Automatically resume rsync over SSH after broken connection

perpetual-rsync.sh

#!/bin/bash

while [ 1 ]
do
    rsync -avz --partial source dest
    if [ "$?" = "0" ] ; then
        echo "rsync completed normally"
        exit
    else
        echo "Rsync failure. Backing off and retrying..."
        sleep 180
    fi
done

What is rsync is running but the transfer has stopped for some reason but rsync has not exited?