  Network slicing enables multiple virtual networks to be instantiated and
customized to meet heterogeneous use case requirements over 5G and beyond
network deployments. However, most of the solutions available today face
scalability issues when considering many slices, due to centralized controllers
requiring a holistic view of the resource availability and consumption over
different networking domains. In order to tackle this challenge, we design a
hierarchical architecture to manage network slices resources in a federated
manner. Driven by the rapid evolution of deep reinforcement learning (DRL)
schemes and the Open RAN (O-RAN) paradigm, we propose a set of traffic-aware
local decision agents (DAs) dynamically placed in the radio access network
(RAN). These federated decision entities tailor their resource allocation
policy according to the long-term dynamics of the underlying traffic, defining
specialized clusters that enable faster training and communication overhead
reduction. Indeed, aided by a traffic-aware agent selection algorithm, our
proposed Federated DRL approach provides higher resource efficiency than
benchmark solutions by quickly reacting to end-user mobility patterns and
reducing costly interactions with centralized controllers.
