larry@uunet.uu.net> (04/06/90)
In article <5724@accuvax.nwu.edu> MHS108@psuvm.psu.edu (Mark Solsman) writes: > I agree with you that that phone could not ring because of physical > switching in the phone, but what about other phones on the same > extension? If you send the correct signal (70volts AC??) through the > lines, wont all the other phones ring that were not previously > off-hook? Or would this cause considerable damage to the origional > phone that was off-hook? > [Moderator's Note: How about a technical reply on this from the > experts? PT] You rang? :-) In general, the ringing supply from an SxS or XY connector, or from an intraoffice or interoffice trunk in any other type of CO, will not operate bridged ringers on a station line where one station is off-hook. There are three reasons for this: 1. First and foremost, if a station is off-hook, the line is already marked busy and an incoming call will not be permitted, although in a contention situation usually called "glare" the next two reasons come into play. 2. The shunt resistance of the off-hook station will *immediately* operate the ring-trip relay or ring current sensing circuit, therefore removing the ringing supply connection. 3. The current limiting provided by the CO apparatus does not allow enough voltage to develop across the shunt resistance of an off-hook station set to operate any bridged ringers. However, there are two circumstances in which bridged ringers may operate in the presence of an off-hook station: 1. A service bureau test position provides a ringing supply under manual control (without any ring-trip relay) having a higher current-limited value than found in normal CO switching apparatus. Therefore, if a craftsperson "cords" a subscriber line to a test position and lays on their manual ringing key, a bridged ringer *may* operate in the presence of an off-hook station, if the CO loop resistance is not too great. 2. Some DSA and toll trunks to some CO's have a manual ringing extender relay located in the remote CO recording-completing trunk circuit which can be operated by the DSA or toll board "ring forward", "ring reverse" or "re-ring" keys. I remember a common recording-completing trunk circuit (SD-31180) from my SxS days which had a ring control relay operated by the DSA or toll position which connected continuous ringing supply directly to the subscriber line through a pretty healthy resistance lamp. If any circuit could provide enough ringing current to operate a bridged ringer in the presence of an off-hook station, this one could! In article <5813@accuvax.nwu.edu> bruner@uicsrd.csrd.uiuc.edu (John Bruner) writes: > I have read the explanations of why it is impossible to ring a busy > telephone with some interest, because I remember it happening in my > parents' house a long time ago. We had a party line, and the other > party had left their telephone off-hook. My parents called Indiana > Bell from a neighbor's telephone. There was a very strange ring in > the house (a set of very short rings), and when I lifted the receiver > of one telephone, the other one continued to ring. Party line ringing is often implemented using various combinations of ringing in the presence of DC bias from GROUND to one side of the telephone line. While a call dialed through a multi-party connector would probably not do what you describe since the ring-trip relay would have operated, a call manually placed through an operator (who had no ring-trip supervision) could result in *exactly* what you describe. <> Larry Lippman @ Recognition Research Corp. - Uniquex Corp. - Viatran Corp. <> UUCP {boulder|decvax|rutgers|watmath}!acsu.buffalo.edu!kitty!larry <> TEL 716/688-1231 || 716/773-1700 {utzoo|uunet}!/ \uniquex!larry <> FAX 716/741-9635 || 716/773-2488