[linux-help] Re: Serial data transfer -

[Steven Saner <ssaner@xxxxxxxxxxxxxxx>]

On Fri, Nov 17, 2000 at 10:30:12PM -0600, Greg House wrote:
> On Fri, 17 Nov 2000, you wrote:
> > > You could also use xmodem, ymodem, zmodem (pick any one, zmodem does the 
> > > best
> > > compression, I believe). The easiest way is to establish your link and 
> > > login
> > 
> > None of those do *any* compression.  Zmodem has the best error correction
> > (CRC vs. Checksum) of those three, though.
> 
> Hmm.. I always thought they did. If it's not compression, then what's the
> difference between them (obviously, other then the error correction...)
> 
> Greg

Well the error correction is quite important since xmodem and ymodem
have very little. zmodem also has a few other nice features. One such
thing is that the protocol provides "AutoDownload". If your terminal
client supports it, when you do an sz on the host, the client will be
able to detect that a file is coming via zmodem and automatically
launch the recieve process. Another difference is efficiency. zmodem
transfers larger blocks at a time than, say xmodem, and is generally
faster. If you have just a serial connection (cable or modem) a zmodem
transfer is probably the fastest way to transfer a file between two
systems. Quite a bit faster than ftp over a PPP link (although if the
file isn't very large, you won't notice much difference, and I suppose
if you have some PPP compression going on you might be able to argue
against this point).

A note about compression. If you are using zmodem to transfer a file
with an analog modem, you may get some compression because the modem
protocols have compression algorithms built into them (MNP5, V.42bis,
etc.)

Steve

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