**4. Interfaces design challenges and MOSA implementation**

This section addresses the design challenges and is divided into four subsections, including: (i) Subsection 4.1 discusses interface design and practical design issues; (ii) Subsection 4.2 introduces MOSA concept; (iii) Subsection 4.3 presents DOD MOSA guidance and the U.S. Naval Open Architecture (NOA); and (iv) Subsection 4.4 discusses MOSA tools and approach for MOSA implementation that addresses the design issues identified in Subsection 4.1.
