SURF_CPU_LEVEL = xbt_lib_add_level(host_lib,surf_cpu_free);
SURF_WKS_LEVEL = xbt_lib_add_level(host_lib,surf_workstation_free);
SURF_LINK_LEVEL = xbt_lib_add_level(link_lib,surf_link_free);
SURF_CPU_LEVEL = xbt_lib_add_level(host_lib,surf_cpu_free);
SURF_WKS_LEVEL = xbt_lib_add_level(host_lib,surf_workstation_free);
SURF_LINK_LEVEL = xbt_lib_add_level(link_lib,surf_link_free);