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From: jbn@glacier.ARPA (John B. Nagle)
Newsgroups: comp.dcom.modems
Subject: Re: An interesting modem problem
Message-ID: <13258@glacier.ARPA>
Date: Wed, 26-Nov-86 13:13:04 EST
Article-I.D.: glacier.13258
Posted: Wed Nov 26 13:13:04 1986
Date-Received: Wed, 26-Nov-86 20:38:30 EST
References: <128@gaia.UUCP> <4070001@hpscda.HP.COM> <18@ucdavis.UUCP> <418@catnip.UUCP> <117@devon.UUCP> <3048@milano.UUCP>
Reply-To: jbn@glacier.UUCP (John B. Nagle)
Organization: Stanford University, IC Laboratory
Lines: 13
Keywords: CTS 2424ADA


      Somebody misunderstands the meaning of the RS-232 Data Set Ready
signal.  Data Set Ready is supposed to indicate that a modem is attached,
powered up, not in some self-test or loopback state, and otherwise a
functional unit.  It does NOT indicate that any kind of communication has
been established with the other end.  The Carrier Detect signal indicates
that modem-to-modem communication has been established.  Lack of DSR is
properly an indication of strictly local trouble.
      I realize that microcomputer vendors tend to be pretty casual about
the RS-232 standard, but those signals have clear meanings in the modem
context.

					John Nagle