Network Service – a capability that facilitates a network operation. It typically is provided by a server (which can be running one or more services), based on network protocols running at the application layer in the Open Systems Interconnection (OSI) model of the network. Some examples are domain name system (DNS), dynamic host configuration protocol (DHCP), voice over internet protocol (VoIP), etc.
As defined by Network Functions Virtualization (NFV) ETSI Industry Specification Group (ISG) in the Network Functions Virtualisation (NFV); Terminology for Main Concepts in NFV, a network service is a composition of network functions and defined by its functional and behavioral specification.
NOTE: The network service contributes to the behavior of the higher layer service, which is characterized by at least performance, dependability, and security specifications. The end-to-end network service behavior is the result of the combination of the individual network function behaviors as well as the behaviors of the network infrastructure composition mechanism.