[OT] How to rsync images?

[Jeremy <thinker5555@yahoo.com>]

Greetings!

I've read that if I've downloaded a CD image and the MD5sum is wrong, then I
can use rsync to just get the parts that are different from the remote file.
I've read through the rsync manpage, but I still don't quite understand how
I'm supposed to use the command.  As an example, if there were to be an image
at ftp://ftp.debian.org/pub/iso/potato-1.iso (I know there's not, but I just need
a "for instance") then from what I've gathered, I'd use the command:

rsync -avz ftp.debian.org:pub/iso/potato-1.iso potato-1.iso

When I use this, though, I get timeout errors.  I know this can't be right,
but I'm not sure how I'm supposed to do it.  Could anyone offer any help with
this please?  I'd greatly appreciate it.

Thanks a bunch,
Jeremy