Summary: dialin + dialout on same device

From: Lester Ingber (
Date: Fri Dec 17 1993 - 04:02:53 CST

Summary: dialin + dialout on same device
I appreciate all the help given to me; I give acknowledgements at the
end. In the process of getting dialin + dialout on my ttyb device, I
did get more familiar with several aspects of my Sun SPARC-2 system.
The suggestions from most of these people was an integral part of the
solution, but the final resolution required additional specific tuning
than those suggested.
However, the problem ultimately seems to lie with a set of misleading
recommendations from AT&T; I do not know of any nicer or correct way of
saying this. I hope that they will at elast give more information in a
corrected FAQ.
>From the AT&T FAQ
11. Can AT&T modems support UNIX and uucp file transfers?
Yes, the DataPort and 3800 Series modems have straps in them for
support of UNIX applications.
Below are dialer scripts that have been tested to work in most UNIX
applications. These scripts are registered with NCR Unix software
development. There may be some cases where minor changes are
required but if entered into the dialers files EXACTLY as shown here,
they should work.
For 3700 with error correction:
att3700ec =+-, "" \M\dAT&F\r\c OK \dATQ2&C2\\D2\\Q2%C&W\r\c OK
For 3700 without error correction:
att3700noec =+-, "" \M\dAT&F\r\c OK \dATQ2&C2\\D2\\Q2\\N&W\r\c OK
For 3800 with error correction:
attparadyne.3800ec =+-, "" \M\dAT&F3\r\c OK \dAT&D2%C&W\r\c OK
For 3800 without error correction:
attparadyne.3800noec =+-, "" \M\dAT&F3\r\c OK \dAT&D2\\N&W\r\c OK
I have a new external AT&T 3721 enhanced with V.17 capability.
First, as two At&R technicians admit, there does not seem to be any
rationale for have %C in the first set of instructions; %C is
equivalent to %C0. %C0: "This setting disables the use of V.42 bis
and MNP 5 data compression."
Second, and relevant to my problem to have dialin and dialout on the
same device, &C2 seems quite inappropriate if the modem is to be used
by most people, including UNIX people.
>From page 3-11 of the DataPort Modem User's Guide, dealing with
&Cn for CD (carrier detect):
&C0: This setting forces CD on at all times. This is known as
\f3Forced ON.\f1 This is the default setting for the external modem.
&C1: This setting allows CD to operate as stated in the EIA RS232
standard. CD turns on when the remote modem's carrier signal is
detected. CD is off when the carrier signal is not detected. This is
the default setting for the internal modem.
&C2: This setting forces CD ON, but turns if Off for approximately one
second when the modem disconnects. \f3This is known as Wink When
Clearly &C0 (the default for the external modem) or &C1 (the
recommended setting for UNIX systems) messes up the capability to
dialin and dialout on the same device. The proper setting should be
&C2, and in fact this does work!
While I still may have more surprises/problems ahead to port some fax
software, here are my current system settings.
ingber% ps -ax | grep gett | grep -v grep
  828 ? IW 0:00 - std.38400 ttyb (getty)
ingber% ls -ls /dev/cua1 /dev/ttyb
   0 crw-rw-rw- 1 uucp wheel 12,129 Dec 17 04:05 /dev/cua1
   0 crw--w--w- 1 root wheel 12, 1 Dec 16 20:13 /dev/ttyb
ingber% eeprom
In /etc/ttytab:
#ttyb "/usr/etc/getty std.38400" dialup off remote
ttyb "/usr/etc/getty std.38400" dialup on remote secure
#cua1 "/usr/etc/getty std.38400" unknown off remote secure
In /etc/gettytab:
In /etc/remote:
Brian Leimbach <>
Chris Elvin <>
Geoff Coleman <>
Glenn Newell <>
Guy Harris <>
Jim Mintha <>
Richard Cheung <>
Wietse Venema <>

|| Prof. Lester Ingber                                                ||
|| Lester Ingber Research                                             ||
|| P.O. Box 857                     E-Mail: ||
|| McLean, VA  22101             Archive: ||

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