modems on RT (AIX 2.2.1)

[Robin D. Wilson/1000000]

In article <598 at vta.UUCP> tom at vta.UUCP (Tom Wiencko) writes:
>In article <WINDLEY.90Oct11083039 at cheetah.cheetah.cs.uidaho.edu> windley at cheetah.cs.uidaho.edu (Phil Windley/20000000) writes:
>>
>>
>>I'm trying to get an internal modem to work as a dial-in on an RT running
>>AIX 2.2.1.  The problem is that I can't find out how to send an
>>initialization string to it to get it to go into auto answer mode.  I've
>
>Send the following commands to your Hayes compatible modem:
>
>	E0
>	Q1
>	C1
>	D3
>

Actually the E0 is not required, but setting the port to pdelay or pshare is..	Setting Q1 is also not required, but setting Q1 OR Q2 is.

	1) E0 turns off command echo.  This means that when you type in
	commands on the modem, it will not respond.  This is to prevent 
	the modem from echoing back the login herald when the port sends
	it out.  Fortunately, if you use pshare, a login herald will not
	be issued until CD (carrier detect - rs232 pin 8) is raised by the
	modem.  Or, if you use "pdelay" the login herald will not be issued
	until the modem sends a character to the serial input on the RT.

	2) Q1 turns off command response from the modem.  This will work
	but it will cause problems if you need to use the modem for UUCP
	CU, or certain other facilities.  This is because these facilities
	(by default -- the configuration can be changed to work) use 
	the command response to detect call progress.  (Ie. send the command
	"AT", expect "OK" from the modem, dial the number, expect "CONNECT"
	from the modem, etc.)  Setting the modem to Q2 will cause the modem
	to only send responses to command issued from the RT side of the
	connection -- not the incoming telephone line side.  This will
	prevent the modem from saying "RING" or "CONNECTED" when the remote
	system dials in.  The reason you don't want these responses is because
	they will be stored on the serial input buffer as an attempt to login,
	causing the first login to always fail...  Not a good thing to 
	happen for reliable serial communications.

The C1 should read "&C1".  From my recollection (and from this hayes book
right here in front of me) there is no "C" software switch on the hayes
modems.  The "&C1" should set the modem to follow true carrier.  This is
very important if the tty is set to "pshare" since; when in pshare mode, 
getty will not issue a login herald until it sees carrier come up from the
modem.  If the modem is not set to "&C1" the modem will always hold carrier
high, causing getty to alwys issue a login herald (which defeats the purpose
of pshare).

The D3 should read "&D3".  The "D" software switch on the hayes modem is to 
alert the modem to "Dial".  The "&D" switch is to tell the modem how to 
handle DTR signals from the DTE device (the RT).  The "&D3" tells the modem
to hangup, and reset to stored operating parameters when DTR from the 
DTE device is dropped.  NOTE: this will dump any settings made to the modem
that you may have made without actually saving them to the default profile.
Another method to accomplish similar results is to set "&D2" instead.  This
will tell the modem to "hang up and return to command mode" when DTR is 
dropped by the DTE device.   This method will not reset the modem.   The 
reason this setting is significant, is that it will determine the modem's 
ability to hangup when the call is terminated by the RT.  The RT line
discipline currently will drop DTR for at least 10 milli-seconds after a
logout (or SIGKILL/SIGHUP/etc. on the process running on the tty) is received.
The response of the modem should be to drop carrier, to signal a loss of the
DTE device, and dropping CD should cause the modem to hangup.  This is very
important to modem communication because a connection will not hangup if 	the modem asserts DTR unless the remote site drops carrier.  (In other words,
if you logout on the RT, the connection will stay up until you physically 
disconnect the line from the remote site.)

Other important settings are:

	&K - sets flow control... NOTE: UUCP cannot use XON/XOFF flow
	control.  This is because UUCP transmits a packet, and then
	waits for a response (with a checksum of the received packet).
	The checksum value in the response packet can contain the valid
	XON/XOFF characters, and willbe stripped out by the modem, or the
	serial port drivers if used.  However, the RT cannot do RTS/CTS
	so you must set "&K0" if you want to use the RT - modem setup
	for UUCP.

		&K0 -- no flow control
		&K4 -- XON/XOFF flow control (can be used for "non-uucp"
					      connections.)

	Anything else won't work (reliably).

	S000 - set the number of rings before answering the call.  If you
	want the modem to autoanswer, set this to a number > 1.  Otherwise,
	0.  Be careful, large numbers will affect the timeout values for 
	incoming modems (ie. if the number of rings is set to "10" then,
	incoming calls will have to wait for 10-11 rings (about 45 seconds)
	before the remote modem will answer, add to that several seconds for
	negotiating carrier, and there is a good likelyhood that the default
	timeout on the remote modem for establishing carrier will be 
	exceeded, causing the remote modem to say "NO CARRIER" and hang-up.)

	The rest can be found in you modem book.



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