Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!accuvax.nwu.edu!nucsrl!telecom-request From: Gary Segal Newsgroups: comp.dcom.telecom Subject: Re: Telephone Diverters Message-ID: <10763@accuvax.nwu.edu> Date: 12 Aug 90 18:37:03 GMT Sender: news@accuvax.nwu.edu Organization: Motorola INC., Cellular Infrastructure Division Lines: 41 Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 10, Issue 563, Message 7 of 12 dave%westmark@uunet.uu.net (Dave Levenson) writes: >What in the world is "reverse modem detection"? The originating modem >remains silent, expecting answer-tone from the answering modem? Here is a guess ... The device is looking for V.25 calling tone. V.25 is the CCITT's version of a modem command set (like the "AT" set we all know and love), but it also includes a provision for calling tone similar to what Fax machines use. It is supposed to be used on all automaticly dialed calls by modems (i.e. whenever the equivalent of "ATD..." is sent). For those who want more details, V.25 describes the tone as a "1300 Hz or any tone corresponding to binary 1 of the DCE in use." It is on for 0.5 to 0.7 seconds, and then off for 1.5 to 2 seconds. Fax calling tone, on the other hand, is an 1100 Hz tone, on for 0.5 seconds and off for 3 seconds. >As far as I know, some fax machines, in some originating modes, >generate the CNG tone when they're awaiting answer. I know of no >non-fax modems that would work with the device described above. All fax machines are supposed to generate calling tone when the machine dials. If an autodialing fax machine doesn't generate calling tone (CNG), it is in violation of the T.30 recommendation for fax machines. Since there are some data modems that are V.25bis or V.25 compliant, there is a small chance that the "telephone diverter" in question is designed to use both Fax CNG and modem CNG as a means to route calls. However, the device in question would probably not work to well if it is looking for modem calling tone, as very few modems in the U.S. have the ability to generate it. Gary Segal ...!uunet!motcid!segal +1-708-632-2354 Motorola INC., 1501 W. Shure Drive, Arlington Heights IL, 60004 The opinions expressed above are those of the author, and do not consititue the opinions of Motorola INC.