only way to ensure a ground on
your line when in use. On the 5ESS, you have to sense the ground
and remember it because it goes away as soon as the switch
converts to the "Talking" state.
> <> 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?"
--
Jim Harvey | "Ask not for whom the bell
Michigan Bell Telephone | tolls and you will only pay
29777 Telegraph | Station-to-Station rates."
Southfield, Mich. 48034 |
ulysses!gamma!mibte!jbhjbh@mibte.UUCP (James Harvey) (11/03/88)
{{{ For some reason, message 6 is a duplicate of message 4, and }}}
{{{ therefore I have omitted it here. -chip }}}