Xref: utzoo comp.binaries.ibm.pc.d:1662 comp.sys.ibm.pc:22700
Path: utzoo!utgpu!watmath!clyde!att!rutgers!mailrus!purdue!haven!umbc3!cs374326
From: cs374326@umbc3.UMD.EDU (Peter Johansson)
Newsgroups: comp.binaries.ibm.pc.d,comp.sys.ibm.pc
Subject: Re: DSZ rz & sz
Summary: Zmodem block size
Message-ID: <1516@umbc3.UMD.EDU>
Date: 3 Jan 89 09:49:26 GMT
References: <54@VAX1.CC.UAKRON.EDU> <2919@uhccux.uhcc.hawaii.edu>
Reply-To: cs374326@umbc3.UMD.EDU (Peter Johansson)
Distribution: na
Organization: University of Maryland, Baltimore County
Lines: 36

In article <2919@uhccux.uhcc.hawaii.edu> julian@uhccux.uhcc.hawaii.edu (Julian Cowley) writes:
>In article <54@VAX1.CC.UAKRON.EDU> Gregg Thompson writes:i]
>>	Now how does one get rz and sz on Unixand dsz sz & rz to work at
>>1024 blocks??  On bulliten boards I can upload and download at 1024 blocks
>>just using standard commands with dsz (dsz rz and dsz sz), but when it comes
>>to the Unix system it doesn't send or receive at 1024 characters a block!?!?!
>>Ideas???
>
>Actually, the block size you are referring to is known as the
>subpacket size, because the subpacket may or may not elicit a
>response from the receiver, unlike an X/Ymodem block which always
>elicits a response.  [ rest deleted ]

I don't want to steer anyone in the wrong direction since I've never read
the Zmodem manual, but the following have been my experiences.  I am
using the version of zmodem available from simtel-20 in the unix-c archives,
(v1.36) compiled on a vax 11/785 running Ultrix 2.0-1, and it defaults to
a packet size of 1024 bytes at 2400 baud.  It is possible that your system
has an older version of sz/rz (I seem to remember the packet size to baud
rate ratio different on older versions) or that your copy was edited
before it was compiled.  It is also possible that your sz command is
aliased to 'sz -L 512' or something similar (an environment variable set
to '-L 512') to allow data to pass through your terminal server(s).

But in the end, it really shouldn't matter all that much.  Remember, the
only disadvantage to a small packet size in Zmodem is the overhead (header,
CRC, etc) for each packet, and you do not have to worry about inter-packet
delays as you do with x- and y-modem.  Unless, of course, you have a
severely brain damaged server that requires ACK's (or whatever code
zmodem uses (don't flame me to RTFM)) after each packet to keep the server
happy.  (I have to use sz -l 1024 -L 1024 <filename>, for example)

BTW, a newer version of sz/rz compiled under VMS 4.7 on a VAX 8600
(I don't remember which version; I don't use it very much as the
port to vms left it rather buggy) does indeed limit the packet size
to 512 bytes at 2400 baud.