Getting nowhere syncing a download

[bob parker]

I must be doing something wrong with this, but I am trying to correct a 
downloaded iso which does not match the source md5sum.

This is what I do:

rsync rsync://ftp.gwdg.de/pub/linux/knoppix/KNOPPIX_V3.1-2003-01-20-EN.iso 
KNOPPIX_V3.1-2003-01-20-EN.iso

The command returns in a few seconds without any error message and nothing 
has changed with the md5sum on my copy.

What am I doing wrong?

Thanks
Bob