  Mobile Networks today comprise of multiple Radio Access Technologies (RATs),
e.g., 4G LTE, Wireless Local Area Network (WLAN), and the upcoming 5G-New Radio
(5G-NR). The access networks of these RATs are controlled by RAT-specific
entities, e.g., the resource management function located inside an individual
LTE eNB is used for the eNB control, or access controllers are used for
controlling WLAN Access Points. Even in the 3GPP's 5G architecture, which has a
common Core supporting multiple RATs, radio access related decisions are taken
independently within individual RATs. Due to the fragmented nature of
control-plane in multi-RAT Radio Access Network (RAN), a unified global view of
network resources is unavailable, hindering optimized allocation of resources.
It also brings complexity to the features involving multiple RATs, e.g., dual
connectivity. To address these issues, we introduced an SDN-based Multi-RAT RAN
architecture (SMRAN) in our earlier work [arXiv:1812.11825], where the RAN
control-plane is segregated from the data-plane. As part of the SMRAN
architecture, we defined a logically centralized multi-RAT RAN Controller and
individual RAT-specific data-plane functions. In the current work, we define a
protocol, called Open5G, to be used for control and management of the SMRAN
data-plane. Open5G is based on OpenFlow (OF) and OF-Config, which are commonly
used protocols in the SDN-based wired networks and data centers.
