Following your installation plan, use a tape measure and marking pen to measure and mark space on each equipment rack for each router component. For horizontal spacing follow Network Equipment Building System (NEBS) requirements. To maintain airflow requirements, a plenum must be installed above the E320 router before any piece of equipment (other than an E320 router) is installed above the router. If you choose not to install a plenum, be sure to include 2 U of space between the E320 router and the other component for proper exhaust. A plenum, however, is highly recommended.