Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!uwm.edu!rpi!zaphod.mps.ohio-state.edu!unix.cis.pitt.edu!gvlv2!faatcrl!jimb
From: jimb@faatcrl.UUCP (Jim Burwell)
Newsgroups: comp.sys.amiga
Subject: Re: Send ZModem and JRComm
Message-ID: <1423@faatcrl.UUCP>
Date: 2 Jun 90 00:32:34 GMT
References: <4926@daffy.cs.wisc.edu>
Distribution: usa
Organization: FAA Technical Center, Atlantic City NJ
Lines: 45

upl@gumby.cs.wisc.edu (Undergrad Projects Lab) writes:

>I'm currently using JRComm at home on my A-500, and use a VAX down at the
>university.  I want to transfer software using ZModem, since it's much faster
>than the dreaded Kermit.

>Anyway, using JRComm's and the Unix's (yeah, the VAX is running UNIX), everything
>goes fine until I get to 2048 characters.  Then, I get a "Data Sub Packet too
>long" message (ALWAYS!), and the machines kind of dink around until they
>become re synchronized.  Generally, this results in a net time of about half
>an hour to transfers a 50K file!  (ARGH!)  

[stuff deleted]


This looks like a flow control problem.  Is the dialup you're using a serial-port
on the CPU, or is it a terminal server ?  

If the case is the former, and your Vax is running a 4.2 BSD derivitive, and the 
modems/cables are configured for hardware handshaking, do an "stty crtscts".  
Actually, the "crtscts" ioctl may be SunOS 4.x specific, so it may not exist on 
your system.  

If the case is the latter you must turn on some sort of flow control on the
terminal server.  Every manufacture has a different way.  (on our Cisco box, it's
"term flowcontrol none|hardware|software  [in|out]")  Of course, hardware
flow control is preferable, but the modem/cable must also be set for that.

The bottom line is that for Zmodem to work reliably over an MNP (or PEP, for that
matter) connection, you must have some sort of flow control enabled.  If you
don't, the modem's buffer could overflow if the modem gets behind transmitting
its data to the other modem (due to block retransmits, or if you run asymetrical
data rates between the modem and DTE).  

If you need any help configuring Cisco boxes or Suns for hardware flow control,
you can send me some mail..

C'ya,
Jim
 
-- 
James S. Burwell
UUCP:  ...!rutgers!faatcrl!jimb        Internet:  jimb@faatcrl.UUCP
"The Maker is the one who is part of what he makes." - The Redbird, from
                                                  _The Tales of Alvin Maker_