  We study the benefits of adopting server disaggregation in the fog computing
tier by evaluating energy efficient placement of interactive apps in a future
fog 6G network. Using a mixed integer linear programming (MILP) model, we
compare the adoption of traditional server (TS) and disaggregated server (DS)
architectures in a fog network comprising of selected fog computing sites in
the metro and access networks. Relative to the use of TSs, our results show
that the adoption of DS improves the energy efficiency of the fog network and
enables up to 18% reduction in total fog computing power consumption. More
instances of interactive fog apps are provisioned in a fog network that is
implemented over a network topology with high delay penalty. This ensures that
minimal delay is experienced by distributed users. Our result also shows that
the proximity of fog computing sites such as metro-central offices and radio
cell sites to geo-distributed users of interactive fog applications make them
important edge locations for provisioning moderately delay sensitive fog apps.
However, fog applications with more stringent delay thresholds require in situ
processing at directly connected radio cell sites or at the location of the
requesting users. Finally, we propose a heuristic for energy efficient and
delay aware placement of interactive fog apps in a fog network which replicates
the trends observed during comprehensive analysis of the exact results obtained
by solving the MILP model formulated in this paper. Our results and proposed
MILP and heuristic provide a good reference and tool for fog network design and
deployment.
