The article below offers some good advice to those having problems
with DSZ, ZCOMM or Unix Zmodem (rz/sz>.

>Path: lll-tis!oodis01!uplherc!utah-gr!stride!tahoe!adonis
>From: adonis@tahoe.unr.edu (Paul Graham)
>Newsgroups: comp.binaries.ibm.pc.d
>Subject: Re: DSZ Uploads
>Date: 7 May 88 21:12:39 GMT

[old article quotes deleted]

	More than likely, the problem is buffering in the network.
Zmodem is a streaming protocol, so it does not wait for a response
after each packet is sent.  This results in the networks buffers
becoming overridden fairly quickly.  (I would think that the reason it
takes longer in Boneill's case is that his network has larger
buffers.)  In order to force Zmodem to stop and wait for a response,
one must set the numeric parameter "w" to 1024 or so (depending on the
network).  This tells Zmodem to stop and wait every 256 bytes.  In
order to set it to 1024 (as an example) is to include in the command
line (before the "sz" or "rz", and after the speed and port settings)
"z pw1024".  Experiment with this number.  You want the largest number
that will allow transfers.  This will be different for every network.
I quote from the Zcomm manual in regard to this parameter:

	w	If non 0, restrict the ZMODEM transmitted window to the
	specified number of bytes.  Setting this parameter to N requests
	acknowledgements from the receiver every N/4 characters.  Pro-YAM
	[Zcomm and DSZ too (my insertion)] then waits for acknowledgements
	from the receiver whenever it has sent N more characters thean it
	has received acknowledgements for.  This parameter is uesful with
	networks with defective flow control, and with networks that store
	an excessive number of characters in transit.

Another parameter that might be useful is the "l" parameter, described
in the following:

	l	If non zero, forces ZMODEM to close a frame and wait for an
	ACK after each # bytes (default 0).  The frame length may be
	adjusted to prevent buffer overflow in data PBX systems.

Using one of these two parameters has given me error free transfers in
both directions through a Sytek network.  This is particularly
astonishing since the Zmodem program on the UNIX end thinks that we
are at 9600 baud, when actually, after going through the network,
things are at 1200 baud (ugh!).  Hope this helps.

-- 
-----------------------------------------------------------------------------
There are more important things to be    |        Derrick Hamner      
than responsible.  			    | {backbone}!tahoe.unr.edu!adonis