Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!thunder.mcrcim.mcgill.edu!snorkelwacker.mit.edu!usc!cs.utexas.edu!uunet!munnari.oz.au!brolga!bunyip.cc.uq.oz.au!marlin.jcu.edu.au!zlraa
From: zlraa@marlin.jcu.edu.au (Ross Alford)
Newsgroups: comp.sys.handhelds
Subject: Re: Zmodem
Message-ID: <1991Jan31.073919.27350@marlin.jcu.edu.au>
Date: 31 Jan 91 07:39:19 GMT
References: <1991Jan31.015953.18380@csn.org>
Organization: James Cook University of North Queensland
Lines: 38

In article <1991Jan31.015953.18380@csn.org> frechett@spot.Colorado.EDU (-=Runaway Daemon=-) writes:
>
>We need Zmodem.  I know this sounds crazy but so does most of the other 
>things that have been done on the hp48sx.  ;)  After spending several hours 
>with my hp48 plugged into the back of a Sun, logged into another computer and 
>kermiting stuff all over hell, and back, I find that kermit sucks.. 
>Gotta love the error checking but it sure makes it slow.  I didn't time
>it but I just did an archive of my calculator (1220 kermit packets) and 
>it was dreadfully slow.  And that was at 9600 baud.  I can't imaging how long
>it would take to do at 2400 baud over the modem at home.  (No PC)
>
Believe it or not, it wouldn't take much longer.  The overhead in a
Kermit transfer is apparently so high that baud rates above 2400 don't
really seem to speed things up too much.  The packets in standard Kermit
are limited to a maximum of something like 92 bytes, and *lots* of
handshaking is done for each packet.  I do a lot of file transfers
between my laptop and a Decstation, and have timed it at about 8-10
kbytes/minute at 9600 baud, which is astonishingly bad.  At 2400 baud it
runs much closer to the potential bit rate, but still only about 65% or
so.

I doubt that changing the packet-check type would make much difference.
What would make a difference is incorporation of a Kermit protocol that
allowed extended-length packets.  The latest versions of C-Kermit and
MS-Kermit both allow packets to be up to 1024 bytes long.  Setting
packet-length to a large size improves my laptop transfer rate to about
20k bytes/min at 9600 baud.  Still only about 40% or so of what's
possible, but a real improvement.

I now use Ymodem for my laptop.  Ymodem uses 1024 byte packets and
obviously has a lower overhead/packet that Kermit, since it runs at
about 50kbytes/minute over a 9600 baud serial line.  It has the
advantage over Zmodem that it is *much* easier to implement, ends up
being much smaller, and is neraly as fast if bit errors are rare.  I'd
suggest it for a HP extension over Zmodem for those reasons.

Ross Alford
zlraa@marlin.jcu.edu.au