larry@uunet.uu.net (Larry Lippman) (08/01/90)
In article <10235@accuvax.nwu.edu> gammafax!mikes@uunet.uu.net (mike spann) writes: > I have seen two common types phone/fax switch boxes. > The other box (and the one I would select) uses the little known fact > that audio energy is carried down the phone line when the phone is > ringing. (This is commonly known to thiefs who sometimes talk to each > other without answering the phone). An automatic fax machine sends a > calling tone every three seconds while waiting for the phone to be > answered. The phone/fax switch box listens on the line for this > 'calling tone' and routes the call to the fax machine if one is heard. > The box never answers the phone which I consider an advantage. This > way you can have a real-live phone the voice connection and a fax > machine on the other. People don't have to pay to call when you > aren't home. With the exception of certain electromechanical CO's such as SxS, XY and No. 1 XBAR (probably not No. 5 XBAR unless it is *really* old), there is *no* audio path created between the calling and called parties prior to answer and ring trip. No commercial telephone/fax switch box would rely upon a mode of operation which probably exists in less than 5% of all CO's in North America. Such an audio path only existed when audible harmonics from ringing current were coupled back to the calling party using a capacitor to provide ringback tone. Such ringback tone varied in intensity with the called party loop length and number of connected ringers, creating a disadvantage. The use of the CCITT 440/480 Hz tones for ringback required a separate ringback tone generator and a different circuit which no longer created the above audio path. Most No. 5 XBAR CO's were modified during the 1960's to provide the above precise ringback tone. What the above telephone/fax switch boxes do is answer the line as soon as possible (i.e., on the first ring), and then supply their *own* ringback tone. Therefore, not only is an audio path created by conventional answer, but the call is certainly not "free". Larry Lippman @ Recognition Research Corp. "Have you hugged your cat today?" {boulder||decvax||rutgers||watmath}!acsu.buffalo.edu!kitty!larry VOICE: 716/688-1231 || FAX: 716/741-9635 {utzoo||uunet}!/ \aerion!larry
David E A Wilson <david@cs.uow.edu.au> (08/02/90)
kitty!larry@uunet.uu.net (Larry Lippman) writes: >Such an audio path only >existed when audible harmonics from ringing current were coupled back >to the calling party using a capacitor to provide ringback tone. Such >ringback tone varied in intensity with the called party loop length >and number of connected ringers, creating a disadvantage. The use of >the CCITT 440/480 Hz tones for ringback required a separate ringback >tone generator and a different circuit which no longer created the >above audio path. Most No. 5 XBAR CO's were modified during the >1960's to provide the above precise ringback tone. Here in Australia, I have noticed that with my parents phone, the ring sound that the caller gets depends on the phone plugged into the socket (phones that chirp and phones that ring a bell sound different to the caller). Would this tend to indicate the vintage of their exchange? David Wilson Dept Comp Sci, Uni of Wollongong david@cs.uow.edu.au