Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!maryland!oddjob!uwvax!husc6!yale!bunker!wtm From: wtm@bunker.UUCP (Bill McGarry) Newsgroups: comp.dcom.modems Subject: Information on TDD's (1 of 3) Message-ID: <1997@bunker.UUCP> Date: Thu, 30-Apr-87 21:50:23 EDT Article-I.D.: bunker.1997 Posted: Thu Apr 30 21:50:23 1987 Date-Received: Sat, 2-May-87 14:42:14 EDT References: <4262@fritz.UUCP> <1987@bunker.UUCP> Reply-To: wtm@bunker.UUCP (Bill McGarry) Distribution: na Organization: Bunker Ramo, an Olivetti Company, Shelton, CT Lines: 125 These three articles are taken from the Handicapped Educational Exchange (HEX) bulletin board (301-593-7033, 300 Baud). These articles will be posted on a periodic basis in the misc.handicap news group. Other information, comments, questions, etc, on TDD's are posted in the misc.handicap news group and the Handicap Digest mailing list. Thanks to Dick Barth, the sysop of the HEX BBS for these articles. Bill McGarry Moderator Handicap Digest/News Bunker Ramo, Shelton, CT (203) 337-1518 PATH: {philabs, decvax, fortune, yale}!bunker!wtm TELECOMMUNICATIONS DEVICES FOR THE DEAF (Posted April 30, 1987) There are over 3000 Telecommunication Devices for the Deaf in use in the greater Washington D.C. area and estimates range as high as 25,000 nationally. The deaf have been using these devices for over fifteen years, to communicate among themselves and more recently, with a growing number of organizations with TTY numbers to allow phone access to deaf users. See the INFO files for some numbers. Although originally the majority of devices were surplus "teletype" machines donated by the phone company and the military, these mechanical printers are rapidly being replaced by more modern devices offering special features as well as reductions in size and weight. A portable device about the size of a calculator is available for under $200. The following shows the differences between the modems used. The owner of a computer can rather easily modify his software to convert between the ASCII code used in microcomputers and the code used by the deaf TTY. Often, it is harder to get a modem which is compatible both with a computer and with the TTY. The usual procedure is to convert an ASCII (Bell-103 compatible) modem or build a TTY modem from scratch. There are several differences between protocols used by ASCII terminals and by the TTY. The following attempts to clarify these. ASCII DATA DEAF TDD FEATURE COMMUNICATIONS COMMUNICATIONS ------- ------------------ -------------- CODE ASCII Baudot SPEED 110/300 baud 45.45 baud MODE full/half-duplex 2 way simplex MODEM Bell 103 ORIG/ANS Weitbrecht MARK ORIG 1270 Hz 1400 Hz ANS 2225 Hz SPACE ORIG 1070 Hz 1800 Hz ANS 2025 Hz In the Weitbrecht modem, tones are only transmitted for the duration of the character so the line is available for transmission in either direction. In practice the mark tone is retained for as much as a half second before being squelched. Notice also that the mark is high for the Bell 103 and is the low tone for the Weitbrecht. This means that in converting a a Bell 103 modem to TTY use, the data will be inverted from RS-232 and the mark hold circuitry will need to be inverted. Line supervision is also different in these modems. In -103 protocol, the presence of the tone carriers gives positive indication of the status of each end of the link. In the Weitbrecht case, however, the absence of tones except while characters are being transmitted results in there being no positive way to test the status of the other end of the communications link. To aid the deaf, a lamp is provided on most Weitbrecht modems which varies in intensity proportional to signals on the line so that the ringing and busy signals are recognizable. Federal Government numbers ____________________________________________________________ Deafness and Communications Dis. 202 245-0591 Department of the Treasury 202 287-4097 Internal Revenue Service (toll free) 800 428-4732 Merit Systems Protection Board 202 653-8896 Nat'l Air & Space Museum (24 hours) 202 357-2853 National Ocean Atmospheric Administration 301 427-7627 President's Comm on Employment of H'capped 202 653-5337 Smithsonian Institution 202 381-4233 Social Security 800-325-0778 MO] elsewhere 800 392-0812 U.S. Government Printing Office 202 541-2977 U.S. Department of Commerce 202 377-5588 U.S. Senate 202 224-5644 USOE Office of Special Education 202 472-1356 White House - GEN. INFO 202 456-6213...TOURS 202 456-2287 National TTY numbers (non-government) ____________________________________________________________ TTY Assistance Operator (toll free) 800 855-1155 American Express Co American Express TOLL FREE (outside NY) 800-221-9950 TOLL FREE (inside NY) 800-522-1897 The above numbers are answered 9AM-5PM Eastern. The following are for refunds of AMEX travelers checks, and operate 24 hours a day. TOLL FREE (outside NY) 800-221-9986 TOLL FREE (inside NY) 800-522-5538 American Airlines 800-582-1573 in Ohio- else 800 543-1586 United Airlines (toll free) 800 323-0170 TWA 800-252-0622 in Calif] elsewhere 800 421-8480 Greyhound Bus (toll free) 800 345-3109 AMTRAK (toll free) 800 523-6590 Deaf Crisis Center (toll free) 800 446-9876 Deaf Counseling Ctr (toll free) 800 446-5000 Western Union 800 392-1474 in MO] elsewhere 800 325-4108 Boston DEAFNET (DCI) 617-975-0354