From:	SMTP%"lail@trayce.mko.dec.com"  2-FEB-1995 15:22:05.77
To:	EVERHART
CC:	
Subj:	Re: The endless MODEM <-> LAT question

From: lail@trayce.mko.dec.com (bob lail)
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Subject: Re: The endless MODEM <-> LAT question
Date: 2 Feb 1995 15:54:00 GMT
Organization: Digital Equipment Corporation, Merrimack, NH, U.S.A.
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Andreas

A couple of comments on your file transfer problems with a DECserver 200/MC and
KEAterm 340. 

	1) The DECserver 200/MC does not support true RTS/CTS flow control. The
EIA RTS and DTR signal lines are tied together so when modem control is enabled 
the server drives the RTS and DTR lines as defined for EIA DTR. When Modem 
Control is disabled then DTR and RTS are driven as hardware flow control if
enabled. Our newer DECservers, the DECserver 700-8 (and -16) and DECserver 
900Tm correctly support RTS/CTS flow control.

	2) With your current port set up you can enable RTS/CTS flow control. 
Use the command:

	SET/DEFINE PORT 8 FLOW CTS

Be sure you disable the modems response to DTR with the AT&D0 command enable
the modem to respond the hardware flow control. Of course not having modem
controls enabled on the server make disconnecting and dial-in though this port
difficult at best but for your application hardware flow control is really the
best way to go.

	3) Even though modern versions of the ZMODEM protocol have been "fixed"
to allow for "XON/XOFF" support I have never had good luck with using ZMODEM
with XON/XOFF flow control. It is possible that one of the versions of ZMODEM,
either the KEAterm implementation or the BBS, does not have the XON/XOFF "fix"
and when you try to upload the server sucks up XON/XOFF characters and causes
the transfer to fail. Download may work because the bit rate difference between 
modem real link rate and DECserver/modem serial link rate is small enough that
the server never issues and flow control. At the BBS end the difference between
the modem link rate and the BBS/modem serial line rate may be much larger such
that during an upload flow control is attempted and data gets lost causing 
ZMODEM to timeout and abort the transfer.

	4) As you stated you may have something set wrong in the Worldport modem.
Make sure the modem is not swallowing XON/XOFF characters or generating them
on its own. 

Hope this helps

	\Bob Lail

--------------------------------------------------------------------------
Robert G. Lail         Digital Equipment Corp     NET: lail@trayce.mko.dec.com
Hardware Engineer      Digital Drive              TEL: 603.884.7161 
Custom Systems PSC     Merrimack, NH 03054-9501   FAX: 603.884.4343
                       LOC MS: MKO1-1/A10
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