A resource orchestration entity of a Network Functions Virtualization, NFV, for enabling end-to-end service reliability and availability with service flow differential deployment of a network service by determining different service availability levels of different service flows with two or more service flows in a network service chain comprising two or more network function nodes , connected via intermediate networking nodes, wherein the resource orchestration entity is arranged to: obtain information elements of service availability level in a descriptor received from a network service management entity , wherein the information elements define the service availability level requirements of said different service flows in the network service chain; and provide the information elements of service availability level together with an identification reference of the respective service flow, to a resource management entity , for assigning resources comprising network function nodes and their inter-connections in virtual network laying on the network hardware comprising networking nodes, when instantiating the network service comprising the two or more service flows in the network service chain; characterized in that each information element: specifies a list of supporting service availability levels of the service flows; describes how to identify service availability levels of the service flows; and in case the service flow is identified with a transport layer identifier, a corresponding mapping between service availability levels and identifiers of quality of service, or class of service, is provided; wherein the descriptor is a network forwarding path embedding also the identification reference of the service flow; or the descriptor is a virtual link descriptor . obtain information elements of service availability level in a descriptor received from a network service management entity , wherein the information elements define the service availability level requirements of said different service flows in the network service chain; and provide the information elements of service availability level together with an identification reference of the respective service flow, to a resource management entity , for assigning resources comprising network function nodes and their inter-connections in virtual network laying on the network hardware comprising networking nodes, when instantiating the network service comprising the two or more service flows in the network service chain; characterized in that each information element: specifies a list of supporting service availability levels of the service flows; describes how to identify service availability levels of the service flows; and in case the service flow is identified with a transport layer identifier, a corresponding mapping between service availability levels and identifiers of quality of service, or class of service, is provided; specifies a list of supporting service availability levels of the service flows; describes how to identify service availability levels of the service flows; and in case the service flow is identified with a transport layer identifier, a corresponding mapping between service availability levels and identifiers of quality of service, or class of service, is provided; wherein the descriptor is a network forwarding path embedding also the identification reference of the service flow; or the descriptor is a virtual link descriptor . <EOS>