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This study investigates routing in a MPLS-based (multi-protocol label switching) IP network with heterogeneous holding time traffic (for example, an IP call versus an IP conference). Our basic idea is to exploit the large differences existing in the holding time of different types of traffic to make more efficient resource allocation decisions in the admission and routing processes. In particular, we investigate the concept of vacating, in which requests with short holding times vacate the bandwidth to requests with long holding times. Based on an analytical framework we developed, we analyze the vacating idea and propose several state-dependent routing schemes, namely preventive-vacating routing (PW), preemptive-vacating routing (PEV) and restricted-access routing (RAR). Both the analytical and simulation results indicate that within an effective range we found in traffic mix, our vacating schemes outperform the traditional LLR+TR (least loaded routing+trunk reservation) and Diff-SDR (differentiated dynamic shortest-distance routing scheme) S. Yang et al., (2001). Moreover, we deduce an approximated expression to compute the cost of accepting a long or short request, which leads to an approximated least cost routing (A-LCR) scheme. Through simulation study, A-LCR presents not only its good performing in network throughput, but also its particular flow control mechanism.