The  System Design Document (SDD) describes the high-level system

 The  System Design Document (SDD) describes the high-level system design and the low-level detailed design specifications from which a system is built. As part of the security development team, this document provides the information necessary for designing and implementing a system.

Create a system design document making sure to:

Describe the design goals and considerations.
Provide a high-level overview of the system architecture.
Describe the data design associated with the system.
Describe the human-machine interface and operational scenarios.
Design a drawing appropriate for implementation. The high-level system design should be further decomposed into low-level detailed design specifications for each system component, including hardware, internal communications, software, system integrity controls, and external interfaces.
Refer to the "System Design Document," provided within the required readings as an example. Note: Only the criteria listed above is required within the System Design Document; additional sections are not required.