Network service topology: Formalization, taxonomy and the CUSTOM specification model

Network Function Virtualization (NFV) relies on virtualization technologies to allow the implementation of middleboxes in software that is executed on commercial off-the-shelf hardware. Multiple Virtual Network Functions (VNFs) can be combined to form arbitrary network services. The term service topology has been freely employed by both major NFV recommendation and standardization bodies (the Internet Engineering Task Force (IETF) and European Telecommunications Standards Institute (ETSI)) and in the literature. The objective of this work is to present a formal specification that unifies these different views of service topologies. A taxonomy is proposed which allows the classification of topologies according to multiple criteria, including structure, size, heterogeneity, function sharing, among others. We also propose the CUstom Service TOpology Model (CUSTOM), a specification model that allows the design of network service topologies that feature the different categories proposed in the taxonomy. Finally, we demonstrate the specification capabilities of CUSTOM through a series of case studies.