Slow down incoming rsync/scp connections

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http://serverfault.com – I have a server to which several other servers upload large files on a regular basis through rsync and scp. Several of them can upload fast enough to max out my server's internet connection, slowing things down for everything else. How can I force them to go slower from my end? I can't make them to change anything on their systems, so using rsync's bwlimit option isn't possible. All the systems have static IP addresses, so identifying them isn't a problem. Is there anything I can do with iptables or something similar to slow them down and free up my internet connection? ()