  The Open Radio Access Network (Open RAN)-which is being standardized, among
others, by the O-RAN Alliance-is bringing a radical transformation to the
cellular ecosystem through the notions of disaggregation and RAN Intelligent
Controllers (RICs). The latter enable closed-loop control through custom logic
applications, namely xApps and rApps, supporting control decisions at different
timescales. However, the current O-RAN specifications lack of a practical
approach to execute real-time control loops operating at timescales below 10ms.
In this paper, we propose the notion of dApps, distributed applications that
complement existing xApps/rApps by allowing operators to implement fine-grained
data-driven management and control in real-time at the Central Units
(CUs)/Distributed Units (DUs). dApps receive real-time data from the RAN, as
well as enrichment information from the near-real-time RIC, and execute
inference and control of lower-layer functionalities, thus enabling use cases
with stricter timing requirements than those considered by the RICs, such as
beam management and user scheduling. We propose feasible ways to integrate
dApps in the O-RAN architecture by leveraging and extending interfaces and
components already present therein. Finally, we discuss challenges specific to
dApps, and provide preliminary results that show the benefits of executing
network intelligence through dApps.
