4G and 4 for 5G combine all functional components associated with a given partitioning/use-case into a single deeply embedded SoC, like shown below in Fig. 4- 13: The level of integration implemented here is both the advantage and the Achilles heel of this approach: either the solution matches the problem-statement very well, or not at all. This goes both for choice of Instruction Set Architecture for the L2 stack, the Physical layer implementation, protocol (4G? 5G?) and IO pieces of the puzzle. Deeply integrated solutions are often seen used in macro base station implementations from the established industry players. A challenge is how to deal with a "scale out" scenario where-for example-we need to support a larger amount of front- and mid/backhaul. Adding an external Ethernet switch to the system for a scale-out purpose defies the target of integration and adds cost to the system that cannot be carried. Orthogonal to the deeply integrated approach, a more disaggregated option is shown below in Fig. 4-14: This approach overcomes the challenge of scalability: each of the key components in the system can be scaled independently of the other ones and selected (from different vendors) 154 Open Radio Access Network (O-RAN) Systems Architecture and Design Integrated Baseband SoC Layer 2/Stack Backhaul IO Fronthaul IO Physical Layer Ethernet eCPRI Accel. 6 X 25G 2 x25G FIGURE 4-13 Deeply integrated/embedded approach. on their own merits. Typical implementations of the fronthaul functionality would be using an FPGA. The host processor can be x86 or Arm based and Physical Layer accelerations can be FPGA and/or ASSP/ASIC such as. 5 The software defined solution is a simplification from the disaggregated approach for those use-cases where the required system capacity allows us to combine multiple functions into a single device, for example, the front and mid/backhaul functionality that can be com- bined with the host processor (assuming the host processor has sufficient networking IO) and we only offload limited Physical