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CC:	
Subj:	Re: ZModem and Xmodem

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Date: 12 Jul 90 19:16:29 GMT
From: vax8530!bqsy1@cu-arpa.cs.cornell.edu
Subject: Re: ZModem and Xmodem
Message-Id: <4606.269c944d@vax5.cit.cornell.edu>
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> 	What I need to know is if it is possible to operate XMODEM or
> ZMODEM successfully with no xon/xoff, and if so, how have people made out
> who have done so? And what version of VMS XMODEM or ZMODEM did you start
> with?
> 	Andrew Orndorff
>         Internet: bqsy1@vax5.cit.cornell.edu

Here at Hayes, we have been using XMODEM and ZMODEM for quite some time.
Recently we changed from Interlan terminal servers to DEC terminal servers,
and ZMODEM stopped working.  The problem was this:

The ZMODEM program turns off hostsync, but the Interlan boxes don't respect
the change.  Thus, flow control was not really being turned off, so ZMODEM
worked fine.

The DECservers are smarter, so they actually turn off flow control when
the VAX requests it.  The PC's were sending data faster than the DECservers
could handle it, so ZMODEM didn't work.  As near as I can tell, the DECservers
have a 128-byte buffer, which is large enough for XMODEM but not for ZMODEM.

I changed the code in vrzsz.c so instead of turning off hostsync and setting
pasthru, it enables hostsync and sets passall.  Inside rz.c it says that
the version is 3.01, from 25-May-89.  sz.c says version 3.03, 9-May-89.
Here's a diff of vrzsz.c:

************
File USER$DISK:[MSIEWEKE.ZMODEM]VRZSZ.C;4
                parameters      |=  TT$M_HOSTSYNC;      /*  HOSTSYNC ON   */
                parameters      |=  TT$M_NOECHO;        /*  NOECHO   ON   */
                parameters      |=  TT2$M_PASTHRU;      /*  PASTHRU  ON   */
                parameters      &= ~TT$M_READSYNC;      /*  READSYNC OFF  */
******
File USER$DISK:[MSIEWEKE.ZMODEM]VRZSZ.C;3
                parameters      &= ~TT$M_HOSTSYNC;      /*  HOSTSYNC OFF  */
                parameters      |=  TT$M_NOECHO;        /*  NOECHO   ON   */
                parameters      |=  TT$M_PASSALL;       /*  PASSALL  ON   */
                parameters      &= ~TT$M_READSYNC;      /*  READSYNC OFF  */
************

Number of difference sections found: 1
Number of difference records found: 3

DIFFERENCES /IGNORE=()/MERGED=1/NONUMBER-
    USER$DISK:[MSIEWEKE.ZMODEM]VRZSZ.C;4-
    USER$DISK:[MSIEWEKE.ZMODEM]VRZSZ.C;3

With these changes, ZMODEM works over DECservers.  One of the users claims
that uploads to the VAX run slow, but I haven't had any other complaints.

According to the guy who uses ZMODEM, it was designed so it doesn't use the
xon/xoff characters.  However, XMODEM _does_ use these characters, and it
won't work if you have xon/xoff flow control enabled.  In your situation
it sounds like you won't get XMODEM to work.  You should concentrate on
ZMODEM.

I hope this helps.  BTW, you can post this if you wish.

Mike Sieweke                            ...!uunet!hayes!msieweke
Hayes Microcomputer Products            msieweke@hayes.uucp
Norcross, Georgia                       hayes!msieweke@uunet.uu.net

