larry@uunet.uu.net (Larry Lippman) (09/06/89)
> In article <telecom-v09i0343m02@vector.dallas.tx.us> msa@rwing.uucp (Mark Anacker) writes: > Their phone service is party line, with 3 or 4 others on > the line. Instead of the old system of "1 long, 2 short" rings or whatever, > telco sends the rings signal at different frequencies for each party. Thus > my friends' ring is 50Hz, instead of the usual 20Hz. They then had to buy > a small box that goes inline with their incoming line and beeps when a > ring signal of the appropriate frequency comes along. A side effect of this > is that the ring signal is not passed through the box at all, making it > kind of hard to hook up an answering machine or modem (or anything). I think the *intention* was to make it "kind of hard"; read on... > Also, since the only audible indicator is in the filter box, you can't hear > the phone ring outside that room. > What I had in mind was to modify one of these filter boxes so that instead > of beeping on a 50Hz ring, it would close a relay and bridge the house > side of the line onto the incoming side. This would then allow the ring > signal to get to the rest of the house. We've verified that their phones > and stuff will recognize a 50Hz ring (also all other rings), so they > should work. I'd like to know if anybody out there has done anything > like this already. Most telephone companies frown upon the use of ANY telephone accessory on multi-party lines. In addition, FCC Part 68 certifications generally do NOT apply to party line use. There are many reasons for such a restriction, not the least of which is that if you cause trouble on your line, you cause trouble on everyone else's line. Since people depend upon a telephone in a rural area to summon emergency assistance, there is much more than "inconvenience" involved. Most states have laws which REQUIRE that use of a party line be IMMEDIATELY relinquished if an emergency is announced. The use of a modem or fax machine obviously makes it difficult for the subscriber using the line at a given moment to hear such a request to free the line for an emergency call. However, from a practical standpoint, it is most likely that a modem or fax call would lose carrier or sync and disconnect if someone picked up on the line and began talking. However, I would not like to test this issue in any court. Other reasons for controlling station apparatus on a party line is that such apparatus may interfere with billing if message rate and/or ANI toll service is provided. Two-party lines are commonly arranged for "tip party identification" (a balanced ground using the ringer windings or a terminal on the network) to facilitate message rate and ANI. Four-party lines generally have no message rate service, and usually rely upon ONI for toll calls. And if you are in GTE territory, you may have a "SATT" dial (don't ask...) instead of the more common tip party identification. As far as answering machines are concerned, they may also be prohibited. I have never seen any answering machine which could handle any type of selective ringing except for two-party grounded ringing. And those were OLD answering machines from the 1970's in which one side of the ring detection circuit was brought out on the yellow wire. All newer answering machines seem to rely solely upon bridged ringing. Getting back to your question, regulatory issues notwithstanding, to PROPERLY build what you describe may not be trivial. From your description, this "black box" appears to block any ringing signal - which appears to complicate the situation. Under these circumstances, while "decimonic" (the use of four frequencies, 20 Hz, 30 Hz, 40 Hz and 50 Hz) frequency-selective ringing may be used, it may in fact be _grounded_ ringing, with or without superimposed DC. Should this be grounded ringing, then there is NO simple way to create a bridged ringing signal for use with a conventional modem or telephone answering machine. My best advice is to leave this situation alone and advise your friends to see if their telephone company will furnish a single-party line. Then there won't be a problem, and there won't be any risk of interference to the other subscribers on the party line. <> Larry Lippman @ Recognition Research Corp. - Uniquex Corp. - Viatran Corp. <> UUCP {allegra|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> TEL 716/688-1231 | 716/773-1700 {hplabs|utzoo|uunet}!/ \uniquex!larry <> FAX 716/741-9635 | 716/773-2488 "Have you hugged your cat today?"
roy%phri@uunet.uu.net (Roy Smith) (09/18/89)
kitty!larry@uunet.uu.net (Larry Lippman) writes: > However, from a practical standpoint, it is most likely that a modem or > fax call would lose carrier or sync and disconnect if someone picked up > on the line and began talking. I have heard stories of people with Telebit TrailBlazers who have picked up a phone on the same line as the modem, while it was on line. They heard a lot of screaching, but the modem didn't miss a beat. For those not familiar with TrailBlazers, they talk some kind of packetized, error-corrected, protocol between themselves, and have the ability to adapt to amazingly bad phone lines. I wouldn't be surprised if some of the new MNP level-whatever or V.32 modems would be similarly resistant to loosing a connection just because sombody picked up a phone on the line. Roy Smith, Public Health Research Institute 455 First Avenue, New York, NY 10016 {att,philabs,cmcl2,rutgers,hombre}!phri!roy -or- roy@alanine.phri.nyu.edu "The connector is the network"