  The upcoming Sixth Generation (6G) mobile communications system envisions
supporting a variety of use cases with differing characteristics, e.g., very
low to extremely high data rates, diverse latency needs, ultra massive
connectivity, sustainable communications, ultra-wide coverage etc. To
accommodate these diverse use cases, the 6G system architecture needs to be
scalable, modular, and flexible; both in its user plane and the control plane.
In this paper, we identify some limitations of the existing Fifth Generation
System (5GS) architecture, especially that of its control plane. Further, we
propose a novel architecture for the 6G System (6GS) employing Software Defined
Networking (SDN) technology to address these limitations of the control plane.
The control plane in existing 5GS supports two different categories of
functionalities handling end user signalling (e.g., user registration,
authentication) and control of user plane functions. We propose to move the
end-user signalling functionality out of the mobile network control plane and
treat it as user service, i.e., as payload or data. This proposal results in an
evolved service-driven architecture for mobile networks bringing increased
simplicity, modularity, scalability, flexibility and security to its control
plane. The proposed architecture can also support service specific signalling
support, if needed, making it better suited for diverse 6GS use cases. To
demonstrate the advantages of the proposed architecture, we also compare its
performance with the 5GS using a process algebra-based simulation tool.
