  Network slicing is considered a key mechanism to serve the multitude of
tenants (e.g. vertical industries) targeted by forthcoming 5G systems in a
flexible and cost-efficient manner. In this paper, we present a SDN/NFV
architecture with multi-tenancy support. This architecture enables a network
slice provider to deploy network slice instances for multiple tenants
on-the-fly, and simultaneously provision them with isolation guarantees.
Following the Network Slice as-a-Service delivery model, a tenant may access a
Service Catalog, selecting the slice that best fits its needs and ordering its
deployment. This work provides a detailed view on the stages that a network
slice provider must follow to deploy the ordered network slice instance,
accommodating it into a multi-domain infrastructure, and putting it operative
for tenant's consumption. These stages address critical issues identified in
the literature, including (i) the mapping from high-level service requirements
to network functions and infrastructure requirements, (ii) the admission
control, and (iii) the specific information a network slice descriptor should
have. With the proposed architecture and the recommended set of stages, network
slice providers can deploy (and later operate) slice instances with great
agility, flexibility, and full automation.
