In particular network ports or entire interfaces can be directly assigned to a

In particular network ports or entire interfaces can

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guest OS, enabling a flexible and lightweight deployment. In particular, network ports or entire interfaces can be directly assigned to a container without incurring an overhead as in the case of hypervisor-based solutions. On the other hand, sharing the kernel also raises concerns regarding security and (performance) isolation between instances. Finally, worth mentioning are also unikernel [ 22 ] as well as serverless [ 23 ], [ 24 ] technologies for the virtualization of network functions, that sits at the opposite side of the spectrum as the former targets full flexibility with light-weight monolithic kernels that run on a hypervisor such as Xen, whereas the latter targets performance by trading it for a more constrained environment offering a set of Application Program Interface (APIs). All these technologies are still competing, and there is no single candidate that fits all use-cases, which makes the ecosystem very rich. 2) Network Virtualization.: In a similar fashion to hardware virtualization, network virtualization (NV) accomplishes an abstraction of network resources and therefore acts as an enabler for fully programmable networks whose entire stack can be provisioned in a flexible manner. The survey in [ 25 ] provides an overview of NV approaches that are categorized w.r.t. several characteristics. These include the network tech- nology that is virtualized, the layer in the network stack at which virtualization is performed, as well as the granularity of virtualized entities. Depending on the envisioned use case, operators need to decide on an NV technology that satisfies the corresponding requirements. An additional step in the evolution of NV consists of combining the NV idea of sharing a physical substrate among several stakeholders with the SDN paradigm. By introducing an SDN hypervisor, it is possible to virtualize SDN-based networks and therefore allow multiple tenants to deploy their own SDN-based network including their own controllers while operating on one common physical infrastructure. A survey of SDN hypervisors is available in [ 26 ]. The main distinctions between different of these hypervisors include their architec- ture, the network attributes that are abstracted, as well as the capabilities in terms of isolation between slices. Our work leverages the technologies described in [ 26 ] and clearly build upon [ 25 ]: specifically, we go one step further with respect to [ 25 ] by understanding how functions can be implemented and, especially, accelerated with either software, hardware or hybrid approaches. C. Integration into the Orchestration Context Given the abstractions and flexibility of the outlined virtual- ization mechanisms, management and orchestration (MANO) techniques can attach to interfaces that are defined in frame- works such as ETSI MANO [ 27 ] and adapt the resource allocation of individual VNF types and instances in a dynamic fashion. Additionally, knowledge regarding a VNF’s resource requirements and performance levels given a specific resource enables scaling VNFs according to observed demands. An
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