  Prior to the advent of the cloud, storage and processing services were
accommodated by specialized hardware, however, this approach introduced a
number of challenges in terms of scalability, energy efficiency, and cost. Then
came the concept of cloud computing, where to some extent, the issue of massive
storage and computation was dealt with by centralized data centers that are
accessed via the core network. The cloud has remained with us thus far,
however, this has introduced further challenges among which, latency and energy
efficiency are of the pinnacle. With the increase in embedded devices
intelligence came the concept of the Fog. The availability of massive numbers
of storage and computational devices at the edge of the network, where some are
owned and deployed by the end-users themselves but most by service operators.
This means that cloud services are pushed further out from the core towards the
edge of the network, hence reduced latency is achieved. Fog nodes are massively
distributed in the network, some benefit from wired connections, and others are
connected via wireless links. The question of where to allocate services
remains an important task and requires extensive attention. This chapter
introduces and evaluates cloud fog architectures in 6G networks paying special
attention to latency, energy efficiency, scalability, and the trade-offs
between distributed and centralized processing resources.
