  With the advent of revolutionary technologies, such as virtualization and
softwarization, a novel concept for 5G networks and beyond has been unveiled:
Network Slicing. Initially driven by the research community, standardization
bodies as 3GPP have embraced it as a promising solution to revolutionize the
traditional mobile telecommunication market by enabling new business models
opportunities. Network Slicing is envisioned to open up the telecom market to
new players such as Industry Verticals, e.g. automotive, smart factories,
e-health, etc. Given the large number of potential new business players, dubbed
as network tenants, novel solutions are required to accommodate their needs in
a cost-efficient and secure manner. In this paper, we propose NSBchain, a novel
network slicing brokering (NSB) solution, which leverages on the widely adopted
Blockchain technology to address the new business models needs beyond
traditional network sharing agreements. NSBchain defines a new entity, the
Intermediate Broker (IB), which enables Infrastructure Providers (InPs) to
allocate network resources to IBs through smart contracts and IBs to assign and
re-distribute their resources among tenants in a secure, automated and scalable
manner. We conducted an extensive performance evaluation by means of an
open-source blockchain platform that proves the feasibility of our proposed
framework considering a large number of tenants and two different consensus
algorithms.
