Each receiver host sends reservation request (Resv) messages upstream toward senders and sender applications. Resv messages must follow exactly the reverse path of path messages. Resv messages create and maintain a reservation state in each router along the way.
Resv messages are sent periodically to refresh reservation states. The refresh interval is controlled by the same refresh time variable, and reservation states are kept for ( (keep-multiplier + 0.5) x 1.5 x refresh-time ) seconds.