nourse@nac.dec.com.UUCP (05/06/87)
> Path: decwrl!decvax!ucbvax!kitty.UUCP!larry > Subject: Telephone line quality > Posted: 19 Apr 87 05:35:00 GMT > ... 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. > ... 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. > 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. > ...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. > This is NOT a "plug" for AT&T; it's just a simple fact of life since > AT&T still runs all the major toll switching centers in the U.S.) That may be why we still don't have `equal access'. (New England Telephone says there are `no plans' to implement it, or even touch-tone, in our town). To use an alternate carrier, we have to dial: 1 <CLACK!!><HISSSSSSSSSS>-950-0xxx <wait up to 15 seconds> [access code][number] When I've used Sprint from a place with decent equal-access, the line quality was better than 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. What does the switch, and the collection of resistors and capacitors inside an RJ41 jack do?
larry@kitty.UUCP (Larry Lippman) (05/09/87)
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. <> 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?"