(defun broadcast-live-peers ()
  (broadcast (loop with t0 = (get-universal-time)
                   for s in stations 
                   when (< (- t0 (last-packet-timestamp s)) 30)
                     collect (operator s) into r
                   finally (return (format nil "live peers: ~{~a~^, ~}" (sort r #'string-lessp))))))