A major goal of the BcN (Broadband Convergence Network) is to facilitate convergence of networks and services. Many transport-related technologies were considered. One technology discussed is ATM (Asynchronous Transfer Mode) based MPLS (Multi-protocol Label Switching) for its provisioning QOS (Quality Of Service) commitment, traffic management aspects and smooth migration to the BcN in Korea. In this paper, we present preventive congestion control mechanisms for detecting RPC (Rare Probability of Connection) LSP (Labeled Switched Path) in ATM based MPLS systems. In particular, we introduce a RPC LSP detection method using network signaling information. RPC LSP control can handle 208% call processing and more than 147% success call, than those without control. It can handle 187% BHCA (Busy Hour Call Attempts) with 100 times less use of exchange memory. We concluded that it showed fast congestion avoidance mechanism with a lower system load and maximized the efficiency of the network re...