  Many real-world services can be provided through multiple virtual network
function (VNF) graphs, corresponding, e.g., to high- and low-complexity
variants of the service itself. Based on this observation, we extend the
concept of service scaling in network orchestration to service shifting, i.e.,
upgrading or downgrading the VNF graph to use among those implementing the same
service. Service shifting can serve multiple goals, from reducing operational
costs to reacting to infrastructure problems. Furthermore, it enhances the
flexibility of service-level agreements between network operators and third
party content providers ("verticals). In this paper, we introduce and describe
the service shifting concept, its benefits, and the associated challenges, with
special reference to how service shifting can be integrated within real-world
5G architectures and implementations. We conclude that existing network
orchestration frameworks can be easily extended to support service shifting,
and its adoption has the potential to make 5G network slices easier for the
operators to manage under high-load conditions, while still meeting the
verticals' requirements.
