From: rick@ricksys.LoneStar.org (Richard McCombs)
Newsgroups: alt.bbs.waffle,comp.mail.uucp
Subject: Re: Zmodem NOT recommended (was Re: f,e-protocol in 1.65)
Date: Sun, 12 Apr 92 02:00:20 CDT
Reply-To: rick@ricksys.lonestar.org
Followup-To: alt.bbs.waffle comp.mail.uucp
Organization: The Red Headed League; Lawton, OK

Since this was discussed some in comp.uucp.mail, I  decided to crosspost
this to comp.mail.uucp and include it in the follow-ups, unless someone
has a problem with that.

david@csource.oz.au (david nugent) writes:

> pacolley@ember.UUCP (Paul Colley) writes:
> 
> > I would strongly recommend AGAINST using Zmodem for your UUCP
> > transport layer.  This is my opinion only, of course.
> > 
> > Zmodem works well for its intended purpose; user-supervised
> > uploads/downloads.
> > 
> > However, most UUCP communication is unsupervised.  Zmodem does not
> > require ANY ack's from the receiving system.  Zmodem is quite
> > capable of thus continuing to dump data for hours into a system
> > that has hung, died, modem unplugged from computer, etc.
> > Three window, 64-byte packet UUCP-g does far too many ack's at 9600
> > baud, but going to no acks at all is not a great solution.
> >
[...]
> 
> Yawn.
> 
> (sorry :-))
> 
> It's just that for the last 5 years I've been doing "unattended transfers"
> with FidoNet mailers using ZModem as the base file transfer protocol.
> Long distance (gasp!) transfers included. You can include me amongst the
> 16,000 odd FidoNet systems in the world and add another few thousand for
> members of other networks using the same technology.
> 
> Your claim is spurious. I'm not denying that there is a very real
> possibility that you're sending it a hung system, but in real life
> if doesn't often happen, or is usually accompanied by loss of carrier.
> If not, there is a timeout at the end of sending which takes care of
> things - the reality is that there is a real cost saving overall.
> 
> 
> 
> I see nothing wrong with a ZModem variant which is incorporated into
> uucico for systems that can use it. Certainly the error correction is
> better that uucp-g, so it's better for transfer of larger block sizes
> (there is a significant statistical difference between the error
> detection schemes), and the file resume capability, transparency
> over links using software flow control and auto-resizing of blocks
> to suit line conditions is definitely worth it.
> 

[Excuse my quoting so much of the above, but it'll give the readers of
comp.mail.uucp a chance to see what is being said.]

Mr. Colley may not know that Zmodem has a windowing mode and when used
in that mode it will ack but you can have the window big enough that it
won't ack as often as UUCP-"g".  Actually I don't think the Fidonet
mailers use the widowed mode for ZedZap but they seem to do all right.
Of course most of the systems that are calling long distance in Fidonet
are using some kind of hardware error control which would probably
prevent them from trying to send to a dead modem.
--
Internet: rick@ricksys.lonestar.org,      bo836@cleveland.freenet.edu
UUCP: ...!rwsys!ricksys!rick,   {backbones}!ricksys.lonestar.org!rick
BITNET: bo836%cleveland.freenet.edu@cunyvm  Fidonet: Richard McCombs @ 1:385/6
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