larry@SEISMO.CSS.GOV@kitty.UUCP (12/28/86)
In article <2263@well.UUCP>, rab@well.UUCP (Bob Bickford) writes: > > Dialing a three-digit access code which immediately provides an > > announcement over the telephone circuit. This unrestricted > > implementation has generally been considered a "security" problem > > (use your imagination) by telephone company management; I am > > somewhat surprised to see people posting articles reporting the > > implementation of unrestricted ANAC. > > Why? I'm afraid my imagination does not present me with any > compelling reason to belive this a 'security risk'. Certainly it > is of little or no use to a telco cracker. Well, I guess I have to spell it out... The availability of ANAC at any outside plant location (like cross-connect terminal) is of significant value to anyone bent upon unlawful wiretapping. Telephone company security personnel are always concerned about unauthorized persons obtaining any information with respect to subscriber line pair identity and circuit routing. In fact, in New York State it is a specific criminal offense (Penal Law 250.30) for an "unauthorized" person to obtain "information concerning identification or location of any wires, cables, lines, terminals or other apparatus used in furnishing telephone or telegraph service". Since people are reporting unrestricted ANAC in California, perhaps life there is more permissive. :-) > > You are referring to milliwatt test lines which provide a 1,000 Hz > > signal at 0 dBm (1 mw) into a 900 ohm termination. Some milliwatt test > > lines provide a continuous tone; others have 9 seconds of tone followed by > > 1 second of silence (with or without answer supervision). > > Ours are 8 seconds and 2 seconds; the tone by the way is 1004 Hz > and NOT 1000 Hz. Traditionally, the milliwatt reference frequency was 1,000 Hz, and still is 1,000 Hz in many central offices (especially those that are still electromechanical). Interestingly enough, the milliwatt reference frequency has been changed in some areas to 1,004 Hz because of small measurement errors which occur when measuring through PCM (i.e., digital) CO's or transmission (T-carrier) facilities. The reason is that 1,000 Hz is an even divisor of the 8,000 Hz PCM sampling rate, and any frequency within say 1 Hz of 1,000 Hz exhibits erratic results (to a minor degree, however) during measurement. > > A word of caution concerning the use of milliwatt test lines: if > > you don't know what you are doing and don't have the proper test equipment, > > you will be fooling yourself with incorrect measurements. > > Quite true. We wasted several weeks working on the audio portion of > our video conferencing system when I was at Vitalink Communications. > Finally we purchased a Halcyon tester (don't recall model #) and > stopped listening to the linemen who kept insisting that the line was > a 600 ohm line. There is a good moral to be learned here: Don't ever accept as gospel any transmission-related information given by telephone company craftspersons (also salespersons!) - either get it from someone that you _know_ is an engineer, or measure it yourself. Not that I have anything against non-engineers, but many telephone company craftspersons just follow orders and directions, with little or no understanding beyond that. For example, even a craftsperson using a TTS to make transmission measurements will have _explicit_ instructions how to set the controls on his TTS and then get a meter reading - but more often than not, will have no idea why the TTS is operated as he has it configured. > > Almost all CO's provide three "quiet lines" for noise measurement > > purposes and repeater test purposes: (1) a balanced termination; (2) an > > open-circuit termination; and (3) a short-circuit termination. The latter > > two lines are primarily used to test negative impedance repeaters for > > noise and "singing". > > That's strange, we seem to only have one variety of quiet line around > here, and that's the terminated one. You might not know the numbers for the others. Actually, there may be TWO lines with balanced terminations (in addition to one for open-circuit and one for short-circuit). Many CO's use a CLA (combined loop-around) for a milliwatt test line. The CLA uses two sequential numbers (common example 9911 and 9912 applied to New York Telephone) which work as follows: 1. Dialing _only_ the 9911 number gives you milliwatt tone. 2. Dialing _only_ the 9912 number gives you a balanced termination. 3. Dialing _both_ 9911 and 9912 gives you a bridged connection between the two lines whose insertion loss is the typical CO switching loss (usually well under 1.0 dB). This is referred to as "loop-around" mode, and is used for remote transmission measurements to and from a CO; its primary purpose is to test interoffice trunks, and it has no usefulness for subscriber loop meqsurements. Many newer CO's have a speech energy detector on the CLA which drops the connection if _other_ than SF tones are sent in loop-around mode; this has been implemented to stop "unauthorized" people from using the CLA for talking. So, in addition to the balanced termination available through the CLA, most CO's still have a short-circuit termination (typical 9954 suffix for New York Telephone), an open-cicruit termination (typical 9955) and another balanced termination (typical 9956). Note that in addition to a milliwatt line being available through the CLA (9911 as above), there is usually a dedicated milliwatt line (typical number is 9910). There is generally an important distinction between this apparent duplication of test lines: the CLA is used primarily for interoffice trunk measurements, so its impedance is 600 ohms - whereas all of the other lines have 900 ohm impedance. <> Larry Lippman @ Recognition Research Corp., Clarence, New York <> UUCP: {allegra|bbncca|decvax|nike|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?"
ET@DEEP-THOUGHT.MIT.EDU.UUCP (01/02/87)
Noticing all the questions about ring-backs, I thought I'd send this one
in...it's for finding out what number you're calling from, though.
In the Boston area (at least), the number is 1-200-555-1212. I assume
the last four digits may be anything, but I haven't tried it out, yet. I
suggest you not use it too much, though, lest the phone company catch on and
change it.
Does anyone know what the number for this "service" is out in Southern
California (Los Angeles area, specifically)? And also the ring-back number out
there?
Quick responses would be much appreciated, for I leave for home (for
good...graduating) on 17 Jan 87...thanxz!!!
Vic Christensen
ET@MIT-DEEP-THOUGHT (or ET@EE)
ET%MIT-DEEP-THOUGHT@MIT-MC (or ET%EE@MC)
2109 Amelia Avenue
San Pedro, CA 90731
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