The other guys will correct me if I'm wrong. This is how it has been explained to me. Think of Time Slots as concurrent licenses. You can load each cabinet to the gills. As an extreme example, 7 IPRCs w/daughter cards would be 224 devices in a single cabinet. The cabinet will only support 128 actively in use. The 129th device to go active, will not work. So the question is, if you go over the 128, what are the odds that the cabinet will need more at any given time?