An interfacing system (400, 240) for establishing an interface between a transport network management system and a slice management system (220, 222) of a telecommunication network, wherein: - the transport network management system is configured for managing physical network equipment of a network having physical links, wherein the network supports instantiation of virtual networks over the physical links, and wherein the transport network management system is configured for administering, for a respective virtual network, via which one or more physical links traffic of the virtual network is routed, - the slice management system is configured for instantiating and managing network slices which each comprise one or more of the virtual networks, and wherein - the telecommunication network comprises a network virtualization system configured for instantiating virtual networks based on network service descriptions which represent respective network slices and administrating which one or more virtual networks are comprised in a respective network slice; characterized by the interfacing system comprising: - a data communication interface subsystem for communicating with the slice management system, the transport network management system and the network virtualization system; - a processor subsystem configured to, via the data communication interface subsystem: - obtain identification data from the network virtualization system, wherein the identification data identifies, for at least one network slice, which one or more virtual networks are comprised in the respective network slice; - based on the identification data, obtain utilization data from the transport network management system, wherein the utilization data is indicative of at least one of: a bandwidth capacity, computing capacity and storage capacity of one or more physical links via which traffic of the one or more virtual networks is routed; and - provide the utilization data for the at least one network slice to the slice management system. - the transport network management system is configured for managing physical network equipment of a network having physical links, wherein the network supports instantiation of virtual networks over the physical links, and wherein the transport network management system is configured for administering, for a respective virtual network, via which one or more physical links traffic of the virtual network is routed, - the slice management system is configured for instantiating and managing network slices which each comprise one or more of the virtual networks, and wherein - the telecommunication network comprises a network virtualization system configured for instantiating virtual networks based on network service descriptions which represent respective network slices and administrating which one or more virtual networks are comprised in a respective network slice; - a data communication interface subsystem for communicating with the slice management system, the transport network management system and the network virtualization system; - a processor subsystem configured to, via the data communication interface subsystem: - obtain identification data from the network virtualization system, wherein the identification data identifies, for at least one network slice, which one or more virtual networks are comprised in the respective network slice; - based on the identification data, obtain utilization data from the transport network management system, wherein the utilization data is indicative of at least one of: a bandwidth capacity, computing capacity and storage capacity of one or more physical links via which traffic of the one or more virtual networks is routed; and - provide the utilization data for the at least one network slice to the slice management system. - obtain identification data from the network virtualization system, wherein the identification data identifies, for at least one network slice, which one or more virtual networks are comprised in the respective network slice; - based on the identification data, obtain utilization data from the transport network management system, wherein the utilization data is indicative of at least one of: a bandwidth capacity, computing capacity and storage capacity of one or more physical links via which traffic of the one or more virtual networks is routed; and - provide the utilization data for the at least one network slice to the slice management system.